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Lateral neck mass in a child
Radiologic-Pathologic Correlation Arvin E. Robinson, MD, Editor
Lateral N e c k M a s s in a Child Bassem A. Georgy, MD 1, Byron G. Brogdon, MD 1, Randall W. Powell, MD 2, Judy Ann Curtis King, MD, PhD 3
CLINICAL PRESENTATION
A 5-year-old boy with no prior history presented with a left neck mass. The patient had no fever or any signs of obstruction. Thyroid function was normal. No significant findings were noted on laboratory or physical examination. RADIOLOGIC
PRESENTATION
An admission chest radiograph showed a soft-tissue fullness in the left side of the neck that was causing minimal deviation of the trachea to the opposite side (Fig. 1). Ultrasound examination (Fig. 2) defined a hypoechoic
mass measuring approximately 4.5 x 2 cm in diameter, separate from the thyroid gland, which appeared to be normal. The left common carotid artery and jugular vein could be identified on either side of the mass. Diagnostic consideration at this point included a neurogenic tumor or a cystic neck mass with thick fluid inside. Computed tomography scans (Fig. 3) showed a well-defined, rimenhancing cystic mass with an average attenuation of 30 Hounsfield units. The mass was located in the carotid sheath between the left carotid artery and the left internal jugular vein and extended from the level of the mandible into the superior mediastinum. RADIOLOGIC
DIAGNOSIS
The radiologic diagnosis was a cystic structure on the left side of the neck with thick fluid inside. The most c o m m o n lesions are cystic hygroma or brachial cleft cyst. CLINICAL COURSE AND PATHOLOGIC
FIGURE 1. Close-up of frontal chest radiograph shows the left-sided neck mass displacing the trachea to the right.
At surgery, a well-encapsulated mass was identified under the left sternocleidomastoid muscle with close proximity to the phrenic nerve. Using blunt dissection, the mass (16.5 × 5 × 2.5 cm, containing 50 ml of y e l l o w orange fluid) was completely freed and easily pulled from the mediastinum through the thoracic inlet (Fig. 4). Microscopic examination showed thymic tissue in the wall with fibrosis, cholesterol granulomas, chronic inflammation, and calcification. The cyst wall was lined by squamous cells (Fig. 5).
From the Departments of 1Radiology, 2Surgery, and 3pathology, University of South Alabama Medical Center, Mobile, AL. Address reprint requests to B. G. Brogdon, MD, University of South Alabama Medical Center, 2451 Fillingim St., Mobile, AL 36617. Received and accepted for publication May 30, 1995. Acad Radiol 1995;2:1026-1028
© 1995, Association of University Radiologists
1026
FINDINGS
Vol. 2, No. 11, November 1995
LATERAL
NECK MASS
IN A C H I L D
FIGURE 2. Transverse sonograms locate the well-defined hypoechoic mass, separate from the thyroid (THY), between the left common carotid artery (CCA) and left jugular vein (J VEIN).
A
B
A
B
FIGURE 3. Selected contrasted computed tomography sections show the cystic mass (m) in the left carotid sheath between the artery (a) and vein (v) as it extends from just beneath the angle of the jaw to deep within the mediastinum.
C
D
FINAL DIAGNOSIS The final diagnosis was a cervical thymic cyst. DISCUSSION Embryologically, the thymus develops as sacculations from the ventrolateral aspect of the third pharyngeal pouch during the 6th week of life [1]. The dorsal wing of the same pouch gives rise to the inferior parathyroid glands. By the end of this week, the connection of the thymic primordia with the pharyngeal pouches is severed. Each primordium elongates caudally and medially as a tubular structure (thymopharyngeal tract), which soon begins a process of obliteration. By the 8th week
of life, the bilateral thymic primordia fuse in the midline and start to slide down under the sternum in the superior mediastinum. Speer [2] suggested five mechanisms for the pathogenesis of cyst formation within the thymus: embryologic remnants in the neck, sequestration products, neoplastic process, degeneration of Hassall's bodies, or mesenchymal elements. Fahmy [3] attributed the development of thymic cysts to the presence of sequestrated remnants within and adjacent to the gland across the line of descent. The site of the classic branchial cyst along the line of the thymopharyngeal tract, and the similarity of its epithelial lining to that of the thymic cyst, supports the idea that they are both derived from 1027
GEORGY
E T AL.
FIGURE 4. Intraoperative photograph shows the mass being pulled from the mediastinum through the thoracic inlet.
FIGURE 5. Light micrograph of the cyst wall with thymic tissue (T). A segment of lining composed of squamous cells is indicated (arrow). (Hematoxylin and eosin staining, original magnification, x16)
Vol. 2, No. 11, November 1995
cervical triangle [4] either anterior t o or deep to the sternomastoid muscle [5]. The fact that cervical thymic cysts are usually found within the carotid sheath may permit differentiation from large cysts of other origins [6]. Fewer than 100 cases of cervical thymic cysts have been reported in the literature. The cysts occur more frequently in males than females and in the left rather than right side of the neck [3, 5, 7]. Approximately 50% of the reported cases are connected to the mediastinum with a fibrous band [3]. The majority are multicystic [51. Cyst fluid may be clear, yellow, brown, green, or even purulent. Free-cholesterol crystals may be found in the fluid or embedded in the wall [8]. Normal thymic tissue with Hassall's corpuscles are often found within the cyst wall [8]. The cyst lining may be columnar, cuboidal, or stratified squamous epithelium [4]. The prognosis is excellent after surgical removal of the cyst [1]. Malignant transformation has been reported in one case [9]. The differential diagnosis of lateral neck mass in a child includes cystic hygroma, lymphangioma, branchial cleft cyst, lymphadenopathy, thyroid pathology, or thyroglossal cyst. Other rare lesions include dermoid cyst, teratomas, cystic degeneration of thymoma, cervical myelomeningocele, external laryngeal diverticulum, or cervical echinococcal hydatid cyst. Only thymic cysts and branchial cysts occur within the carotid sheath. In summary, cervical thymic cysts are rare. They arise from the remnant of the thymopharyngeal tract in the anterior triangle during the first decade of life; the prognosis after surgery is excellent. They should be included in the differential diagnosis of cystic neck masses in the appropriate clinical setting, particularly if the cysts lie between the carotid artery and internal jugular vein within the carotid sheath. REFERENCES
the same vestigial structure. Both lesions represent a variant of the same developmental anomaly in different age groups [3]. Two thirds of the cases of thymic cyst present during the first decade of life, whereas branchial cysts are the most c o m m o n in the third decade, w h e n more than 60% occur; only 2% are found in the first decade of life. Typically, the anatomic location is in the path of descent of the thymopharyngeal tract in the neck and in the mediastinum. In the neck, it is usually observed along a line extending from the angle of the mandible to the manubrium sterni, particularly in or near the anterior
1028
1. Tovi F, Mares AJ. The aberrant cervical thymus: embryology, pathology and clinical implications. Am J Surgery 1987;136:631-637. 2. Speer FD. Thymic cyst. NY Med Coil Flowers Hosp Bull 1938; 1:142. 3. Fahmy S. Cervical thymic cysts: their pathogenesis and relationship to branchial cysts. J Laryngol Oto11974;88:47-60. 4. Rosai J, Levine GD. Tumors of the thymus. In: Atlas of tumor Pathology (2nd series). Washington, DC: Armed Forces Institute of Pathology, 1987:207-211.
5. Lyons 1-, Dickson JAS. Varied s. cervical thymic cyst. J Pediatr Surg 1969; 24:241-243. 6. Levine C. Cervical presentation of a large thymic cyst: CT appearance. J Comput Assist Tomogr 1968;12:656-657. 7. Guba AM, Adam AE, Jaques DA, Chambers RG. Cervical presentation of thymic cysts. Am J Surgery 1978;136:430-436. 8. Reiner M, Beck AR, Rybak B. Cervical thymic cyst in children. Am J Surgery 1980; 139:704-707. 9. Leong ASY, Brown JH. Malignant transformation in a thymic cyst. Am J Surg Patho11984;8:471-475.
Lateral N e c k M a s s in a Child Bassem A. Georgy, MD 1, Byron G. Brogdon, MD 1, Randall W. Powell, MD 2, Judy Ann Curtis King, MD, PhD 3
CLINICAL PRESENTATION
A 5-year-old boy with no prior history presented with a left neck mass. The patient had no fever or any signs of obstruction. Thyroid function was normal. No significant findings were noted on laboratory or physical examination. RADIOLOGIC
PRESENTATION
An admission chest radiograph showed a soft-tissue fullness in the left side of the neck that was causing minimal deviation of the trachea to the opposite side (Fig. 1). Ultrasound examination (Fig. 2) defined a hypoechoic
mass measuring approximately 4.5 x 2 cm in diameter, separate from the thyroid gland, which appeared to be normal. The left common carotid artery and jugular vein could be identified on either side of the mass. Diagnostic consideration at this point included a neurogenic tumor or a cystic neck mass with thick fluid inside. Computed tomography scans (Fig. 3) showed a well-defined, rimenhancing cystic mass with an average attenuation of 30 Hounsfield units. The mass was located in the carotid sheath between the left carotid artery and the left internal jugular vein and extended from the level of the mandible into the superior mediastinum. RADIOLOGIC
DIAGNOSIS
The radiologic diagnosis was a cystic structure on the left side of the neck with thick fluid inside. The most c o m m o n lesions are cystic hygroma or brachial cleft cyst. CLINICAL COURSE AND PATHOLOGIC
FIGURE 1. Close-up of frontal chest radiograph shows the left-sided neck mass displacing the trachea to the right.
At surgery, a well-encapsulated mass was identified under the left sternocleidomastoid muscle with close proximity to the phrenic nerve. Using blunt dissection, the mass (16.5 × 5 × 2.5 cm, containing 50 ml of y e l l o w orange fluid) was completely freed and easily pulled from the mediastinum through the thoracic inlet (Fig. 4). Microscopic examination showed thymic tissue in the wall with fibrosis, cholesterol granulomas, chronic inflammation, and calcification. The cyst wall was lined by squamous cells (Fig. 5).
From the Departments of 1Radiology, 2Surgery, and 3pathology, University of South Alabama Medical Center, Mobile, AL. Address reprint requests to B. G. Brogdon, MD, University of South Alabama Medical Center, 2451 Fillingim St., Mobile, AL 36617. Received and accepted for publication May 30, 1995. Acad Radiol 1995;2:1026-1028
© 1995, Association of University Radiologists
1026
FINDINGS
Vol. 2, No. 11, November 1995
LATERAL
NECK MASS
IN A C H I L D
FIGURE 2. Transverse sonograms locate the well-defined hypoechoic mass, separate from the thyroid (THY), between the left common carotid artery (CCA) and left jugular vein (J VEIN).
A
B
A
B
FIGURE 3. Selected contrasted computed tomography sections show the cystic mass (m) in the left carotid sheath between the artery (a) and vein (v) as it extends from just beneath the angle of the jaw to deep within the mediastinum.
C
D
FINAL DIAGNOSIS The final diagnosis was a cervical thymic cyst. DISCUSSION Embryologically, the thymus develops as sacculations from the ventrolateral aspect of the third pharyngeal pouch during the 6th week of life [1]. The dorsal wing of the same pouch gives rise to the inferior parathyroid glands. By the end of this week, the connection of the thymic primordia with the pharyngeal pouches is severed. Each primordium elongates caudally and medially as a tubular structure (thymopharyngeal tract), which soon begins a process of obliteration. By the 8th week
of life, the bilateral thymic primordia fuse in the midline and start to slide down under the sternum in the superior mediastinum. Speer [2] suggested five mechanisms for the pathogenesis of cyst formation within the thymus: embryologic remnants in the neck, sequestration products, neoplastic process, degeneration of Hassall's bodies, or mesenchymal elements. Fahmy [3] attributed the development of thymic cysts to the presence of sequestrated remnants within and adjacent to the gland across the line of descent. The site of the classic branchial cyst along the line of the thymopharyngeal tract, and the similarity of its epithelial lining to that of the thymic cyst, supports the idea that they are both derived from 1027
GEORGY
E T AL.
FIGURE 4. Intraoperative photograph shows the mass being pulled from the mediastinum through the thoracic inlet.
FIGURE 5. Light micrograph of the cyst wall with thymic tissue (T). A segment of lining composed of squamous cells is indicated (arrow). (Hematoxylin and eosin staining, original magnification, x16)
Vol. 2, No. 11, November 1995
cervical triangle [4] either anterior t o or deep to the sternomastoid muscle [5]. The fact that cervical thymic cysts are usually found within the carotid sheath may permit differentiation from large cysts of other origins [6]. Fewer than 100 cases of cervical thymic cysts have been reported in the literature. The cysts occur more frequently in males than females and in the left rather than right side of the neck [3, 5, 7]. Approximately 50% of the reported cases are connected to the mediastinum with a fibrous band [3]. The majority are multicystic [51. Cyst fluid may be clear, yellow, brown, green, or even purulent. Free-cholesterol crystals may be found in the fluid or embedded in the wall [8]. Normal thymic tissue with Hassall's corpuscles are often found within the cyst wall [8]. The cyst lining may be columnar, cuboidal, or stratified squamous epithelium [4]. The prognosis is excellent after surgical removal of the cyst [1]. Malignant transformation has been reported in one case [9]. The differential diagnosis of lateral neck mass in a child includes cystic hygroma, lymphangioma, branchial cleft cyst, lymphadenopathy, thyroid pathology, or thyroglossal cyst. Other rare lesions include dermoid cyst, teratomas, cystic degeneration of thymoma, cervical myelomeningocele, external laryngeal diverticulum, or cervical echinococcal hydatid cyst. Only thymic cysts and branchial cysts occur within the carotid sheath. In summary, cervical thymic cysts are rare. They arise from the remnant of the thymopharyngeal tract in the anterior triangle during the first decade of life; the prognosis after surgery is excellent. They should be included in the differential diagnosis of cystic neck masses in the appropriate clinical setting, particularly if the cysts lie between the carotid artery and internal jugular vein within the carotid sheath. REFERENCES
the same vestigial structure. Both lesions represent a variant of the same developmental anomaly in different age groups [3]. Two thirds of the cases of thymic cyst present during the first decade of life, whereas branchial cysts are the most c o m m o n in the third decade, w h e n more than 60% occur; only 2% are found in the first decade of life. Typically, the anatomic location is in the path of descent of the thymopharyngeal tract in the neck and in the mediastinum. In the neck, it is usually observed along a line extending from the angle of the mandible to the manubrium sterni, particularly in or near the anterior
1028
1. Tovi F, Mares AJ. The aberrant cervical thymus: embryology, pathology and clinical implications. Am J Surgery 1987;136:631-637. 2. Speer FD. Thymic cyst. NY Med Coil Flowers Hosp Bull 1938; 1:142. 3. Fahmy S. Cervical thymic cysts: their pathogenesis and relationship to branchial cysts. J Laryngol Oto11974;88:47-60. 4. Rosai J, Levine GD. Tumors of the thymus. In: Atlas of tumor Pathology (2nd series). Washington, DC: Armed Forces Institute of Pathology, 1987:207-211.
5. Lyons 1-, Dickson JAS. Varied s. cervical thymic cyst. J Pediatr Surg 1969; 24:241-243. 6. Levine C. Cervical presentation of a large thymic cyst: CT appearance. J Comput Assist Tomogr 1968;12:656-657. 7. Guba AM, Adam AE, Jaques DA, Chambers RG. Cervical presentation of thymic cysts. Am J Surgery 1978;136:430-436. 8. Reiner M, Beck AR, Rybak B. Cervical thymic cyst in children. Am J Surgery 1980; 139:704-707. 9. Leong ASY, Brown JH. Malignant transformation in a thymic cyst. Am J Surg Patho11984;8:471-475.