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Clinical Problem Solving: Radiology
Apr 2012

Radiology Quiz Case 2: Diagnosis

Author Affiliations
 

SECTION EDITOR: EDWARD B. STELOW, MD

Arch Otolaryngol Head Neck Surg. 2012;138(4):425. doi:10.1001/archoto.2012.193b

Diagnosis: Retropharyngeal prevertebral lipoma

Lipomas are benign neoplasms that originate from mesenchymal tissue.1 Despite being common in adults, they are rare in the pediatric population.2 In all age groups, lipomas are most commonly subcutaneous and only rarely arise from deep mesenchymal tissues.3 The most frequent locations are the trunk and limbs, with only 13% arising in the head and neck.4,5 In the head and neck, the common sites for lipomas are the supraclavicular fossa and the lateral and posterior subcutaneous areas of the neck.6,7

Lipomas of the upper aerodigestive tract are rare, and retropharyngeal lipomas are extremely rare.4,5 Indeed, to our knowledge, only 30 cases of retropharyngeal lipoma have been described in the literature since the late 1800s, and, of these, only 3 were reported to cause obstructive sleep apnea (OSA).3 All 30 reported cases were in adults. There is a single pediatric case of an 11-year-old girl who also presented with severe OSA, similar to our patient.2

Because of the slow rate of growth of lipomas, patient presentation is frequently delayed until there is cosmetic disfigurement or functional impairment.5 In the retropharyngeal space, lipomas can be asymptomatic for years until they reach a substantial size. When a critical size is reached, the patient typically presents with airway symptoms, which can include snoring, OSA, dyspnea, or nasal obstruction, depending on the size and position of the lesion.3 When the obstruction is at the oropharyngeal level, as in our case, airway collapse during sleep (when pharyngeal muscle tone decreases) gives rise to OSA.3

Macroscopically, lipomas appear as well-circumcised encapsulated tumors, and, microscopically, they consist of lobulated mature adipose tissue with intervening fibrous septae and no cellular atypia.1,8 Despite being histologically benign, a retropharyngeal lipoma is associated with mortality and morbidity secondary to airway obstruction.9

Imaging of retropharyngeal lipomas is a vital part of preoperative planning. It allows diagnosis and delineates the anatomy and relationship to vital structures (eg, the carotid sheath), which are best visualized on axial images. The craniocaudal extent of the tumor is best assessed on sagittal images. Because of better soft-tissue resolution and lack of ionizing radiation, the ideal modality is magnetic resonance imaging, but computed tomography may also be useful.8 On magnetic resonance images, lipomas exhibit high T1- and T2-weighted signal intensity. When fat suppression is used, there is signal dropout, similar to the subcutaneous fat. On computed tomograms, lipomas are homogeneous, well-circumcised, low-attenuated (−50 to −150 Hounsfield units) masses with thin fibrous septations that exhibit no contrast enhancement.2

Nonetheless, imaging cannot definitively exclude a low-grade liposarcoma, and surgical excision is usually recommended.1 Fine-needle aspiration cytology is not usually indicated as it does not definitively exclude liposarcoma and carries the risk of airway obstruction if hemorrhage ensues.1 The differential diagnosis of lipoma includes fibrolipoma and angiolipoma, depending on the connective tissue component and vascularity, respectively, and, in the pediatric population, lipoblastoma.1 Another variant of lipoma is the infiltrating or intramuscular type that has an incomplete capsule and infiltrates neighboring skeletal muscle and tissues. Recurrence rate for this variant is higher after surgical excision.10

In this case, the retropharyngeal lipoma was removed transorally without the need to perform a tracheostomy, mandibular split, or glossotomy. The potential surgical routes to the retropharyngeal space include transoral, lateral cervicotomy, or endoscopic approaches and depend on the site and size of the tumor as well as on its relationship to other structures (eg, vessels and nerves).9

Our patient was kept intubated for the first postoperative night and extubated the following morning. He quickly resumed a normal diet and was discharged on postoperative day 3. Not only did his OSA resolve, but also his rate of growth improved and his parents reported resolution of his daytime somnolence.

The patient will be followed up in 6 months. Follow-up for retropharyngeal lipoma is essential to look for recurrence, particularly in cases of nonradical extirpation. Moreover, a metachronous lipoma may arise, or the tumor may prove to be malignant. This follow-up is of particular importance because well-differentiated liposarcomas may be misdiagnosed as lipomas owing to their subtle histologic features.9

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References
1.
Hockstein NG, Anderson TA, Moonis G, Gustafson KS, Mirza N. Retropharyngeal lipoma causing obstructive sleep apnea: case report including five-year follow-up.  Laryngoscope. 2002;112(9):1603-160512352671PubMedGoogle ScholarCrossref
2.
Gong W, Wang E, Zhang B, Da J. A retropharyngeal lipoma causing obstructive sleep apnea in a child.  J Clin Sleep Med. 2006;2(3):328-32917561547PubMedGoogle Scholar
3.
Piccin O, Sorrenti G. Adult obstructive sleep apnea related to nasopharyngeal obstruction: a case of retropharyngeal lipoma and pathogenetic considerations.  Sleep Breath. 2007;11(4):305-30717676347PubMedGoogle ScholarCrossref
4.
Namyslowski G, Scierski W, Misiolek M, Urbaniec N, Lange D. Huge retropharyngeal lipoma causing obstructive sleep apnea: a case report.  Eur Arch Otorhinolaryngol. 2006;263(8):738-74016673079PubMedGoogle ScholarCrossref
5.
Persaud RA, Kotnis R, Ong CC, Bowdler DA. A rare case of a pedunculated lipoma in the pharynx.  Emerg Med J. 2002;19(3):27511971855PubMedGoogle ScholarCrossref
6.
Ahuja AT, King AD, Kew J, King W, Metreweli C. Head and neck lipomas: sonographic appearance.  AJNR Am J Neuroradiol. 1998;19(3):505-5089541308PubMedGoogle Scholar
7.
El-Monem MH, Gaafar AH, Magdy EA. Lipomas of the head and neck: presentation variability and diagnostic work-up.  J Laryngol Otol. 2006;120(1):47-5516359147PubMedGoogle ScholarCrossref
8.
Maran AG, Mackenzie IJ, Murray JA. The parapharyngeal space.  J Laryngol Otol. 1984;98(4):371-3806325567PubMedGoogle ScholarCrossref
9.
Tan KK, Abraham KA, Yeoh KH. Lipoma of hypopharynx.  Singapore Med J. 1994;35(2):219-2217939828PubMedGoogle Scholar
10.
Eloy JA, Carneiro E, Vibhute P, Genden EM, Bederson JB, Som PM. A rare prevertebral ordinary lipoma presenting as obstructive sleep apnea: computed tomographic and magnetic resonance imaging findings.  Arch Otolaryngol Head Neck Surg. 2008;134(9):1001-100318794447PubMedGoogle ScholarCrossref
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