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SECTION EDITOR: EDWARD B. STELOW, MD
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
Return to Quiz Case.
Radiology Quiz Case 2: Diagnosis. Arch Otolaryngol Head Neck Surg. 2012;138(4):425. doi:10.1001/archoto.2012.193b
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