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INFRAHYOID NECK
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HEAD AND NECK IMAGING
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INFRAHYOID NECK Robert Sigal, MD, PhD
one to obtain high quality three-dimensional reconstructions or coronal and sagittal reformations, provided that breathing and motion artifacts are limited.z9
Imaging plays an important role in the management of neck disease. It allows one to identify true disease versus pseudomasses, to show the exact location and extent of a lesion, and to predict the nature of the lesion. This article concentrates on neck disease excluding the lymph nodes, larynx and hypopharynx, and thyroid.
MR Imaging
MR imaging has become a prominent imaging method in the cervical region. The well-known advantages (superior tissue contrast and multiplanar capabilities) are to be balanced with potential technical limitations. The first limitation is the need to use a dedicated head and neck coil, which allows one to visualize the entire head and neck region. This type of antenna (generally a double Helmholtz coil) is not commonly found in all MR imaging units (cervical surface coils used for cervical spine imaging do not offer sufficient coverage because of limited superior-inferior field of view and limited depth of penetration). The other limitations are due to motion artifacts: swallowing, respiratory, and blood motion artifacts are especially troublesome in the neck region. The ability to overcome these inconveniences by using appropriate counter measures (flow compensation, inplane and out of plane saturation, gating) is the hallmark of high-quality MR imaging units and experienced radiographers and radiologists. Water bags placed on each side of the patient’s neck can be used to load the surface coil better, reducing the so-called bulk magnetic susceptibility artifact. A study typically includes a sagittal T1-weighted; axial (or axial oblique parallel to the plane of the vocal cords) T1-weighted; and T2-weighted spin echo (SE) sequences. T2-weighted images can be acquired with either conventional SE technique (which provides proton density images in the same set of images) or fast spin echo (FSE) with or
TECHNIQUES
Standard Radiographs
Barium swallow can be used to confirm a Zenker ‘s diverticulum, and fistulograms can identify the course of a branchia1 apparatus fistula or postsurgical fistula. CT
CT is the method of reference. As a rule, the study should completely cover the entire head and neck region because disease located in the neck can extend or disseminate from the suprahyoid region or be caused by a process in this region. Therefore, the scanning area should extend from the skull base (external auditory canal) to the thoracic inlet (superior aspect of the manubrium). Avoiding dental amalgam by using proper angulation of the gantry is mandatory. Contiguous 3- to 5-mm slices are obtained in the axial plane. Contrast enhancement must be performed in such a way that constant opacification of the arteries and veins is obtained and that contrast uptake in a lesion can be seen. Double windowing (soft tissues and bone or cartilage algorithm) is necessary when a lesion affects the laryngeal cartilages or the spinal column. The use of spiral techniques allows _
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From the Head and Neck Section, Department of Imaging, Institut Gustave Roussy, Paris XI University, Villejuif, France
RADIOLOGIC CLINICS OF NORTH AMERICA VOLUME 36 NUMBER 5 SEETEMBER 1998
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without fat suppression, if available. FSE is preferable to conventional SE because the shorter acquisition time minimizes the risk of motion artifacts. Gadolinium injection is needed when a tumor or an infection is suspected. After injection, images are acquired in the axial plane with an orthogonal acquisition performed either in the sagittal or coronal plane. Fat saturation techniques are critical in the neck where fat is always present because they allow better delineation of the limits of contrast take-up. The choice of the field of view (FOV), matrix size, slice thickness, and number of excitations is a compromise between the signal-to-noise ratio and spatial resolution. On a 1.5-T unit, for a T1-weighted sequence, the authors routinely use a 16-cm FOV, 4-mm thickness, 192 X 256 matrix, and one excitation. The FSE T2-weighted sequence is acquired with a 18- to 20-cm FOV. MR angiography has been used to demonstrate flow within lesions and represents a familiar imaging display for surgical planning7 Imaging of Brachial Plexopathy. CT evaluation should cover the area extending from the hyoid bone to the thoracic arch. Contrast injection is routinely performed. Undermagnification at the neck level and overmagnification when the thoracic inlet is reached should be avoided by properly adjusting the magnification factor. CT has two drawbacks: (1) beam-hardening artifacts from the shoulders may preclude good visualization of the thoracic inlet and (2) direct image acquisition is limited to the axial plane. In the latest CT units, specific software packages allow reduction of beam-hardening artifacts. CT myelography is the reference method for intradural evaluation of the brachial plexus roots. MR imaging is considered the modality of choice because of its direct multiplanar imaging capabilities and its ability to differentiate the brachial plexus from the surrounding vascular structure~.~, 17, 24, 26, 27, 29 The body coil leads to poor signal-to-noise images. The use of a shoulder coil, cervical spinal coil, or dedicated head and neck coil is preferable. Respiratory motion compensation is recommended to reduce breathing a r t i f a ~ t s .One ~ ~ should obtain at least two imaging planes. The anatomy of the brachial plexus is best displayed on T1-weighted sequences. T2-weighted images identify abnormal tissues. Gadolinium injection, with and without fat-suppressed T1-weighted sequences, is valuable for the depiction of neoplastic disease.” Sonography
Sonography is performed with a high-frequency probe (7.5 to 13 MHz). Color Doppler and power Doppler sonography help to identify vascular structures. This technique is not used by all radiologic teams. Its main advantages are its low cost and easy accessibility, which allows guidance for fine needle aspiration. The main drawbacks are that it does not explore the deep structures, is
operator dependent, and does not provide the clinician with reference images.
Angiography
This technique is not used anymore for diagnostic procedures. Interventional angiography is used in the preoperative work-up of paragangliomas to reduce the bleeding risks.
NORMAL ANATOMY
The traditional presentation, which is still pertinent to physical examination of the neck, is based on the concept of neck triangles. The sternocleidomastoid muscle divides the neck into the anterior and posterior triangles. The anterior triangle is subdivided into carotid, muscular, submental, and submandibular triangles. The posterior triangle is subdivided into occipital and subclavian triangles (Fig. 1). Modern cross-sectional imaging has profoundly modified the perception of the anatomy of the neck because it permits direct identification of the main deep structures. The three layers of deep cervical fascia (not directly visualized) enclose and separate different compartments or anatomic spaces (Fig. 2). We present the nomenclature popularized by Harnsberger,’2 which has become commonly utilized among head and neck radiologists (although other descriptions exisP). The principal infrahyoid spaces are the visceral, carotid, posterior cervical, retropharyngeal, and perivertebral spaces (Table 1).Besides the visceral space, which is unique to the infrahyoid neck, all the other spaces extend from the skull base to the thoracic inlet or below, and have been compared with vertical elevator shafts that represent natural conduits for tumor or infectious spread.I2The retropharyngeal space continues inferiorly to the level of the T4 vertebral body. This substantiates the need to explore radiologically both the supra and infrahyoid neck, and when needed the superior mediastinum. In normal patients the infrahyoid retropharyngeal space is hardly visible as a thin flattened fatty band (seen at the suprahyoid level, lymph nodes can be seen, especially in children and young adults). The superficial (investing) layer of the deep cervical fascia, which completely surrounds the neck, splits to encircle the sternocleidomastoid and trapezius muscles, which therefore do not belong to the previously mentioned spaces. An additional minor space is referred to as the anterior cervical space, which is a purely fatty space lying lateral to the visceral space, anterior to the carotid space, and medial to the sternocleidomastoid muscle.
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Figure 1. Head and neck triangles. A, Anterior view and 13,lateral view. The suprahyoid neck is subdivided into the submandibular (A) and submental (B) triangles. The infrahyoid neck consists of the carotid (C), muscular (D), occipital (E), and subclavian (F) triangles. 1 = Anterior belly of digastric muscle; 2 = stylohyoid muscle; 3 = posterior belly of digastric muscle; 4 = superior belly of omohyoid muscle; 5 = sternocleidomastoid muscle; 6 = trapezius muscle; 7 = inferior belly of omohyoid muscle.
DISEASES Congenital
Branchial Apparatus Embryologic anomalies of the branchial (pharyngeal) arches manifest as cysts, fistulae, and sinuses, either external or internal. Knowledge of the embryologic basis of these defects helps one to understand these anomalies?, 37 Vestigial remnants result from incomplete obliteration of the branchial apparatus or buried cell rests, which can form cysts later in life. First branchial cleft cystsz," are located at the suprahyoid level in the parotid region and are typically connected to the external auditory canal. Second branchial anomalies account for more than 95% of all branchial disorders." l9 Anomalies can occur anywhere between the tonsillar fossa and the anterior border of the junction of the middle and lower third of the sternocleidomastoidmuscle. Cysts, which are far more common than sinuses and fistulae, typically lie at the angle of the mandible and are noticed after a trauma or a viral upper respiratory tract infection. Radiologically, a typical cyst appears as a thin-rimmed, smoothly marginated mass located anterior to the sternocleidomastoid muscle, displacing the carotid medially and the submandibular gland anteriorly.21Theoretically, medial extension of the cyst between the external and internal artery is pathognomonic, but is seldom observed. The cyst usually presents with low CT attenuation and low T1-weighted and high
T2-weighted signal intensity (Fig. 3). Diving ranula may present with similar characteristics, but the correct diagnosis is made when a tail or dilatation of the submandibular duct (Wharton's duct) is identified in the sublingual space (Fig. 4).6The appearance may become more solid when there is
Figure 2. Deep spaces at the level of the infrahyoid neck (contrast injected CT scan). The white line represents the different layers of the deep cervical fascia. 1 = Visceral space; 2 = carotid space; 3 = posterior cervical space; 4* = periveriebral space, anterior portion; 4*' = perivertebral space, posterior portion; 5 = retropharyngeal space; 6 = anterior cervical space; 7 = sternocleidomastoid muscle; 8 = trapezius muscle.
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Table 1. SPACE AND CONTENTS OF THE INFRAHYOID NECK ~~
Corresponding Neck Triangle
Contents
Differential Diagnosis
None
Fat (lymph nodes at the suprahyoid level)
Skull base to mediastinum
None
Prevertebral portion Prevertebral and scalene muscles Brachial plexus roots Phrenic nerve Vertebral artery and nerve Vertebral body and pedicle Paraspinal portion Paraspinal muscles Posterior elements
Visceral Space
Hyoid bone to mediastinum
Muscular
Thyroid gland Parathyroid glands Larynx Trachea Hypopharynx Esophagus Recurrent laryngeal nerves Lymph nodes (paratracheal)
Carotid Space
Skull base (jugular foramen) to aortic arch
Carotid
Common carotid artery Internal jugular vein Vagus nerve (cranial nerve X) Sympathetic chain Deep cervical lymph nodes
Posterior Cervical Space
Skull base to clavicles
Occipital and subclavian
Fat Spinal accessory nerve (cranial nerve XI) Spinal accessory lymph nodes Preaxillary brachial plexus
Pseudomass Tortuous carotid artery Congenital Lymphangioma, hemangioma Infectious Adenopathy, cellulitis, abscess Benign neoplasms Lipoma Malignancies Direct invasion from primary pharyngeal squamous cell carcinoma Pseudomass Vertebral body osteophyte, cervical rib, levator scapulae hypertrophy, anterior disk herniation Infectious Vertebral spondylodiskitis Benign neoplasms Neural sheath tumor (brachial plexus), chordoma, and other vertebral body benign tumor Malignancies Vertebral body and epidural metastasis, nonHodgkin’s lymphoma, vertebral body malignant tumor, sarcoma (including brachial plexus neurosarcoma) Pseudomass Thyroid pyramidal lobe or prominent isthmus Congenital Thyroid gland: thyroglossal duct cysts Infectious Thyroid gland: thyroiditis Benign neoplasms Thyroid gland: goiter, colloid cyst, adenoma Parathyroid glands: adenoma, cyst Larynx: laryngocele Esophagus: Zenker’s diverticulum Malignancies Thyroid: carcinoma (papillary, follicular, anaplastic), non-Hodgkin’s lymphoma, metastasis Larynx and hypopharynx: squamous cell carcinoma Esophagus: carcinoma Lymph nodes: metastases from thyroid and subglottic laryngeal carcinoma, lymphoma Pseudomass Carotid bulb and internal jugular vein asymmetry, carotid artery ectasia Congenital Second branchial cleft cyst Infectious Deep cervical chain adenopathy, abscess Benign neoplasms Carotid body tumor, neural sheath tumor Malignancies Deep cervical chain adenopathy Vascular Internal jugular vein thrombosis, asymmetric internal jugular vein; carotid artery dissection and pseudoaneurysm Congenital Lymphangioma, hemangioma, third branchial cleft cysts Infectious Abscess, spinal accessory cervical chain adenopathy Benign neoplasms Lipoma, neural sheath tumor Malignancies Spinal accessory cervical chain adenopathy, liposarcoma
Space
Extent
Retropharyngeal Space
Skull base to mediastinum (T3)
Perivertebral Space
Adapted from Harnsberger HR: Handbook of Head and Neck Imaging, ed 2, Vol 1. St. Louis, Mosby, 1995; with permission.
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normal embryologic descent of the thymic primordium into the mediastinum. Thymic cysts, aberrant cervical thymus, and persistent thymopharyngeal ducts are predominantly found in the left side of the neck from the mandible to the mediastin11m.3~ Thyroglossal Duct Cyst
Figure 3. Second branchial cyst. Contrast-enhanced axial CT scan. The lesion (arrow) is lateral to the internal
carotid artery and jugular vein, posterior to the submandibular gland (curved arrow), and is medial to the sternocleidomastoid muscle (open arrow). It is a noncomplicated cyst with no identifiable wall and a low attenuation watery content.
increased proteinaceous content (Fig. 5 ) . In fact, the real radiologic challenge comes from actively infected cysts that present with thick, irregular enhancing margins making them indistinguishable from necrotic lymph nodes with extracapsular tumor spread. In a practical situation the lesion is surgically removed to ensure diagnosis; in addition, surgery is the sole treatment for a branchial cyst and the best therapeutic option for an isolated metastatic lymph node. Third branchial cleft cysts are rare. They are located in the posterior cervical space. Thymic anomalies are also congenital anomalies of the branchial apparatus% and result from ab-
The thyroglossal duct occurs along the residual tract left by the thyroid gland after its descent from the foramen cecum at the tongue base to its final position in the visceral space. In 5% of cases thyroid elements remain" and may give rise to thyroglossal duct cysts; fistulae; or solid nodules of thyroid tissue (the latter mostly found in the region of the foramen cecum (lingual thyroid). The thyroglossal duct cyst is the most common midline neck mass. Fifty percent of the lesions are diagnosed during infancy. The cyst is located at the level of the hyoid bone (150/, to 50% of cases) or below it (25% to 65% of cases). The suprahyoid location is observed in 20% to 25% of cases.25The typical cyst is deep to or embedded in the infrahyoid strap muscles. The more inferior the cyst, the more likely it is to be off the midline." At imaging, the CT density and MR imaging signal depend on the uncomplicated or infected characteristics of the lesion (Fig. 6). Lyrnphangioma and Hernangiorna
Lymphangiomas are congenital malformations of lymphatic channels. Seventy-five percent of the lesions are detected before the age of 3 years.I3 The three types of lymphangioma are (1) cystic hygroma; (2) cavernous lymphangiomas; and (3) capillary lymphangiomas, with the size of the lymphatic spaces decreasing from the former to the latter.Is The lesion is preferably found in the posterior cervical space, but frequently presents as a
Figure 4. Diving ranula. Contrast-enhanced axial CT scans. A, At the level of the hyoid bone, the lesion herniates from the sublingual space, mimicking a second branchial cyst. B, The section obtained at the level of the oral cavity shows dilatation of the submandibular duct (arrow).
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Figure 5. Second branchial cyst. A, Axial T1-weighted view. The lesion (arrow) has no identifiable wall. Its content shows a signal intensity close to that of muscle, indicating high proteinaceous content. B, On the coronal T2-weighted scan, high signal intensity suggests the cystic nature of this mass.
transspatial mass, found in multiple contiguous spaces." CT scans show a low-density, nonenhancing, multilocular mass. MR imaging scans demonstrate either low signal intensity on T1-weighted images or high signal intensity due to hyperproteinaceous contents, fat, or methemoglobin.28The lesion exhibits high signal intensity on T2weighted images (Fig. 7). Cyst walls and septae may enhance after contrast injection. MR imaging is essential to demonstrate the exact extent of this lesion, which tends to surround critical neurovascular structures.11The spinal accessory nerve in particular is almost always involved, but the brachial plexus, carotid arteries, and vagus nerve may also be in jeopardy.l3 Hemangiomas are vascular rests subdivided in
Figure 6. Thyroglossal duct cyst. Contrast-enhanced axial CT scan. The lesion is entrapped within the strap muscles. Absence of peripheral contrast enhancement indicates a noncomplicatedcyst.
three types: (1) capillary, (2) cavernous, and (3) mixed types. On CT and MR imaging studies, hemangiomas intensively enhance after contrast media injection. The presence of phleboliths on CT is highly suggestive of the diagnosis. Lymphangioma and hemangioma may inflammatory Abscess and Cellulitis
Spread of a suppurative process may come from an infected site in the aerodigestive tract, such as
Figure 7. Cystic lymphangioma. Axial T2-weighted MR scan discloses a lobulated high signal intensity mass that infiltrates the posterior cervical space and extends anteriorly and medially to the carotid space. The internal carotid artery is slightly displaced medially, but still patent (arrow).
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Figure 8. Neck abscess. Contrast-enhanced axial CT scan. The abscess extends into the sternocleidomastoid muscle (arrowheads) and abuts the common carotid artery (straight arrow). Abnormal enhancement reaches the wall of the right pyriform sinus (curved arrow). Poor margination, central low attenuation fluid collection, and diffuse contrast enhancement could mimick a jugulodigastric necrotic lymph node with extracapsular spread.
tonsillitis, pharyngitis, or an odontogenic infection. Neck abscesses can also be due to extracapsular spread of infected lymph nodes in the carotid or posterior cervical spaces. Intravenous drug use by way of the internal jugular vein is another etiologic factor.13In 50% of patients an etiologic site of origin is not identified.16 Radiologically, infection typically presents as an ill-defined, poorly marginated, heterogeneous, contrast-enhanced lesion. Transspatial extension (i.e., involving more than one space) is frequently encountered. Imaging helps to differentiate abscesses that present with at least one fluid cavity (Fig. 8) and cellulitis visualized as areas of contrast enhancement. Administration of high-dose antibi-
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otics is necessary in both cases, but abscesses frequently require transcervical incision and drainage. Necrotizing cervical fascia1 infection is an extremely virulent type of infection due to mixed aerobic and anaerobic infection in an immunocompromised Gas from gas-forming organisms is directly identified at CT. Lymph nodes in the retropharyngeal spaces may be seeded with bacteria from infected sites in the nose, sinonasal cavities, and pharynx. Although these lymph nodes lie at the suprahyoid level, abscesses resulting from extracapsular spread can disseminate in the entire retropharyngeal space. Retropharyngeal infection tends to be more frequent in children.16 Infection and abscess may also result from direct trauma (foreign body) or iatrogenic causes (endoscopy, intubation, nasogastric tube placement) (Figs. 9 and 10). Because the physical examination may be unremarkable, imaging is essential to make the diagnosis. The typical abscess appears as an area with low CT attenuation and high T2-weighted signal intensity. Peripheral contrast enhancement is characteristically present. The hallmark of a retropharyngeal abscess is the vertical extension from the skull base to T4. Vertebral Body Spondylodiskitis
Vertebral body osteomyelitis may extend anteriorly into the perivertebral and retropharyngeal spaces. They can be indistinguishable radiologically from vertebral neoplasms (usually metastases) (Fig. 11). Tumor Benign
Carotid Body Tumor. In the neck, paragangliomas are found at the level of the carotid bifurcation, hence their name. The role of imaging is not
Figure 9. Retropharyngeal abscess following traumatic intubation. Contrast-enhanced axial CT scans. A, The abscess lies in the retropharyngeal space (arrows) with limited extension to the visceral space (curved arrow). €3, The inferior extent of the lesion (arrow) is seen at the level of the aortic arch.
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Figure 10. Retrophatyngeal abscess. A, On the sagittal T2-weighted view, the fluid collection has a typical high signal intensity appearance (arrow). B, The axial gadolinium (Gd)-enhanced fat-suppressed T1-weighted view shows the active enhancing portion of the abscess. The relationships with the other spaces are evidenced: The lesion abuts both carotid spaces, but the carotid arteries still demonstrate the typical flow void pattern (arrowheads), indicating patency. The right internal jugular vein is enlarged and thrombosed (open arrow). The abscess extends into the right portion of the visceral space (curved arrow), close to the cricoid cartilage. The longus colli muscles (long straight arrows) are normal, indicating that the perivertebral space is spared. (Courtesy of D. Doyon, MD, Le Kremlin-Bicbtre, France.)
only to confirm the presence of a carotid body tumor, but also to rule out multiple lesions, which are found in 3% to 5% of patients overall and 20% to 30% with a family history.lzAt CT, carotid body tumors strongly enhance with contrast (Fig. 12),
Figure 11. Cervical spondylodiskitis. Ti-weighted MR view (right) and Gd-T1-weighted MR view (leff). Contrastenhanced areas indicate infection. They are seen in the perivertebral space, extending from C l to T1-T2 (arrowheads), in the vertebral bodies and disk (curved arrow), and in the epidural space of the spinal canal. (arrows) (Courtesy of D. Doyon, MD, Le Kremlin-Bicbtre, France.)
making them indistinguishable from vascular schwannomas. MR imaging is the imaging modality of choice. On coronal or sagittal views, glomus tumors present as long-axis ovoid masses with a higher signal intensity than that of muscles on all sequences.Z3,31 Serpiginous low intensity areas representing flow voids coexist with high signal intensity foci representing subacute hemorrhage (free methemoglobin). This leads to a
Figure 12. Carotid body tumor. On the contrast-enhanced axial CT scan, the lesion has a well-defined, smoothly marginated, strongly enhancing mass located between the external (straight arrow) and internal (open arrow) carotid arteries (arrowhead indicates internal jugular vein).
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characteristic ”salt and pepper” a p p e a r a n ~ e . ~ ~ Neural Sheath Tumor. Schwannoma and neurofibroma arising in the neck are located in the caWhen these findings are not found, which is frequent in lesions less than 2 cm in size, the diagnorotid space (vagus nerve or sympathetic chain) or in the posterior cervical space (spinal nerve or sis may be difficult to establish. Location between brachial p l e ~ u s ) . ’The ~ vagus nerve is the most the external and internal carotid arteries suggests commonly involved cranial nerve in the neck.13In the correct diagnosis (Fig. 13). MR angiography patients with von Recklinghausen’s disease, multitime of flight does not show intralesional flow. It shows the splaying of the external and internal ple lesions of the peripheral nerves and central carotid arteries, a finding already demonstrated nervous system are common findings. In these patients MR imaging examination should be exon MR imaging.7Angiography is only needed for tended to the entire neuraxis. preoperative embolization.
Figure 13. Bilateral carotid body tumor. On the contrast-enhanced axial CT scan (A) the lesions (arrows) are strongly enhancing. On the sagittal T1-weighted view (B) and axial TBweighted view (C), it is less the salt and pepper appearance than the location between the external and internal branches of the carotid arteries (identified in C because of their flow void) (arrows), which helps to make the diagnosis. Conventionalangiography (D), performed for preoperative embolization, confirms the diagnosis but does not provide additional diagnostic information.
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Figure 14. Vagus nerve cystic schwannoma. Clinical examination was unremarkable.Contrast-enhancedaxial CT scan. The appearance of this lesion, with central low attenuation and peripheral contrast enhancement, is not specific. The only clue to the correct diagnosis is the location between the carotid bifurcation (arrows) and internal jugular vein (curved arrow).
Several criteria can help to suggest the diagnosis of neurogenic tumors: Presence of a well-circumscribed long-axis fusiform-shaped mass. Location posterior to the internal and common carotid arteries and internal jugular vein for vagus nerve and sympathetic nervous system schwannomas. On CT the tumors are usually isodense to muscles. Low-density lesions correspond either to
neurofibromas or to cystic schwannomas (Fig. 14). Fatty degeneration has been observed in large neurofibromas. On MR imaging nerve sheath tumors display an intermediate signal intensity on T1weighted images and a high signal intensity on T2-weighted images, with possible low signal intensity foci (Fig. 15)?l,33 After gadolinium injection, contrast uptake is variable. It may be very intense in vascular schwannomas.
Figure 15. Vagus nerve schwannoma. The patient has von Reckinghausen’s disease. A, The left parasagittal fast SE TP-weighted view shows a heterogeneous well-circumscribed lesion (arrow) with peripheral high signal intensity and central low signal intensity.The lesion abuts the pulmonary apex (arrowhead). 8,The axial view displays the inferior portion of the tumor in the superior mediastinum and its relationships with the arteries. The left carotid artery (open arrow) abuts the mass and the left subclavian artery (arrow) appears embedded within the lesion. Flow void indicates that both vessels are patent.
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In such cases, dynamic MR imaging has been proposed to differentiate paragangliomas with an early vascular dip and peak from vascular nerve sheath tumors with a slightly delayed peakJ6 Lipoma. Lipomas are encapsulated collections of mature fat cells that are predominantly found in the posterior cervical space (Fig. 16), but may occur in other spaces including the retropharyngeal space (Figs. 17 and 18). They are easily identified by their low density on CT or high signal intensity on T1-weighted MR images. If a nonfatty area is displayed in the lipoma, two diagnoses should be considered: (1) a rare liposarcoma or (2) h e m ~ r r h a g eLipomas .~~ tends to enlarge with weight gain, but do not decrease with weight 10~s.37
Neoplastic
Sarcoma. Sarcomas primarily arise in the posterior cervical space. Liposarcomas are identified thanks to their fatty content. Rhabdomyosarcoma, neurofibrosarcoma,and fibrosarcoma have no distinct radiologic findings. Ill-defined margins and
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extension to the vertebral bodies and neural axis suggest an aggressive lesion (Fig. 19), but these lesions may present with well-defined borders (Fig. 20). Histologically benign lesions, such as aggressive fibromatosis, can share the same characteristics (Fig. 21)? The lack of specificity underscores the need for biopsy. Direct Invasion from Primary Tumor. Squamous cell carcinoma may extend outside the visceral space. Laryngeal and pyriform sinus tumors can grow laterally into the carotid space. Tumors of the posterior hypopharyngeal wall can invade the retropharyngeal space. Extension to the perivertebral space is uncommon. Chordoma, Vertebral Body Metastasis. These lesions may extend anteriorly in the perivertebral and retropharyngeal spaces. Radiologically, the tumor is centered on one or several vertebral bodies. Vascular Aneurysms of the cervical carotid and vertebral arteries are usually associated with atherosclerotic disease. Traumatic pseudoaneurysms are secondary to a disruption in arterial wall continuity with subsequent encapsulation of the periarterial hematoma. The diagnosis can be established with ultrasound, CT, or MR imaging including MR angiography. MR imaging examination of the brain is needed to evaluate the consequences of the arterial lesion. Thromboses of the internal jugular vein are associated with drug abuse, central venous catheterization, or head and neck cancer. During the acute phase the vein is enlarged and heterogeneous both on CT and MR imaging (see Fig. 10). In malignancy, the diagnosis can be hazardous if only one level is examined because acute venous thrombosis and metastatic lymph nodes with central necrosis and extracapsular spread may share the same characteristics and coexist (Fig. 22). In fact, recognition of the tubular nature of the vascular lesion makes the diagnosis easy. Pseudomass Tortuous Common or Internal Carotid Artery
Figure 16. Posterior neck lipoma. Contrast-enhanced axial CT scan. A, At the laryngeal level, the lipoma (arrow) occupies the posterior cervical space. There is a mass effect on the carotid space, and the internal jugular vein is hardly visible (arrowhead). B, The mass (arrow) extends into the thoracic inlet.
A tortuous common or internal carotid artery can manifest as a pulsatile mass in the carotid triangle at physical examination. It can also present as a submucosal mass displacing the pharyngeal posterior wall. At the level of the infrahyoid neck, palpation is not feasible and the pulsatile characteristic of the mass is overlooked. On contrast-enhanced CT scan, the diagnosis is straightforward, provided that iodine concentration is sufficient within the lumen (Fig. 23). At MR imaging the vessel typically shows the flow void pattern. MR angiography can help to convince the clinician, but is not indispensible.
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Figure 17. Retropharyngeal lipoma. Axial CT scans. The low attenuation well-marginated fatty mass extends along the retropharyngeal space from the oropharynx (A), through the neck (B)down to the mediastinum (C).
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Figure 18. Retropharyngeal lipoma. On the sagittal T1weighted view, the tumor (arrow) is disclosed as a high signal intensity mass extending in front of C2 and C6. Because both longus colli muscles are slightly off-midline, the retrophatyngeal mass is directly in contact with the anterior aspect of the vertebral bodies.
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Figure 19. Synovial sarcoma. Contrast-enhanced axial CT scan. Location in the posterior neck musculature of the perivertebral space indicates a mesenchymal origin.
Figure 20. Neck relapse from a parotid sarcoma. A, The axial Gd-enhanced fat suppressed T1weighted view shows a strongly enhancing mass that extends into the perivertebral space and carotid space and completely surrounds the left internal carotid artery (straight arrow). The involvement of the hypoglossal nerve (XII) in the carotid space is evidenced by abnormal signal intensity in ipsilateral tongue musculature (curved arrow). Encasement of the vertebral artery (arrowhead) is also displayed. Notice previous parotidectomy deformity (open arrow) with no abnormal contrast take up. B, The coronal view displays the superior-inferior extent of the tumor and shows invasion of the vertebral body of C2 (arrow).
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Figure 21. Aggressive fibromatosis. Contrast-enhanced axial CT scan. The mass shows intense and homogeneous enhancement. It seems well-circumscribed, but these lesions are known to be infiltrative and adherent, especially to vascular and neural structures.
Asymmetric Internal Jugular Vein The internal jugular vein is extremely variable at presentation. Internal jugular veins can be markedly asymmetric. A large, tubular, enhancing mass located lateral to the carotid should n o t be mistaken for a vascular tumor.
Vertebral Body Osteophyte, Cervical Rib, and Large or Asymmetric Transverse Process Vertebral b o d y osteophytes m a y manifest as a submucosal mass displacing the posterior pharyn-
Figure 22. Internal jugular vein associated with a metastatic lymph node. Contrast-enhancedaxial CT scan. The patient presented with a squamous cell carcinoma of the left pyriform sinus (not seen at this level). The thrombosed vein (straight arrow) and the jugulodigastric lymph node with extracapsular spread (curved arrow) share similar imaging features.
Figure 23. Tortuous common carotid artery. Contrastenhanced axial CT scan. The patient presented with a laryngeal squamous cell carcinoma (not seen at this level). At endoscopy, the physician reported bulging of the posterior pharyngeal wall. Imaging discloses a retropharyngeal enhancing vessel (straight arrow). It also shows a jugulodigastric metastatic lymph node (curved arrow).
geal wall. Cervical ribs and large or asymmetric transverse processes m a y present clinically as posterior cervical masses. Diagnosis is easy at CT or p l a i n films (Fig. 24).
Levator Scapulae Hypertrophy Levator scapulae hypertrophy is a consequence of radical neck dissection during w h i c h the sternocleidomastoid muscle is removed and the spinal accessory nerve is sacrificed leading to trapezius muscle atrophy. As a compensation, the levator scapulae muscle hypertrophies and can be per-
Figure 24. Vertebral body osteophyte. This mass presented at endoscopy as a submucosal mass displacing the posterior pharyngeal wall. Axial CT scan (bone algorithm) shows an osteophyte lying in the anterior portion of the perivertebral space.
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ceived clinically as a mass. The diagnosis at imaging is not always easy because the symmetric anatomic landmarks are lost. Absence of contrast enhancement and knowledge of the clinical history are the keys to diagnosis. SternocleidomastoidFibroma of Neonates
This is probably the most common lateral neck mass in neonates. It is also known as congenital torticollis and fibrornatosis ~ 0 l l i . IIt~ corresponds to a swelling or lump within the sternocleidomastoid muscle, often related to birth trauma. The diagnosis is based on physical examination. Brachial Plexopathies
Brachial plexopathies can be categorized as traumatic or nontraumatic, each of them accounting for approximately 50% of ~ases.2~ Traumatic Injuries
Accurate assessment of the site and extent of the injury is mandatory in injuries of the brachial plexus. Trauma may be due to traction, compression, penetrating injuries, local fractures, or disloc a t i o n ~ .Clinical ~~ and electrophysiologic studies are not very reliable.4 The determination of the exact location of the injury, extradural or intradural, directly affects the patient's prognosis and surgical strategy? CT myelography provides a reliable diagnosis of the extent of intradural damage? The accuracy of CT myelography is 85% using intraoperative findings as the gold standard? MR imaging is less effective to demonstrate intradural root avulsion (52% in Carvalho's et a14 series) because patients are not able to lie as still as required resulting in motion artifacts. Technical improvements, with shorter scan times, increased spatial resolution, and reduced cerebrospinal fluid artifacts, should overcome this inconvenience. MR imaging offers good depiction of the brachial plexus beyond the spinal foramen. When avulsion of a nerve root results in a pseudomeningocele it is visualized on axial or coronal T2-weighted images as a high signal intensity extra-arachnoid collection of cerebrospinal fluid around the missing nerve root. In the case of acute or subacute injury, a hematoma may be visible (Fig. 25). In infants with birth-related brachial plexus injury, CT myelography requires general anesthesia and can be replaced by MR imaging.* FSE TZ-weighted imaging can be used as a triage examination: the existence of a pseudomeningocele indicates the need for operation; in case of normal MR imaging findings, conservative management with close follow-up can be undertaken" Nontraumatic Lesions
Nontraumatic lesions include neoplasms, radiation fibrosis, brachial neuritis, nodal metastases,
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and symptomatic cervical ribs. Among primary neoplasms, schwannomas and neurofibromas are the most common lesions. These tumors tend to be well circumscribed with a markedly high signal intensity on T2-weighted images and strong conneurofibrosartrast e n h a n ~ e m e n t .z7~Although ~, comas tend to present with infiltrating margins (Fig. 26), no reliable criteria allow differentiation of benign from malignant peripheral nerve tumors with ~ e r t a i n t y The . ~ ~ brachial plexus may be directly invaded by primary tumors of the lung (Pancoast's tumor); bone; soft tissues in the neck; supraclavicular fossa; and upper part of the thorax. Coronal and sagittal MR imaging are particularly helpful to predict the resectability of the lesion. Lymph node metastases and intraspinal metastases may involve nerve roots. Radiation fibrosis may occur 5 to 20 years after therapy. It is unlikely with doses less than 60 Gy. There are no definite imaging criteria to differentiate recurrent or metastatic disease from postirradiation injury. CT-guided biopsy is recommended. Flaps and Posttherapeutic Changes
Cancer treatment usually requires surgical treatment, neck irradiation, or a combination of both techniques. Imaging plays an important role in the follow-up of these patients, who are often difficult to examine clinically.l,lo, 30, 3* After neck dissection and reconstructive surgery with myocutaneous flaps, CT or MR imaging can suggest the presence of tumor relapse or abscess (Fig. 27). After radiotherapy, contrast enhancement frequently corresponds to acute or subacute inflammatory changes and can be difficult to differentiate from tumor relapse (Fig. 28). Biopsy or sequential imaging follow-up permits one to establish the diagnosis. Comparison with baseline studies (usually CT) is recommended.Zo,30 IMAGING STRATEGIES
Clinical examination and endoscopy are essential in the selection of imaging techniques and strategy. Often, the patient presents with a neck mass with or without additional symptoms (pharyngeal discomfort, hoarseness). A malignant lesion (most often a squamous cell carcinoma) of the larynx, nasopharynx, oropharynx, hypopharynx, and oral cavity may be diagnosed by the physician and confirmed by pathology. The radiologist helps to define the exact extent of the primary lesion and should perform a complete lymph node survey. CT or MR imaging are the techniques of choice. If clinical examination of the superior aerodigestive tract is nonspecific, imaging is essential to establish the positive diagnosis by showing a true mass (versus a pseudomass). In addition, by demonstrating the exact space of origin of the lesion and its characteristics (CT density, MR imaging
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Figure 25. Brachial plexus trauma (one week). A, An axial view shows a pseudomeningocele, displayed as a collection of cerebrospinal fluid lateral to the thecal sac (white arrow). Increased signal intensity muscle corresponding to hematoma and edema is displayed outside the neural foramen (open arrow) and in the region of the anterior left scalene (curved arrow). 6, On the coronal view, the entire length of the left anterior scalene muscle has increased signal intensity (arrows). (Courtesy of C. Beigelman, MD, S. Lenoir, MD, HBpital Pitie-Salpetriere, France.)
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Figure 26. Brachial plexus neurofibrosarcoma. A, Contrast-enhanced axial CT scan. The illdefined, heterogeneous lesion invades the right perivertebral space and extends into the neural foramen (arrow). B, On the coronal Gd-T1-weighted view, the tumor seems embedded within the scalene muscles (open arrows), above the subclavian artery (straight arrow).
Figure 27. Post-therapeuticabscess. Total laryngectomy with myocutaneousflap transplant was performed for pyriform sinus squamous cell carcinoma. A, Contrast-enhanced axial CT scan shows an abscess (arrow) that extends into the fatty portion of the graft and opens into the skin. B, On fistulogram, the abscessed cavity (curved arrow) communicates with the base of the tongue (straight arrow) via an abnormally strictured pharyngeal canal (arrowhead).
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Figure 28. Postradiotherapy inflammation. The patient presented with an advanced hypopharyngeal tumor and was treated with external radiotherapy. An enhancing lesion is disclosed in the left perivertebral space (arrow). Biopsy did not disclose tumor recurrence.
signal, homogeneity or heterogeneity, contour, contrast enhancement), imaging can suggest the correct diagnosis. It can guide a biopsy or conversely prevent a procedure that may be dangerous (e.g., a hypervascular mass). Ultrasound can be used to confirm a clinical impression of a superficial, benign lesion (such as a lipoma). Cross-sectional imaging, however, is recommended if there is a suspicion that the lesion is deeply seated or invasive. In the case of a submucosal mass (i.e., deforming the pharyngeal-laryngeal wall), imaging can show the origin of the lesion and predict or affirm its nature (vertebral osteophyte, tortuous carotid artery). Specific clinical context can also orient the diagnosis. Fever and pain points to infection, nerve palsy to neural sheath tumor, and a bruit to chemodectoma. For infectious disease evaluation, CT is preferable because it allows one to recognize air, a salivary gland calculus, or a dental abscess. If there is a high suspicion of neoplasm, MR imaging is the preferred modality because it offers multiplanar, multiparameter information and identifies multicentricity or bilaterality (often associated with a familial syndrome). Specific clinical presentations focus the diagnosis on the thyroid or parathyroid glands. If a brachial plexopathy is suspected, MR imaging should be performed. The diagnosis of root avulsion can necessitate the use of myelo CT. ACKNOWLEDGMENTS The author would like to thank Amaud Chkron for the preparation of the photographs and Nicolas Denoisc for the preparation of the drawing (Fig. 1).
References 1. Becker M, Schroth G, Zbaren P, et al: Long-term changes induced by high-dose irradiation of the head
and neck region: Imaging findings. Radiographics 175-26, 1997 2. Benson MT, Dalen K, Mancuso AA, et al: Congenital anomalies of the branchial apparatus: Embryology and pathologic anatomy. Radiographics 12943-960, 1992 3. Bilbey JH, Lamond RG, Mattrey FS: MR imaging of disorders of the brachial plexus. J Magn Reson Imaging 4:13-18, 1994 4. Carvalho GA, Nikkhah G, Matthies C, et a1 Diagnosis of root avulsions in traumatic brachial plexus injuries: Value of computerized tomography myelography and magnetic resonance imaging. J Neurosurg 8669-76, 1997 5. Cobby MJD, Leslie IJ, Watt I: Cervical myelography of nerve root avulsion injuries using water-soluble contrast media. Br J Radio1 61:673-678, 1988 6. Coit WE, Hamsberger HR, Osbom AG, et a1 Ranulas and their mimics: CT evaluation. Radiology 163211216,1987 7. Colletti PM, Terk MR, Zee C S Magnetic resonance angiography in neck masses. Computerized Medical Imaging and Graphics 20379-388, 1996 8. Francel PC, Koby M, Park TS, et al: Fast spin-echo magnetic resonance imaging for radiological assessment of neonatal brachial plexus injury. J Neurosurg 83461466, 1995 9. Garant M, Remy H, Just N: Aggressive fibromatosis of the neck: MR findings. AJNR Am J Neuroradiol 183429-1431, 1997 10. Gussack G, Hudgins P: Imaging modalities in recurrent head and neck tumors. Laryngoscope 101:119124, 1991 11. Hamsberger H R Cystic masses of the head and neck. In Handbook of Head and Neck Imaging, ed 2. St Louis, Mosby, 1995, pp 199-223 12. Harnsberger H R Handbook of Head and Neck Imaging, ed 2, vol 1. St. Louis, Mosby, 1995 13. Hawkins D B Cysts, primary tumors, and infections of the neck. In Meyerhoff WL, Rice DH (eds): Otolaryngology-Head and Neck Surgery. Philadelphia, WB Saunders, 1992, pp 713-728 14. Hilal S, Ascheri G, Chynn G, Baredea S Carotid space and related cervical spaces: Neurogenic tumors. Radiology 150:729-735, 1984 15. Hudgins PA, Burson JG, Gussack GS, et a1 CT and MR appearance of recurrent malignant head and neck neoplasms after resection and flap reconstruction. AJNR Am J Neuroradiol 15:1689-1694, 1994 16. Johnson ]T: Abscesses and deep space infections of the head and neck. Infect Dis Clin North Am 6:705717, 1992 17. Kneeland JB, Kellman GM, Middleton WD, et al: Diagnosis of diseases of the supraclavicular region by use of MR imaging. AJR Am J Roentgenol 148:1149-1151, 1987 18. Landing BH, Farber S: Tumors of the cardiovascular system. In Atlas of Tumor Pathology, vol7. Washington, DC, Armed Forces Institute of Pathology, 1956 19. Liston SL, Siege1 LG: Branchial cysts, sinuses, and fistulas. Ear Nose Throat J 58:9-17, 1979 20. Mancuso A: Imaging in patients with head and neck cancer. In Million RR, Cassisi NJ (eds): Management of Head and Neck Cancer. A Multidisciplinary Approach. Philadelphia, JB Lippincott, 1994, pp 43-59 21. Miller MB, Rao VM, Barry MT Cystic masses of the head and neck Pitfalls in CT and MR interpretation. AJR Am J Roentgenol 159:601-607,1992 22. Mukherji SK, Tart R, et al: Evaluation of first
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23. 24. 25. 26. 27. 28. 29. 30. 31.
branchial anomalies by CT and MR. Comput Assist Tomogr 17576-581,1993 Olsen WL, Dillon WP, Kelly WM, et al: MR imaging of paragangliomas. AJNR Am J Neuroradiol 10391042, 1986 Posniak HV, Olson MC, Dudiak CM, et al: MR imaging of the brachial plexus. AJR Am J Roentgenol 161:373-379, 1993 Pound LA: Neck masses of congenital origin. Pediatr Clin North Am 288414344,1981 Rapoport S, Blair DN, McCarthy SM, et al: Brachial plexus: Correlation of MR imaging with CT and pathologic findings. Radiology 167161-165, 1988 Reede DL: Brachial plexus. In Som PM, Curtin HD (eds): Head and Neck Imaging, vol 2. Baltimore, Mosby, 1996, pp 976-991 Sieeel MI, Glazer HS. St Amour TE. et al: Lvmuhanv giomas in children: MR imaging. Radiology 170:467470, 1989 Smoker WRK: Normal anatomy of the neck. In Som I'M, Curtin HD (eds): Head and Neck Imaging, vol 2. Baltimore, Mosby, 1996, pp 711-737 Som PM: Postoperative neck. In Som PM, Curtin HD (eds): Head and Neck Imaging, vol 2. Baltimore, Mosby, 1996, pp 992-1005 Som PM, Braun IF, Shapiro MD, et al: Tumors of the parapharyngeal space and upper neck MR imaging characteristics. Radiology 164823-829, 1987 . I ,
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32. Sorn PM, Curtin HD: Fasciae and spaces. In Som PM, Curtin HD (eds): Head and Neck Imaging, vol 2. Baltimore, Mosby, 1996, pp 738-746 33. Suh IS, Abenoza P, Galloway HR, et al: Peripheral (extracranial) nerve tumors: Correlation of MR imaging and histologic findings. Radiology 183:341346, 1992 34. Tori F, Mares AJ: The aberrant cervical thymus: Embryology, pathology, and clinical implication. Am J Surg 136:631437,1978 35. Tovi F, Fliss DM, Zirkin HJ: Necrotizing soft-tissue infections in the head and neck: A clinicopathological study. Laryngoscope 101:619-625, 1991 36. Vogl TJ, Mack MG, Juergens M, et al: Skull base tumors: Gadodiamide injection-enhanced MR imaging drop-out effect in the early enhancement pattern of paragangliomas versus different tumors. Radiology 188339, 1993 37. Weisman JL: Nonnodal masses of the neck. In Som I'M, Curtin HD (eds): Head and Neck Imaging, vol 2. Baltimore, Mosby, 1996, pp 794-822 38. Wester DJ, Singer S, et al: Imaging of the postoperative neck with emphasis on surgical flaps and their complications. AJR Am J Roentgenol 164:989-993, 1995 39. Zadvinskis DI', Benson MT, Kerr HH, et al: Congenital malformations of the cervicothoracic lymphatic system: Embryology and pathogenesis. Radiographics 121175-1189, 1992
Address reprint requests to Robert Sigal, MD, PhD Department of Imaging Institut Gustave Roussy 94805 Villejuif Cedex France e-mail: [email protected]
HEAD AND NECK IMAGING
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INFRAHYOID NECK Robert Sigal, MD, PhD
one to obtain high quality three-dimensional reconstructions or coronal and sagittal reformations, provided that breathing and motion artifacts are limited.z9
Imaging plays an important role in the management of neck disease. It allows one to identify true disease versus pseudomasses, to show the exact location and extent of a lesion, and to predict the nature of the lesion. This article concentrates on neck disease excluding the lymph nodes, larynx and hypopharynx, and thyroid.
MR Imaging
MR imaging has become a prominent imaging method in the cervical region. The well-known advantages (superior tissue contrast and multiplanar capabilities) are to be balanced with potential technical limitations. The first limitation is the need to use a dedicated head and neck coil, which allows one to visualize the entire head and neck region. This type of antenna (generally a double Helmholtz coil) is not commonly found in all MR imaging units (cervical surface coils used for cervical spine imaging do not offer sufficient coverage because of limited superior-inferior field of view and limited depth of penetration). The other limitations are due to motion artifacts: swallowing, respiratory, and blood motion artifacts are especially troublesome in the neck region. The ability to overcome these inconveniences by using appropriate counter measures (flow compensation, inplane and out of plane saturation, gating) is the hallmark of high-quality MR imaging units and experienced radiographers and radiologists. Water bags placed on each side of the patient’s neck can be used to load the surface coil better, reducing the so-called bulk magnetic susceptibility artifact. A study typically includes a sagittal T1-weighted; axial (or axial oblique parallel to the plane of the vocal cords) T1-weighted; and T2-weighted spin echo (SE) sequences. T2-weighted images can be acquired with either conventional SE technique (which provides proton density images in the same set of images) or fast spin echo (FSE) with or
TECHNIQUES
Standard Radiographs
Barium swallow can be used to confirm a Zenker ‘s diverticulum, and fistulograms can identify the course of a branchia1 apparatus fistula or postsurgical fistula. CT
CT is the method of reference. As a rule, the study should completely cover the entire head and neck region because disease located in the neck can extend or disseminate from the suprahyoid region or be caused by a process in this region. Therefore, the scanning area should extend from the skull base (external auditory canal) to the thoracic inlet (superior aspect of the manubrium). Avoiding dental amalgam by using proper angulation of the gantry is mandatory. Contiguous 3- to 5-mm slices are obtained in the axial plane. Contrast enhancement must be performed in such a way that constant opacification of the arteries and veins is obtained and that contrast uptake in a lesion can be seen. Double windowing (soft tissues and bone or cartilage algorithm) is necessary when a lesion affects the laryngeal cartilages or the spinal column. The use of spiral techniques allows _
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From the Head and Neck Section, Department of Imaging, Institut Gustave Roussy, Paris XI University, Villejuif, France
RADIOLOGIC CLINICS OF NORTH AMERICA VOLUME 36 NUMBER 5 SEETEMBER 1998
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without fat suppression, if available. FSE is preferable to conventional SE because the shorter acquisition time minimizes the risk of motion artifacts. Gadolinium injection is needed when a tumor or an infection is suspected. After injection, images are acquired in the axial plane with an orthogonal acquisition performed either in the sagittal or coronal plane. Fat saturation techniques are critical in the neck where fat is always present because they allow better delineation of the limits of contrast take-up. The choice of the field of view (FOV), matrix size, slice thickness, and number of excitations is a compromise between the signal-to-noise ratio and spatial resolution. On a 1.5-T unit, for a T1-weighted sequence, the authors routinely use a 16-cm FOV, 4-mm thickness, 192 X 256 matrix, and one excitation. The FSE T2-weighted sequence is acquired with a 18- to 20-cm FOV. MR angiography has been used to demonstrate flow within lesions and represents a familiar imaging display for surgical planning7 Imaging of Brachial Plexopathy. CT evaluation should cover the area extending from the hyoid bone to the thoracic arch. Contrast injection is routinely performed. Undermagnification at the neck level and overmagnification when the thoracic inlet is reached should be avoided by properly adjusting the magnification factor. CT has two drawbacks: (1) beam-hardening artifacts from the shoulders may preclude good visualization of the thoracic inlet and (2) direct image acquisition is limited to the axial plane. In the latest CT units, specific software packages allow reduction of beam-hardening artifacts. CT myelography is the reference method for intradural evaluation of the brachial plexus roots. MR imaging is considered the modality of choice because of its direct multiplanar imaging capabilities and its ability to differentiate the brachial plexus from the surrounding vascular structure~.~, 17, 24, 26, 27, 29 The body coil leads to poor signal-to-noise images. The use of a shoulder coil, cervical spinal coil, or dedicated head and neck coil is preferable. Respiratory motion compensation is recommended to reduce breathing a r t i f a ~ t s .One ~ ~ should obtain at least two imaging planes. The anatomy of the brachial plexus is best displayed on T1-weighted sequences. T2-weighted images identify abnormal tissues. Gadolinium injection, with and without fat-suppressed T1-weighted sequences, is valuable for the depiction of neoplastic disease.” Sonography
Sonography is performed with a high-frequency probe (7.5 to 13 MHz). Color Doppler and power Doppler sonography help to identify vascular structures. This technique is not used by all radiologic teams. Its main advantages are its low cost and easy accessibility, which allows guidance for fine needle aspiration. The main drawbacks are that it does not explore the deep structures, is
operator dependent, and does not provide the clinician with reference images.
Angiography
This technique is not used anymore for diagnostic procedures. Interventional angiography is used in the preoperative work-up of paragangliomas to reduce the bleeding risks.
NORMAL ANATOMY
The traditional presentation, which is still pertinent to physical examination of the neck, is based on the concept of neck triangles. The sternocleidomastoid muscle divides the neck into the anterior and posterior triangles. The anterior triangle is subdivided into carotid, muscular, submental, and submandibular triangles. The posterior triangle is subdivided into occipital and subclavian triangles (Fig. 1). Modern cross-sectional imaging has profoundly modified the perception of the anatomy of the neck because it permits direct identification of the main deep structures. The three layers of deep cervical fascia (not directly visualized) enclose and separate different compartments or anatomic spaces (Fig. 2). We present the nomenclature popularized by Harnsberger,’2 which has become commonly utilized among head and neck radiologists (although other descriptions exisP). The principal infrahyoid spaces are the visceral, carotid, posterior cervical, retropharyngeal, and perivertebral spaces (Table 1).Besides the visceral space, which is unique to the infrahyoid neck, all the other spaces extend from the skull base to the thoracic inlet or below, and have been compared with vertical elevator shafts that represent natural conduits for tumor or infectious spread.I2The retropharyngeal space continues inferiorly to the level of the T4 vertebral body. This substantiates the need to explore radiologically both the supra and infrahyoid neck, and when needed the superior mediastinum. In normal patients the infrahyoid retropharyngeal space is hardly visible as a thin flattened fatty band (seen at the suprahyoid level, lymph nodes can be seen, especially in children and young adults). The superficial (investing) layer of the deep cervical fascia, which completely surrounds the neck, splits to encircle the sternocleidomastoid and trapezius muscles, which therefore do not belong to the previously mentioned spaces. An additional minor space is referred to as the anterior cervical space, which is a purely fatty space lying lateral to the visceral space, anterior to the carotid space, and medial to the sternocleidomastoid muscle.
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-4 L
A
B
5
. .
Figure 1. Head and neck triangles. A, Anterior view and 13,lateral view. The suprahyoid neck is subdivided into the submandibular (A) and submental (B) triangles. The infrahyoid neck consists of the carotid (C), muscular (D), occipital (E), and subclavian (F) triangles. 1 = Anterior belly of digastric muscle; 2 = stylohyoid muscle; 3 = posterior belly of digastric muscle; 4 = superior belly of omohyoid muscle; 5 = sternocleidomastoid muscle; 6 = trapezius muscle; 7 = inferior belly of omohyoid muscle.
DISEASES Congenital
Branchial Apparatus Embryologic anomalies of the branchial (pharyngeal) arches manifest as cysts, fistulae, and sinuses, either external or internal. Knowledge of the embryologic basis of these defects helps one to understand these anomalies?, 37 Vestigial remnants result from incomplete obliteration of the branchial apparatus or buried cell rests, which can form cysts later in life. First branchial cleft cystsz," are located at the suprahyoid level in the parotid region and are typically connected to the external auditory canal. Second branchial anomalies account for more than 95% of all branchial disorders." l9 Anomalies can occur anywhere between the tonsillar fossa and the anterior border of the junction of the middle and lower third of the sternocleidomastoidmuscle. Cysts, which are far more common than sinuses and fistulae, typically lie at the angle of the mandible and are noticed after a trauma or a viral upper respiratory tract infection. Radiologically, a typical cyst appears as a thin-rimmed, smoothly marginated mass located anterior to the sternocleidomastoid muscle, displacing the carotid medially and the submandibular gland anteriorly.21Theoretically, medial extension of the cyst between the external and internal artery is pathognomonic, but is seldom observed. The cyst usually presents with low CT attenuation and low T1-weighted and high
T2-weighted signal intensity (Fig. 3). Diving ranula may present with similar characteristics, but the correct diagnosis is made when a tail or dilatation of the submandibular duct (Wharton's duct) is identified in the sublingual space (Fig. 4).6The appearance may become more solid when there is
Figure 2. Deep spaces at the level of the infrahyoid neck (contrast injected CT scan). The white line represents the different layers of the deep cervical fascia. 1 = Visceral space; 2 = carotid space; 3 = posterior cervical space; 4* = periveriebral space, anterior portion; 4*' = perivertebral space, posterior portion; 5 = retropharyngeal space; 6 = anterior cervical space; 7 = sternocleidomastoid muscle; 8 = trapezius muscle.
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Table 1. SPACE AND CONTENTS OF THE INFRAHYOID NECK ~~
Corresponding Neck Triangle
Contents
Differential Diagnosis
None
Fat (lymph nodes at the suprahyoid level)
Skull base to mediastinum
None
Prevertebral portion Prevertebral and scalene muscles Brachial plexus roots Phrenic nerve Vertebral artery and nerve Vertebral body and pedicle Paraspinal portion Paraspinal muscles Posterior elements
Visceral Space
Hyoid bone to mediastinum
Muscular
Thyroid gland Parathyroid glands Larynx Trachea Hypopharynx Esophagus Recurrent laryngeal nerves Lymph nodes (paratracheal)
Carotid Space
Skull base (jugular foramen) to aortic arch
Carotid
Common carotid artery Internal jugular vein Vagus nerve (cranial nerve X) Sympathetic chain Deep cervical lymph nodes
Posterior Cervical Space
Skull base to clavicles
Occipital and subclavian
Fat Spinal accessory nerve (cranial nerve XI) Spinal accessory lymph nodes Preaxillary brachial plexus
Pseudomass Tortuous carotid artery Congenital Lymphangioma, hemangioma Infectious Adenopathy, cellulitis, abscess Benign neoplasms Lipoma Malignancies Direct invasion from primary pharyngeal squamous cell carcinoma Pseudomass Vertebral body osteophyte, cervical rib, levator scapulae hypertrophy, anterior disk herniation Infectious Vertebral spondylodiskitis Benign neoplasms Neural sheath tumor (brachial plexus), chordoma, and other vertebral body benign tumor Malignancies Vertebral body and epidural metastasis, nonHodgkin’s lymphoma, vertebral body malignant tumor, sarcoma (including brachial plexus neurosarcoma) Pseudomass Thyroid pyramidal lobe or prominent isthmus Congenital Thyroid gland: thyroglossal duct cysts Infectious Thyroid gland: thyroiditis Benign neoplasms Thyroid gland: goiter, colloid cyst, adenoma Parathyroid glands: adenoma, cyst Larynx: laryngocele Esophagus: Zenker’s diverticulum Malignancies Thyroid: carcinoma (papillary, follicular, anaplastic), non-Hodgkin’s lymphoma, metastasis Larynx and hypopharynx: squamous cell carcinoma Esophagus: carcinoma Lymph nodes: metastases from thyroid and subglottic laryngeal carcinoma, lymphoma Pseudomass Carotid bulb and internal jugular vein asymmetry, carotid artery ectasia Congenital Second branchial cleft cyst Infectious Deep cervical chain adenopathy, abscess Benign neoplasms Carotid body tumor, neural sheath tumor Malignancies Deep cervical chain adenopathy Vascular Internal jugular vein thrombosis, asymmetric internal jugular vein; carotid artery dissection and pseudoaneurysm Congenital Lymphangioma, hemangioma, third branchial cleft cysts Infectious Abscess, spinal accessory cervical chain adenopathy Benign neoplasms Lipoma, neural sheath tumor Malignancies Spinal accessory cervical chain adenopathy, liposarcoma
Space
Extent
Retropharyngeal Space
Skull base to mediastinum (T3)
Perivertebral Space
Adapted from Harnsberger HR: Handbook of Head and Neck Imaging, ed 2, Vol 1. St. Louis, Mosby, 1995; with permission.
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normal embryologic descent of the thymic primordium into the mediastinum. Thymic cysts, aberrant cervical thymus, and persistent thymopharyngeal ducts are predominantly found in the left side of the neck from the mandible to the mediastin11m.3~ Thyroglossal Duct Cyst
Figure 3. Second branchial cyst. Contrast-enhanced axial CT scan. The lesion (arrow) is lateral to the internal
carotid artery and jugular vein, posterior to the submandibular gland (curved arrow), and is medial to the sternocleidomastoid muscle (open arrow). It is a noncomplicated cyst with no identifiable wall and a low attenuation watery content.
increased proteinaceous content (Fig. 5 ) . In fact, the real radiologic challenge comes from actively infected cysts that present with thick, irregular enhancing margins making them indistinguishable from necrotic lymph nodes with extracapsular tumor spread. In a practical situation the lesion is surgically removed to ensure diagnosis; in addition, surgery is the sole treatment for a branchial cyst and the best therapeutic option for an isolated metastatic lymph node. Third branchial cleft cysts are rare. They are located in the posterior cervical space. Thymic anomalies are also congenital anomalies of the branchial apparatus% and result from ab-
The thyroglossal duct occurs along the residual tract left by the thyroid gland after its descent from the foramen cecum at the tongue base to its final position in the visceral space. In 5% of cases thyroid elements remain" and may give rise to thyroglossal duct cysts; fistulae; or solid nodules of thyroid tissue (the latter mostly found in the region of the foramen cecum (lingual thyroid). The thyroglossal duct cyst is the most common midline neck mass. Fifty percent of the lesions are diagnosed during infancy. The cyst is located at the level of the hyoid bone (150/, to 50% of cases) or below it (25% to 65% of cases). The suprahyoid location is observed in 20% to 25% of cases.25The typical cyst is deep to or embedded in the infrahyoid strap muscles. The more inferior the cyst, the more likely it is to be off the midline." At imaging, the CT density and MR imaging signal depend on the uncomplicated or infected characteristics of the lesion (Fig. 6). Lyrnphangioma and Hernangiorna
Lymphangiomas are congenital malformations of lymphatic channels. Seventy-five percent of the lesions are detected before the age of 3 years.I3 The three types of lymphangioma are (1) cystic hygroma; (2) cavernous lymphangiomas; and (3) capillary lymphangiomas, with the size of the lymphatic spaces decreasing from the former to the latter.Is The lesion is preferably found in the posterior cervical space, but frequently presents as a
Figure 4. Diving ranula. Contrast-enhanced axial CT scans. A, At the level of the hyoid bone, the lesion herniates from the sublingual space, mimicking a second branchial cyst. B, The section obtained at the level of the oral cavity shows dilatation of the submandibular duct (arrow).
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Figure 5. Second branchial cyst. A, Axial T1-weighted view. The lesion (arrow) has no identifiable wall. Its content shows a signal intensity close to that of muscle, indicating high proteinaceous content. B, On the coronal T2-weighted scan, high signal intensity suggests the cystic nature of this mass.
transspatial mass, found in multiple contiguous spaces." CT scans show a low-density, nonenhancing, multilocular mass. MR imaging scans demonstrate either low signal intensity on T1-weighted images or high signal intensity due to hyperproteinaceous contents, fat, or methemoglobin.28The lesion exhibits high signal intensity on T2weighted images (Fig. 7). Cyst walls and septae may enhance after contrast injection. MR imaging is essential to demonstrate the exact extent of this lesion, which tends to surround critical neurovascular structures.11The spinal accessory nerve in particular is almost always involved, but the brachial plexus, carotid arteries, and vagus nerve may also be in jeopardy.l3 Hemangiomas are vascular rests subdivided in
Figure 6. Thyroglossal duct cyst. Contrast-enhanced axial CT scan. The lesion is entrapped within the strap muscles. Absence of peripheral contrast enhancement indicates a noncomplicatedcyst.
three types: (1) capillary, (2) cavernous, and (3) mixed types. On CT and MR imaging studies, hemangiomas intensively enhance after contrast media injection. The presence of phleboliths on CT is highly suggestive of the diagnosis. Lymphangioma and hemangioma may inflammatory Abscess and Cellulitis
Spread of a suppurative process may come from an infected site in the aerodigestive tract, such as
Figure 7. Cystic lymphangioma. Axial T2-weighted MR scan discloses a lobulated high signal intensity mass that infiltrates the posterior cervical space and extends anteriorly and medially to the carotid space. The internal carotid artery is slightly displaced medially, but still patent (arrow).
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Figure 8. Neck abscess. Contrast-enhanced axial CT scan. The abscess extends into the sternocleidomastoid muscle (arrowheads) and abuts the common carotid artery (straight arrow). Abnormal enhancement reaches the wall of the right pyriform sinus (curved arrow). Poor margination, central low attenuation fluid collection, and diffuse contrast enhancement could mimick a jugulodigastric necrotic lymph node with extracapsular spread.
tonsillitis, pharyngitis, or an odontogenic infection. Neck abscesses can also be due to extracapsular spread of infected lymph nodes in the carotid or posterior cervical spaces. Intravenous drug use by way of the internal jugular vein is another etiologic factor.13In 50% of patients an etiologic site of origin is not identified.16 Radiologically, infection typically presents as an ill-defined, poorly marginated, heterogeneous, contrast-enhanced lesion. Transspatial extension (i.e., involving more than one space) is frequently encountered. Imaging helps to differentiate abscesses that present with at least one fluid cavity (Fig. 8) and cellulitis visualized as areas of contrast enhancement. Administration of high-dose antibi-
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otics is necessary in both cases, but abscesses frequently require transcervical incision and drainage. Necrotizing cervical fascia1 infection is an extremely virulent type of infection due to mixed aerobic and anaerobic infection in an immunocompromised Gas from gas-forming organisms is directly identified at CT. Lymph nodes in the retropharyngeal spaces may be seeded with bacteria from infected sites in the nose, sinonasal cavities, and pharynx. Although these lymph nodes lie at the suprahyoid level, abscesses resulting from extracapsular spread can disseminate in the entire retropharyngeal space. Retropharyngeal infection tends to be more frequent in children.16 Infection and abscess may also result from direct trauma (foreign body) or iatrogenic causes (endoscopy, intubation, nasogastric tube placement) (Figs. 9 and 10). Because the physical examination may be unremarkable, imaging is essential to make the diagnosis. The typical abscess appears as an area with low CT attenuation and high T2-weighted signal intensity. Peripheral contrast enhancement is characteristically present. The hallmark of a retropharyngeal abscess is the vertical extension from the skull base to T4. Vertebral Body Spondylodiskitis
Vertebral body osteomyelitis may extend anteriorly into the perivertebral and retropharyngeal spaces. They can be indistinguishable radiologically from vertebral neoplasms (usually metastases) (Fig. 11). Tumor Benign
Carotid Body Tumor. In the neck, paragangliomas are found at the level of the carotid bifurcation, hence their name. The role of imaging is not
Figure 9. Retropharyngeal abscess following traumatic intubation. Contrast-enhanced axial CT scans. A, The abscess lies in the retropharyngeal space (arrows) with limited extension to the visceral space (curved arrow). €3, The inferior extent of the lesion (arrow) is seen at the level of the aortic arch.
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Figure 10. Retrophatyngeal abscess. A, On the sagittal T2-weighted view, the fluid collection has a typical high signal intensity appearance (arrow). B, The axial gadolinium (Gd)-enhanced fat-suppressed T1-weighted view shows the active enhancing portion of the abscess. The relationships with the other spaces are evidenced: The lesion abuts both carotid spaces, but the carotid arteries still demonstrate the typical flow void pattern (arrowheads), indicating patency. The right internal jugular vein is enlarged and thrombosed (open arrow). The abscess extends into the right portion of the visceral space (curved arrow), close to the cricoid cartilage. The longus colli muscles (long straight arrows) are normal, indicating that the perivertebral space is spared. (Courtesy of D. Doyon, MD, Le Kremlin-Bicbtre, France.)
only to confirm the presence of a carotid body tumor, but also to rule out multiple lesions, which are found in 3% to 5% of patients overall and 20% to 30% with a family history.lzAt CT, carotid body tumors strongly enhance with contrast (Fig. 12),
Figure 11. Cervical spondylodiskitis. Ti-weighted MR view (right) and Gd-T1-weighted MR view (leff). Contrastenhanced areas indicate infection. They are seen in the perivertebral space, extending from C l to T1-T2 (arrowheads), in the vertebral bodies and disk (curved arrow), and in the epidural space of the spinal canal. (arrows) (Courtesy of D. Doyon, MD, Le Kremlin-Bicbtre, France.)
making them indistinguishable from vascular schwannomas. MR imaging is the imaging modality of choice. On coronal or sagittal views, glomus tumors present as long-axis ovoid masses with a higher signal intensity than that of muscles on all sequences.Z3,31 Serpiginous low intensity areas representing flow voids coexist with high signal intensity foci representing subacute hemorrhage (free methemoglobin). This leads to a
Figure 12. Carotid body tumor. On the contrast-enhanced axial CT scan, the lesion has a well-defined, smoothly marginated, strongly enhancing mass located between the external (straight arrow) and internal (open arrow) carotid arteries (arrowhead indicates internal jugular vein).
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characteristic ”salt and pepper” a p p e a r a n ~ e . ~ ~ Neural Sheath Tumor. Schwannoma and neurofibroma arising in the neck are located in the caWhen these findings are not found, which is frequent in lesions less than 2 cm in size, the diagnorotid space (vagus nerve or sympathetic chain) or in the posterior cervical space (spinal nerve or sis may be difficult to establish. Location between brachial p l e ~ u s ) . ’The ~ vagus nerve is the most the external and internal carotid arteries suggests commonly involved cranial nerve in the neck.13In the correct diagnosis (Fig. 13). MR angiography patients with von Recklinghausen’s disease, multitime of flight does not show intralesional flow. It shows the splaying of the external and internal ple lesions of the peripheral nerves and central carotid arteries, a finding already demonstrated nervous system are common findings. In these patients MR imaging examination should be exon MR imaging.7Angiography is only needed for tended to the entire neuraxis. preoperative embolization.
Figure 13. Bilateral carotid body tumor. On the contrast-enhanced axial CT scan (A) the lesions (arrows) are strongly enhancing. On the sagittal T1-weighted view (B) and axial TBweighted view (C), it is less the salt and pepper appearance than the location between the external and internal branches of the carotid arteries (identified in C because of their flow void) (arrows), which helps to make the diagnosis. Conventionalangiography (D), performed for preoperative embolization, confirms the diagnosis but does not provide additional diagnostic information.
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Figure 14. Vagus nerve cystic schwannoma. Clinical examination was unremarkable.Contrast-enhancedaxial CT scan. The appearance of this lesion, with central low attenuation and peripheral contrast enhancement, is not specific. The only clue to the correct diagnosis is the location between the carotid bifurcation (arrows) and internal jugular vein (curved arrow).
Several criteria can help to suggest the diagnosis of neurogenic tumors: Presence of a well-circumscribed long-axis fusiform-shaped mass. Location posterior to the internal and common carotid arteries and internal jugular vein for vagus nerve and sympathetic nervous system schwannomas. On CT the tumors are usually isodense to muscles. Low-density lesions correspond either to
neurofibromas or to cystic schwannomas (Fig. 14). Fatty degeneration has been observed in large neurofibromas. On MR imaging nerve sheath tumors display an intermediate signal intensity on T1weighted images and a high signal intensity on T2-weighted images, with possible low signal intensity foci (Fig. 15)?l,33 After gadolinium injection, contrast uptake is variable. It may be very intense in vascular schwannomas.
Figure 15. Vagus nerve schwannoma. The patient has von Reckinghausen’s disease. A, The left parasagittal fast SE TP-weighted view shows a heterogeneous well-circumscribed lesion (arrow) with peripheral high signal intensity and central low signal intensity.The lesion abuts the pulmonary apex (arrowhead). 8,The axial view displays the inferior portion of the tumor in the superior mediastinum and its relationships with the arteries. The left carotid artery (open arrow) abuts the mass and the left subclavian artery (arrow) appears embedded within the lesion. Flow void indicates that both vessels are patent.
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In such cases, dynamic MR imaging has been proposed to differentiate paragangliomas with an early vascular dip and peak from vascular nerve sheath tumors with a slightly delayed peakJ6 Lipoma. Lipomas are encapsulated collections of mature fat cells that are predominantly found in the posterior cervical space (Fig. 16), but may occur in other spaces including the retropharyngeal space (Figs. 17 and 18). They are easily identified by their low density on CT or high signal intensity on T1-weighted MR images. If a nonfatty area is displayed in the lipoma, two diagnoses should be considered: (1) a rare liposarcoma or (2) h e m ~ r r h a g eLipomas .~~ tends to enlarge with weight gain, but do not decrease with weight 10~s.37
Neoplastic
Sarcoma. Sarcomas primarily arise in the posterior cervical space. Liposarcomas are identified thanks to their fatty content. Rhabdomyosarcoma, neurofibrosarcoma,and fibrosarcoma have no distinct radiologic findings. Ill-defined margins and
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extension to the vertebral bodies and neural axis suggest an aggressive lesion (Fig. 19), but these lesions may present with well-defined borders (Fig. 20). Histologically benign lesions, such as aggressive fibromatosis, can share the same characteristics (Fig. 21)? The lack of specificity underscores the need for biopsy. Direct Invasion from Primary Tumor. Squamous cell carcinoma may extend outside the visceral space. Laryngeal and pyriform sinus tumors can grow laterally into the carotid space. Tumors of the posterior hypopharyngeal wall can invade the retropharyngeal space. Extension to the perivertebral space is uncommon. Chordoma, Vertebral Body Metastasis. These lesions may extend anteriorly in the perivertebral and retropharyngeal spaces. Radiologically, the tumor is centered on one or several vertebral bodies. Vascular Aneurysms of the cervical carotid and vertebral arteries are usually associated with atherosclerotic disease. Traumatic pseudoaneurysms are secondary to a disruption in arterial wall continuity with subsequent encapsulation of the periarterial hematoma. The diagnosis can be established with ultrasound, CT, or MR imaging including MR angiography. MR imaging examination of the brain is needed to evaluate the consequences of the arterial lesion. Thromboses of the internal jugular vein are associated with drug abuse, central venous catheterization, or head and neck cancer. During the acute phase the vein is enlarged and heterogeneous both on CT and MR imaging (see Fig. 10). In malignancy, the diagnosis can be hazardous if only one level is examined because acute venous thrombosis and metastatic lymph nodes with central necrosis and extracapsular spread may share the same characteristics and coexist (Fig. 22). In fact, recognition of the tubular nature of the vascular lesion makes the diagnosis easy. Pseudomass Tortuous Common or Internal Carotid Artery
Figure 16. Posterior neck lipoma. Contrast-enhanced axial CT scan. A, At the laryngeal level, the lipoma (arrow) occupies the posterior cervical space. There is a mass effect on the carotid space, and the internal jugular vein is hardly visible (arrowhead). B, The mass (arrow) extends into the thoracic inlet.
A tortuous common or internal carotid artery can manifest as a pulsatile mass in the carotid triangle at physical examination. It can also present as a submucosal mass displacing the pharyngeal posterior wall. At the level of the infrahyoid neck, palpation is not feasible and the pulsatile characteristic of the mass is overlooked. On contrast-enhanced CT scan, the diagnosis is straightforward, provided that iodine concentration is sufficient within the lumen (Fig. 23). At MR imaging the vessel typically shows the flow void pattern. MR angiography can help to convince the clinician, but is not indispensible.
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Figure 17. Retropharyngeal lipoma. Axial CT scans. The low attenuation well-marginated fatty mass extends along the retropharyngeal space from the oropharynx (A), through the neck (B)down to the mediastinum (C).
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Figure 18. Retropharyngeal lipoma. On the sagittal T1weighted view, the tumor (arrow) is disclosed as a high signal intensity mass extending in front of C2 and C6. Because both longus colli muscles are slightly off-midline, the retrophatyngeal mass is directly in contact with the anterior aspect of the vertebral bodies.
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Figure 19. Synovial sarcoma. Contrast-enhanced axial CT scan. Location in the posterior neck musculature of the perivertebral space indicates a mesenchymal origin.
Figure 20. Neck relapse from a parotid sarcoma. A, The axial Gd-enhanced fat suppressed T1weighted view shows a strongly enhancing mass that extends into the perivertebral space and carotid space and completely surrounds the left internal carotid artery (straight arrow). The involvement of the hypoglossal nerve (XII) in the carotid space is evidenced by abnormal signal intensity in ipsilateral tongue musculature (curved arrow). Encasement of the vertebral artery (arrowhead) is also displayed. Notice previous parotidectomy deformity (open arrow) with no abnormal contrast take up. B, The coronal view displays the superior-inferior extent of the tumor and shows invasion of the vertebral body of C2 (arrow).
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Figure 21. Aggressive fibromatosis. Contrast-enhanced axial CT scan. The mass shows intense and homogeneous enhancement. It seems well-circumscribed, but these lesions are known to be infiltrative and adherent, especially to vascular and neural structures.
Asymmetric Internal Jugular Vein The internal jugular vein is extremely variable at presentation. Internal jugular veins can be markedly asymmetric. A large, tubular, enhancing mass located lateral to the carotid should n o t be mistaken for a vascular tumor.
Vertebral Body Osteophyte, Cervical Rib, and Large or Asymmetric Transverse Process Vertebral b o d y osteophytes m a y manifest as a submucosal mass displacing the posterior pharyn-
Figure 22. Internal jugular vein associated with a metastatic lymph node. Contrast-enhancedaxial CT scan. The patient presented with a squamous cell carcinoma of the left pyriform sinus (not seen at this level). The thrombosed vein (straight arrow) and the jugulodigastric lymph node with extracapsular spread (curved arrow) share similar imaging features.
Figure 23. Tortuous common carotid artery. Contrastenhanced axial CT scan. The patient presented with a laryngeal squamous cell carcinoma (not seen at this level). At endoscopy, the physician reported bulging of the posterior pharyngeal wall. Imaging discloses a retropharyngeal enhancing vessel (straight arrow). It also shows a jugulodigastric metastatic lymph node (curved arrow).
geal wall. Cervical ribs and large or asymmetric transverse processes m a y present clinically as posterior cervical masses. Diagnosis is easy at CT or p l a i n films (Fig. 24).
Levator Scapulae Hypertrophy Levator scapulae hypertrophy is a consequence of radical neck dissection during w h i c h the sternocleidomastoid muscle is removed and the spinal accessory nerve is sacrificed leading to trapezius muscle atrophy. As a compensation, the levator scapulae muscle hypertrophies and can be per-
Figure 24. Vertebral body osteophyte. This mass presented at endoscopy as a submucosal mass displacing the posterior pharyngeal wall. Axial CT scan (bone algorithm) shows an osteophyte lying in the anterior portion of the perivertebral space.
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ceived clinically as a mass. The diagnosis at imaging is not always easy because the symmetric anatomic landmarks are lost. Absence of contrast enhancement and knowledge of the clinical history are the keys to diagnosis. SternocleidomastoidFibroma of Neonates
This is probably the most common lateral neck mass in neonates. It is also known as congenital torticollis and fibrornatosis ~ 0 l l i . IIt~ corresponds to a swelling or lump within the sternocleidomastoid muscle, often related to birth trauma. The diagnosis is based on physical examination. Brachial Plexopathies
Brachial plexopathies can be categorized as traumatic or nontraumatic, each of them accounting for approximately 50% of ~ases.2~ Traumatic Injuries
Accurate assessment of the site and extent of the injury is mandatory in injuries of the brachial plexus. Trauma may be due to traction, compression, penetrating injuries, local fractures, or disloc a t i o n ~ .Clinical ~~ and electrophysiologic studies are not very reliable.4 The determination of the exact location of the injury, extradural or intradural, directly affects the patient's prognosis and surgical strategy? CT myelography provides a reliable diagnosis of the extent of intradural damage? The accuracy of CT myelography is 85% using intraoperative findings as the gold standard? MR imaging is less effective to demonstrate intradural root avulsion (52% in Carvalho's et a14 series) because patients are not able to lie as still as required resulting in motion artifacts. Technical improvements, with shorter scan times, increased spatial resolution, and reduced cerebrospinal fluid artifacts, should overcome this inconvenience. MR imaging offers good depiction of the brachial plexus beyond the spinal foramen. When avulsion of a nerve root results in a pseudomeningocele it is visualized on axial or coronal T2-weighted images as a high signal intensity extra-arachnoid collection of cerebrospinal fluid around the missing nerve root. In the case of acute or subacute injury, a hematoma may be visible (Fig. 25). In infants with birth-related brachial plexus injury, CT myelography requires general anesthesia and can be replaced by MR imaging.* FSE TZ-weighted imaging can be used as a triage examination: the existence of a pseudomeningocele indicates the need for operation; in case of normal MR imaging findings, conservative management with close follow-up can be undertaken" Nontraumatic Lesions
Nontraumatic lesions include neoplasms, radiation fibrosis, brachial neuritis, nodal metastases,
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and symptomatic cervical ribs. Among primary neoplasms, schwannomas and neurofibromas are the most common lesions. These tumors tend to be well circumscribed with a markedly high signal intensity on T2-weighted images and strong conneurofibrosartrast e n h a n ~ e m e n t .z7~Although ~, comas tend to present with infiltrating margins (Fig. 26), no reliable criteria allow differentiation of benign from malignant peripheral nerve tumors with ~ e r t a i n t y The . ~ ~ brachial plexus may be directly invaded by primary tumors of the lung (Pancoast's tumor); bone; soft tissues in the neck; supraclavicular fossa; and upper part of the thorax. Coronal and sagittal MR imaging are particularly helpful to predict the resectability of the lesion. Lymph node metastases and intraspinal metastases may involve nerve roots. Radiation fibrosis may occur 5 to 20 years after therapy. It is unlikely with doses less than 60 Gy. There are no definite imaging criteria to differentiate recurrent or metastatic disease from postirradiation injury. CT-guided biopsy is recommended. Flaps and Posttherapeutic Changes
Cancer treatment usually requires surgical treatment, neck irradiation, or a combination of both techniques. Imaging plays an important role in the follow-up of these patients, who are often difficult to examine clinically.l,lo, 30, 3* After neck dissection and reconstructive surgery with myocutaneous flaps, CT or MR imaging can suggest the presence of tumor relapse or abscess (Fig. 27). After radiotherapy, contrast enhancement frequently corresponds to acute or subacute inflammatory changes and can be difficult to differentiate from tumor relapse (Fig. 28). Biopsy or sequential imaging follow-up permits one to establish the diagnosis. Comparison with baseline studies (usually CT) is recommended.Zo,30 IMAGING STRATEGIES
Clinical examination and endoscopy are essential in the selection of imaging techniques and strategy. Often, the patient presents with a neck mass with or without additional symptoms (pharyngeal discomfort, hoarseness). A malignant lesion (most often a squamous cell carcinoma) of the larynx, nasopharynx, oropharynx, hypopharynx, and oral cavity may be diagnosed by the physician and confirmed by pathology. The radiologist helps to define the exact extent of the primary lesion and should perform a complete lymph node survey. CT or MR imaging are the techniques of choice. If clinical examination of the superior aerodigestive tract is nonspecific, imaging is essential to establish the positive diagnosis by showing a true mass (versus a pseudomass). In addition, by demonstrating the exact space of origin of the lesion and its characteristics (CT density, MR imaging
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Figure 25. Brachial plexus trauma (one week). A, An axial view shows a pseudomeningocele, displayed as a collection of cerebrospinal fluid lateral to the thecal sac (white arrow). Increased signal intensity muscle corresponding to hematoma and edema is displayed outside the neural foramen (open arrow) and in the region of the anterior left scalene (curved arrow). 6, On the coronal view, the entire length of the left anterior scalene muscle has increased signal intensity (arrows). (Courtesy of C. Beigelman, MD, S. Lenoir, MD, HBpital Pitie-Salpetriere, France.)
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Figure 26. Brachial plexus neurofibrosarcoma. A, Contrast-enhanced axial CT scan. The illdefined, heterogeneous lesion invades the right perivertebral space and extends into the neural foramen (arrow). B, On the coronal Gd-T1-weighted view, the tumor seems embedded within the scalene muscles (open arrows), above the subclavian artery (straight arrow).
Figure 27. Post-therapeuticabscess. Total laryngectomy with myocutaneousflap transplant was performed for pyriform sinus squamous cell carcinoma. A, Contrast-enhanced axial CT scan shows an abscess (arrow) that extends into the fatty portion of the graft and opens into the skin. B, On fistulogram, the abscessed cavity (curved arrow) communicates with the base of the tongue (straight arrow) via an abnormally strictured pharyngeal canal (arrowhead).
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Figure 28. Postradiotherapy inflammation. The patient presented with an advanced hypopharyngeal tumor and was treated with external radiotherapy. An enhancing lesion is disclosed in the left perivertebral space (arrow). Biopsy did not disclose tumor recurrence.
signal, homogeneity or heterogeneity, contour, contrast enhancement), imaging can suggest the correct diagnosis. It can guide a biopsy or conversely prevent a procedure that may be dangerous (e.g., a hypervascular mass). Ultrasound can be used to confirm a clinical impression of a superficial, benign lesion (such as a lipoma). Cross-sectional imaging, however, is recommended if there is a suspicion that the lesion is deeply seated or invasive. In the case of a submucosal mass (i.e., deforming the pharyngeal-laryngeal wall), imaging can show the origin of the lesion and predict or affirm its nature (vertebral osteophyte, tortuous carotid artery). Specific clinical context can also orient the diagnosis. Fever and pain points to infection, nerve palsy to neural sheath tumor, and a bruit to chemodectoma. For infectious disease evaluation, CT is preferable because it allows one to recognize air, a salivary gland calculus, or a dental abscess. If there is a high suspicion of neoplasm, MR imaging is the preferred modality because it offers multiplanar, multiparameter information and identifies multicentricity or bilaterality (often associated with a familial syndrome). Specific clinical presentations focus the diagnosis on the thyroid or parathyroid glands. If a brachial plexopathy is suspected, MR imaging should be performed. The diagnosis of root avulsion can necessitate the use of myelo CT. ACKNOWLEDGMENTS The author would like to thank Amaud Chkron for the preparation of the photographs and Nicolas Denoisc for the preparation of the drawing (Fig. 1).
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Address reprint requests to Robert Sigal, MD, PhD Department of Imaging Institut Gustave Roussy 94805 Villejuif Cedex France e-mail: [email protected]