Imaging of radiation changes in the head and neck

Imaging of Radiation Changes in the Head and Neck By Lisa M. Tartaglino, Vijay M. Rao, and Deborah A. Markiewicz

options for treating T HEheadTHERAPEUTIC and neck tumors include surgery, radiation therapy, chemotherapy, laser excision, and immunotherapy. A team approach to select the most appropriate management has become the standard of practice. Radiation therapy is used for three different purposes: (1) primary curative radiotherapy; (2) radiotherapy and surgery in combination; and (3) radiotherapy alone for palliation. Modern radiotherapeutic techniques such as protective shielding and three-dimensional treatment planning minimize the amount of normal tissue within the treatment field. However, it is impossible to totally exclude normal tissues from the radiation field because a margin of normal tissue is required to cover microscopic disease and to allow for a buildup region to the full dose. The severity of the soft-tissue changes in the head and neck secondary to radiation depend on the total dose and the fractionation protocol used. Other factors such as the nutritional status of the patient, concomitant or prior chemotherapy, or surgery contribute in determining the response of the normal tissues within the radiated field. As a rule, some changes almost always occur after delivery of 7,000 centigray (cGy) to the region of interest. In this article, imaging of the postradiation changes involving the orbit, facial skeleton, sinuses, salivary glands, soft tissues of the neck, larynx, and pharynx is discussed.

lacrimal gland can be visualized on computed tomography (CT) and magnetic resonance imaging (MRI). The lacrimal gland behaves as other salivary gland tissue. In the acute period, the gland may swell. Secretions are depressed, which can lead to the dry-eye syndrome. The abnormally thick mucoid secretions may predispose to infection. Imaging studies alone may not be able to separate infection from postradiation changes. As time progresses, the lacrimal gland may decrease in size becoming more fibrotic and dense. Enhancement may be present on both CT and MRI. In general, when radiation doses are 5,000 cGy or higher, 2 severe dry-eye syndrome may develop. Keratitis, corneal ulcerations, and scarring occur with subsequent loss of vision. 3 Cataracts may further decrease vision. With increasing radiation dose, cataracts will appear earlier and with a higher incidence, z Posterior complications include the following effects: (1) radiation retinopathy consisting of hemorrhages, vascular occlusions, and exudates; (2) radiation-induced optic neuropathy to the optic nerve or chiasm; (3) myositis; (4) cranial nerve dysfunction; 1 and (5) acquired empty sella syndrome. 4 Retinal injury typically occurs 11/2to 3 years after high-dose radiation with visual deterioration progressing over months. Radiation retinopathy is also more common at doses above 5,000 cGy total dose. 1,3 Although the retina itself is relatively resistant to radiation damage,

ORBIT Orbital complications after therapeutic radiation can be divided into those lesions extending from the lens anteriorly and those posterior to the lens. 1 Visual loss may occur after radiationinduced lesions in both areas as well as secondary to tumor recurrence. Those lesions defined as anterior include the following: (1) irritation; (2) erythema and edema of the eyelid; (3) lacrimal gland and duct stenosis or obstruction with or without epiphoria (overflow of tears); (4) xerophthalmia (dry eye); (5) conjunctivitis; (6) keratitis and corneal ulceration; and (7) cataracts. 1 For the purposes of this article, only anterior lesions related to the Seminars in Roentgenology, Vol XXIX, No 1 (January), 1994: pp 81-91

ABBREVIATIONS CT, computed tomography; MRI, magnetic resonance imaging; ORN, osteoradionecrosis; RON, radiation-induced optic neuropathy

From the Department of Radiology, Thomas Jefferson University Hospital, and the Department of Radiation Oncology, Universityof Pennsylvania School of Medicine, Philadelphia, PA. Address reprint requests to Vljay M. Rao, MD, Department of Radiology, Thomas Jefferson University Hospital, 132 S. lOth St, Philadelphia, PA 19107. Copyright 9 1994 by W.B. Saunders Company 0037-198X/94/2901-000955. 00/0 81

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the retinal end-arteries are not. As the endothelium is damaged, acute vascular occlusions occur. "Cotton wool" spots and flame hemorrhages are seen on ophthalmoscopic examination. Progression to microaneurysms, neovascularity, retinal telangiectasias, and hard exudates leads to retraction retinal detachment, vitreous hemorrhage, and optic nerve atrophy. 1,3 These latter, more chronic changes are visualized on CT and MRI. CT scanning will show homogenous increased density crescentically inside the posterior aspect of the globe or involving the vitreous chamber. With a retinal detachment, there may be a small indentation at the optic disc. On MRI, the hemorrhage is usually seen as increased signal intensity on Tl-weighted images. T2-weighted images are more variable depending on the age of the hemorrhage. With chronicity, the hemorrhage will become less uniform in appearance, and calcification (Fig 1) may be observed. Atrophy of the globe and optic nerve may be present. Radiation-induced optic neuropathy (RON) causes a rapid deterioration in vision over days to weeks. The latent period postradiation varies from 6 to 192 months with a median of 12 months. 5 RON has been reported after radiation for sellar/parasellar tumors and intracranial meningiomas as well as for radiation given to orbital, sinus, and pharyngeal tumors.I, 3,5-8 Visual loss may be complete and may occur in the other eye within weeks to months. 8,9 Initially, the optic disc may appear normal, especially if the chiasm or posterior optic nerve is involved. If it is pale, the cause is most likely from previous compression from the original tumor. However, within 6 to 8 weeks, the disc will uniformly turn pale. 8,9 Pathologically, RON is comparable with the delayed cerebral radionecrosis noted intracranially with an etiology that is probably vascular in origin. Thickened blood vessels are present with evidence of fibrinoid necrosis, hemorrhage, and gliosis. Areas of ischemic demyelination and astrocytic proliferation also are typically found. 9 MRI is the imaging modality of choice when RON is suspected (Fig 2). Thin-section axial and coronal Tl-weighted images of the orbit, precontrast and postcontrast, are ideal. Fat suppression on the postgadolinium images is suggested to visualize the intraorbital portion of

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Fig 1. Axial CT scan through the left midorbit in a patient who received radiation for left maxillary sinus carcinoma 10 years prior shows a small globe. Along the posterior aspect of the globe is a crescentic area of increased density with focal calcification consistent w i t h a previous retinal detachment (arrows) secondary to the radiation.

the nerve. Enhancement of the optic nerve and/or chiasm with or without swelling may be observed in the acute to subacute stage. 6-8 It is possible that the enhancement may correlate with 'the activity of the lesion. 7 Late findings often show absent enhancement and atrophy. Although T2-weighted images would be expected to show increased signal intensity within the optic nerve, this is not reliably observed. Possible reasons are as follows: (1) adjacent

Fig 2. Coronal Tl-weighted MR! postcontrast with fat suppression in a patient 14 months postradiation with presenting symptoms of progressive visual loss over a week. Note the enhancement of the right optic nerve (arrows) compared with the left consistent with radiation-induced optic neuritis.

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cerebralspinal fluid signal may obscure the lesions and/or (2) relative decreased spatial resolution and signal to noise on standard T2weighted spin-echo pulse sequences. 7 CT scans are usually normal unless there is gross enlargement of the optic nerve. R O N must be differentiated from acquired empty sella syndrome as a cause of visual loss. This can occur after surgery and/or radiation for a sellar tumor. The chiasm may be affected by arachnoid adhesions with or without displacement and retraction of the chiasm inferiorly into t h e sella. 4,9 Prognosis is better than RON, and surgery may be curative. On MRI and CT, an enlarged sella turcica will be noted without evidence of recurrent tumor. The chiasm may be deformed and inferiorly displaced. The extraocular muscles can be affected by radiation although this is usually not symptomatic. Early findings include swelling and inflammation of the involved muscle (Figs 3A and B). Contrast enhancement may be present. In the more chronic stage as fibrosis develops, the muscles become atrophic. Various types of postradiation sarcomas have been described in the literature. There is an unusually high incidence in patients with the hereditary form of retinoblastoma. 1~ A radiation-induced sarcoma may be suspected when it occurs in an area previously irradiated. The latency period is usually very long with a range among all sarcomas of 5 to 30 years.l~ SKELETAL STRUCTURE

Radiation to the head and neck affects the adjacent skeletal structures in several ways. Osteoradionecrosis, and more rarely, radiationinduced sarcomas, have been described primarily affecting the mandible. The adjacent clivus and cervical spine undergo typical changes in the marrow that persist indefinitely. Sinuses and mastoid air cells may develop secondary mucosal thickening. Mucoceles can develop in the paranasal sinuses. In children, the effects can be particularly deforming because, with survival, hypoplasia of the jaw, hemiface, and orbit may occur lz secondary to alterations in growth. As with all areas, radiation effects will be altered by both the fractionation and total dose, the type of radiation, the type of tissue involved, as well as individual variation. Normal marrow response to radiation therapy

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Fig 3. Contrast-enhanced CT scan through the orbit in a patient who is status post resection and radiation 2.5 months earlier for a leionlyoma involving the right lateral orbit. {A) Axial scan through the orbit shows enlargement of the lateral rectus muscle (closed black arrows). (B) Coronal image through the miderblts shows enlargement of beth the lateral (closed black arrows) and superior (open black arrows) rectus muscles. Although the lateral rectus may be enlarged secondary to surgery or radiation, the superior rectus was believed to be enlarged secondary to radiation primarily.

can be observed as early as 2 weeks on short-T1inversion-recovery MRI with doses as low as 1,500 cGy. Increased signal intensity at this time is believed to represent early marrow necrosis and edema. 13 Spin-echo Tl-weighted images start to show mottled signal intensity at approximately 3 weeks corresponding to a mixture of fibrosis and fatty infiltration. Late marrow changes (greater than 6 weeks) may show one of two patterns. Diffuse fatty infiltration may be noted with diffuse increased signal on T1weighted images corresponding to the radiation field (Fig 4). Alternatively, central marrow fat

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Fig 4. Sagittal Tl-weighted MRI through the cervical spine in a patient w h o received radiation I year earlier for carcinoma of the tongue shows diffuse increased signal intensity in the marrow of C2-C4 compatible w i t h diffuse f a t t y infiltration. Note the sharp transition to the more normal signal intensity of the marrow in the lower vertebral bodies, This corresponds to the edge of the radiation field.

surrounding the basivertebral vein with peripheral hematopoietic marrow may be seen as a bandlike pattern of central bright signal bordered by areas of intermediate signal. ~3 The latter pattern appears particularly common in younger patients. Osteoradionecrosis (ORN) occurs secondary to a combination of damage to the vascular

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supply as well as direct injury to osteoblasts and osteoclasts. ~4Consequently, healing, growth, repair, and resistance to infection are all impaired. Because bone turnover is slow, the full extent of necrosis and radiographic changes may not be evident for over a year, 15,a6although MRI can show marrow changes in a matter of weeks, a3 O R N can occur at any time postradiotherapy, and the involved bone is susceptible to developing O R N throughout life. 16,17Radiation effects also decrease saliva production from the salivary glands. This in turn predisposes the patient to development of dental caries. Subsequent infection can occur in this setting, with tooth extraction or with other trauma, and is unusually common in O R N of the mandible. 16-18 The typical appearance of O R N on CT (Fig 5A) is that of focal areas of demineralization, disorganization of the trabecular pattern, cortical thickening, and areas of sclerosis. 19Pathological fractures (Fig 5B) often are present at the juncture of dead and partially viable bone. 16 Sequestra are notably unusual. The appearance may be difficult to differentiate from tumor recurrence or radiation-induced sarcoma. However, a narrow zone of transition, slow progression, and absence of a soft-tissue mass all favor ORN. 15,18A9Periosteal reaction and a soft tissue mass are distinctly uncommon in the uncompli-

Fig, 5. Bone windows from an axial CT scan in a patient w h o received radiation for tongue carcinoma 18 months earlier demonstrates characteristic findings of osteoradionecrosis (ORN). (A) Note the mixed density of the right mandible with thickened cortex (short white arrows) and disorganization of the trabecular pattern, (B) A fracture (black arrow) is visible at the transition zone of the affected bone and more normal bone. Periosteal reaction is also present (arrowheads).

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cated case of ORN but may occur when complicated by infection or fracture. The MRI of ORN involving the mandible or maxilla has not been described in the literature to our knowledge. It is expected that changes may resemble osteonecrosis of other etiologies. Acutely, Tl-weighted images show decreased signal intensity with corresponding increased signal on T2-weighted images. This probably represents edema. 2~ In later stages, low signal persists on Tl-weighted images, whereas T2weighted images may show mixed signal intensity corresponding to areas of edema and fibrosis.21 With chronicity, focal areas of fat may be deposited, 22 which on Tl-weighted images will be of increased signal. Fibrosis and areas of sclerosis also occur corresponding with hypointense signal on both T1- and T2-weighted images. 21 Postradiation sarcoma of bone can arise within the treatment area either in previously normal bone or in bone that contained the underlying lesion treated with radiation. The most common tumors are either osteosarcoma or fibrosarcoma. 11,23,24In Huvos' series, 5.5% of osteosarcomas are a result of previous therapeutic or incidental irradiation.25 There is a long latent period with a range of 2.75 to 55 years.23 Most patients are symptomatic with pain and swelling. In the mandible and maxilla, a previously irradiated lesion of fibrous dysplasia appears to have an unusually high propensity to later develop a sarcoma. 23 Most sarcomas regardless of the type tend to be high-grade lesions, u The CT appearance usually shows a softtissue extraosseous component with associated bone destruction. Bone expansion, periosteal reaction, and tumor matrix mineralization can occur. Tumor matrix mineralization appears to be more common in head and neck sarcomas for unknown reasons. 24 CT appears to be better than MRI for the evaluation of cortical bone and calcification, whereas MRI is better for evaluation of marrow spaces and the soft-tissue component. 26 Marrow extension may be best visualized on Tl-weighted MRI because of the contrast between the relatively hypointense signal of tumor and edema compared with the marrow. Gadolinium-enhanced images can separate tumor from edema and necrosis. T2-

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weighted images are most useful for evaluating soft-tissue extension and cortical involvement.27 Finally, the paranasal sinuses and mastoid air cells are unusual skeletal structures in that they are lined by mucosa. After radiotherapy, the mucosa may become inflamed and secondarily fibrose. Chronic inflammation (Figs 6A and 6B) may occur, and mucoceles (Figs 7A and 7B) can form of the paranasal sinsues. 28 SOFT TISSUES OF THE NECK

Commonly encountered postradiation changes in the soft tissues of the neck during imaging studies include skin thickening and stranding of subcutaneous fat (Figs 8A and 8B). Bornstein and colleagues reported a significantly higher frequency of stranding of subcutaneous fat in areas distant from the tumor in patients after radiation therapy than before such treatment. 29 Similar changes have been described in the chest wall after radiation therapy for breast carcinoma. 3~ The frequency of stranding of fat in the deep cervical spaces of the parapharyngeal and perivascular regions is also higher in patients who had received radiation treatment. However, these effects cannot be reliably distinguished from postsurgical or tumor effects.29 Skin thickening can be secondary to radiation, surgery, or tumor spread. Abnormal skin thickening at sites distant from tumor and surgery usually are attributed to radiation. Skin ulceration and fibrosis due to radiation are estimated to occur within 5 years in 1% to 5% of patients after 5,500 cGy and in 25% to 50% of patients after 7,000 cGy.31 It is generally accepted that preoperative radiation is associated with an increased risk of postsurgical wound complications such as infection, flap elevation, necrosis, and fistulae formation. Orocutaneous or pharyngocutaneous fistulae result from accumulation of saliva under the neck-skin flaps with the majority appearing within 3 weeks of surgery. Radiation-induced myopathic changes indude atrophy, fibrosis, and necrosis. Acute radiation necrosis of skeletal muscle may occur within hours of exposure to a single high dose in the range of 50,000 and 100,000 cGy.32 On the other hand, delayed changes may occur 2 to 3 months after therapeutic doses (Figs 9A and

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histology, a variety of appearances including fragmentation of myocytes, focal necrosis, and areas of atrophic fibers are noted. 32 Redvanly and colleagues reported a case of radiation necrosis of the sternocleidomastoid muscle mimicking necrotic adenopathy in a patient with advanced squamous cell carcinoma of the pyriform sinus who received 7,590 cGy in 32 fractions to the region of interest after extensive surgery. 33 Patients receiving radiation therapy for carcinoma of nasopharynx, oropharynx, or tonsil may develop fibrosis of the pterygoid muscles and present with trismus (Fig 10). Vascular injury can also affect large vessels

Fig 6. Radiation-induced mastoiditis in a patient w h o received radiation for a chondrosarcoma (asterisk) at the base of the skull, (A) Preradiation axial CT scan through the base of the skull shows a destructive mass (asterisk) invading the base of the skull, Note the clarity of the mastoid air cells. (B) Postradiation scan showed opaciflcation of the mastoid air cells, Other images (not shown) demonstrated sclerosis compatible with chronic inflammation, The mass did not change over this time period,

9B). Atrophy of the muscle with fat replacement is easily detected by CT or MRI. The myopathic changes are caused by decreased blood supply from radiation effects on the small arterioles. By

Fig 7. Axial CT scans preradiation and postradiation for squamous cell carcinoma of the nasopharynx. (A) Preradiation scan of the maxillary sinuses shows no evidence of sinus inflammatory disease. (B) Postradiation scan in the same patient 3 years later shows complete opacification of the maxillary sinuses bilaterally with expansion of the left maxillary sinus compatible w i t h evolution of a mucocele (arrows).

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tion therapy.34,35 The atherosclerotic plaques occur diffuselywithin the radiation field often in a pattern atypical for naturally occurring plaques that generally are focal and located at the bifurcations.34 Thrombosis of the vessels also can occur secondary to intimal injury and fibrosis. This can occur earlier within months and in the absence of atherosclerosis.36 LARYNX AND PHARYNX

Fig 8. Axial contrast-enhanced CT scan preradiation and postradiation for squamous cell carcinoma of the hypopharynx. (A) The preradiation scan of the neck shows deformity of the right lateral and posterior pharyngeal margin (black arrows) due to the squamous cell carcinoma. Also note a moderate-sized right necrotic node (asterisk) with low density center and an enhancing rim. (B) The postradiation scan shows stranding of the subcutaneous fat diffusely and thickening of the platysma muscle (black arrowheads). The epiglottis is now thickened, and soft-tissue density obliterates the vallecula bilaterally. Also note increased density, enhancement, and decreased size of the submandibular glands bilaterally (asterisk). In the interim, the necrotic node has enlarged and t w o additional contralateral necrotic nodes are seen on the left.

included within the radiation port from the common carotid (Fig 11) or vertebral arteries to the circle of Willis. Accelerated atherosclerosis is the most common abnormality seen and may present with transient ischemic attack or strokelike symptoms years after undergoing radia-

The first effect of radiation that is encountered early in the course of treatment is mucositis, usually after delivery of 2,000 to 3,000 cGy. This may progress to edema of mucosa and submucosa as the treatment continues, which may lead to diffuse thickening and increased density of the larynx. These changes are fairly pronounced on CT scans and are often difficult to differentiate from tumor itself. Radiationinduced edema is due to accumulation of excess interstitial fluid secondary to blocked vascular and lymphatic outflow in addition to increased vascular permeability. It is most pronounced around 2 to 4 weeks after the termination of the radiation treatment. This edema gradually diminishes in the next few weeks as the vascular permeability decreases and new capillaries form. Diffuse laryngeal edema involving the epiglottis, aryepiglottic folds, and false cords secondary to lymphedema may persist up to 6 months after the completion of high-dose radiation therapy. 37,38 Supraglottic edema persisting for 2 to 7 years after radiation also has been reported on MR imaging.39 Persistent edema after 6 months poses a difficult problem of differentiating postradiation edema from recurrent or residual laryngeal carcinoma. At this time, the otolaryngologist may be suspicious of recurrent or residual carcinoma because of hoarseness of the voice, and the clinical examination often is limited due to swelling of the larynx. CT scans show generalized thickening of the supraglottic soft tissues usually with narrowing of the airway and increased density in the pre-epiglottic and paralaryngeal spaces (Figs 12A and 12B). These changes are usually diffuse, symmetric, and do not create focal bulky masses. The edema may involve the cricoarytenoid joints with resultant restriction of the vocal cord motion. Frequently, when residual tumor is present, it is usually in the form of tiny nests

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Fig. 9, Prevertebral myopathy in a patient who is status post laryngectomy and radiation therapy. (A) Contrast-enhanced axial CT shows marked enhancement and enlargement of the prevertebral muscles (arrows). (B) Axial Tl-weighted spin echo image (TR 800 Msec, TE Z0 Msec) with gadolinium also demonstrates enhancement of the prevertebral muscles (arrows).

of cells inconsistently distributed throughout the site of the original tumor and requires multiple biopsies for the diagnosis. 4~ Furthermore, focal masses seen by CT in the postradiated larynx, although suspicious for tumor, may represent areas of reactive fibrosis. There are no specific CT criteria to differentiate tumor from such postradiation changes. 37 To date, there is paucity of literature on the utility of MRI in such differentiation. There are scanty

reports in the literature that have explored the potential of MRI in differentiating radiation fibrosis from recurrent or residual tumor. Mature radiation fibrosis tends to demonstrate low signal intensity on both T1- and T2-weighted spin-echo images. The signal intensity of the tumor is generally higher than that of muscle. On the other hand, acute radiation changes, infection, and hemorrhage may show signal intensity similar to that of tumor and further

Fig 10. Axial contrast-enhanced CT scan in a patient with trismus after radiation therapy for nasopharyngeal carcinoma. There is nonenhancing soft-tissue mass (arrows) in the right masticator space consistent with fibrosis of the media[ pterygold muscle confirmed by biopsy. Note obliteration of the parapharyngeal fat.

Fig. 11. Axial contrast-enhanced CT scan in a patient who received radiation for carcinoma of the larynx shows complete thrombosis of the left common carotid artery (arrows).

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Fig 12. Postradiation contrast-enhanced axial CT scans for carcinoma of the larynx. (A) Note epiglottic thickening (white arrows) and stranding of the subcutaneous fat end platysma. (B) Scan at the level of thyroid cartilage demonstrates increased soft tissue density of the supraglottic larynx with compromise of the airway (black arrow), Also note edema of the sternocleidomastoid and strap muscles bilaterally.

diminish the reliability of MRI in this differentiation. 41 The use of gadolinium may not improve the specificity either because enhancement is nonspecific and may be seen with inflammation, early postradiation changes, postoperative scar, and recurrent or residual tumor. MRI spectroscopy theoretically has potential and needs to be explored. If severe changes persist after 6 to 12 months after completion of radiation therapy, the index of suspicion for underlying tumor increases. Surgeons are often reluctant to perform multiple laryngeal biopsies because of the risk of precipitating chrondronecrosis. Complications such as fibrosis, scarring, and retraction are somewhat unusual in the larynx but do present with a characteristic CT appearance. The hyoid bone and thyroid cartilage are normally not both seen together on the same CT section unless the neck is extremely flexed. However, postradiation scarring and fibrosis in the larynx may result in shortening of the thyrohyoid and cricothyroid membrane and lead to this deformity. In addition, fibrotic changes at the anterior and posterior commissure may result in fixation of the vocal cords in a paramedian position. The ipsilateral pyriform sinus may be dilated secondary to anteromedial fixation of the arytenoids and medial retraction of the aryepiglottic folds. The density of the vocal

cords and the intrinsic soft tissues of the larynx may be decreased secondary to muscle atrophy and subsequent replacement by fat and fibrosis. 37 The radiated larynx has a predilection to chondronecrosis because of its decreased vascular supply. Chondronecrosis most frequently involves the epiglottis, which shows thickening and increased soft-tissue density in the preepiglottic space. This can mimic residual or recurrent tumor. The arytenoids are the second most common cartilage to be involved by chondronecrosis. Characteristically, soft-tissue fullness is seen surrounding the arytenoids. Chondronecrosis of thyroid cartilage results in paramedian weakening of either one or both laminae with inward bowing. Advanced changes lead to obvious fragmentation with compromise of the supraglottic airway. Loss of integrity of the cricothyroid membrane may occur with collapse and overlap of the thyroid cartilage and the cricoid lamina. Associated supraglottic soft tissue thickening makes it indistinguishable from recurrent carcinoma by CT (Fig 13). SALIVARY GLANDS

The major and minor salivary glands are extremely sensitive to radiation. With doses as little as 1,000 to 2,000 cGy, signs and symptoms of mucositis will appear at 1 to 3 weeks. 42

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lobulated metastatic masses: 4,45 A direct relationship between radiation dose, fraction size, and fibrosis also is documented. 44Mature radiation fibrosis tends to show signal intensity equal to or less than that of muscle on T2-weighted images. Lack of enhancement with gadolinium favors mature fibrosis but enhancing soft tissue may represent neoplasm or immature and vascularized scar tissue. LUNG APICES

Fig. 13. Axial CT through the larynx of a patient who received radiation for carcinoma of the larynx shows deformity of the cricoid cartilage (arrows) consistent with chondronecrosis,

Permanent severe dryness of the mouth (xerostomia) may occur leading to altered taste, dental caries, soft-tissue ulceration, and osteoradionecrosis of the mandible. Xerostomia can be reduced or prevented if 50% or more of the parotids can be excluded from the radiation field. 42The soft-tissue density and enhancement of the salivary glands may increase (Figs 8A and 8B) with doses greater than 4,500 cGy.43 Later changes reported of the major salivary glands include involution and fatty replacement. 37 BRACHIAL PLEXUS NEUROPATHY

Differentiating radiation-induced brachial neuropathy from neoplastic infiltration of the brachial plexus can be quite difficult. Nonenhancing streaky soft-tissue densities in the region of brachial plexus suggest postradiation fibrotic changes compared with well-defined

Radiation-induced changes in the lung apices are frequently encountered in patients with treated head and neck tumors because this region is usually within the radiation field for lower neck disease. Characteristic CT findings of early radiation-induced change include ground glass opacity or patchy consolidation, which correspond to interstitial pneumonitis. Progression to discrete consolidation due to early fibrosis and incomplete contraction followed by solid consolidation due to mature fibrosis can be demonstrated by serial CT imaging. 46 CONCLUSION

It is apparent that both normal and abnormal tissues are affected by radiation treatment to the head and neck. Although certain changes are easily attr.ibuted to radiation effect, many lesions still can be difficult to differentiate from tumor recurrence. With the rapid progression of imaging technology, particularly in MRI applications, it is hoped that we will better separate these two processes. In addition, continued advances in radiotherapeutic techniques and treatment planning will be expected to decrease adverse effects to normal tissues in the future.

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