DIAGNOSIS: Cystic and papillary neoplasm of endolymphatic sac origin (Heffner tumor).
DISCUSSANT: Mahmood F. Mafee, MD
The membranous labyrinth or cavity consists of the cochlear aqueduct, the vestibular organ, the endolymphatic duct and sac, the round window membrane, and their associated vasculature. The bony labyrinth includes the vestibule, the semicircular canals, and the cochlea. The membranous labyrinth of the inner ear begins to form during the early months of gestation. By mid-term, the mesenchyme that surrounds the labyrinth has transformed into cartilage, and begins to ossify. The endolymphatic duct and sac are the only portions that grow after birth, and they continue to enlarge until sometime after puberty.
There is considerable controversy concerning the origin of these slowly growing, yet highly destructive lesions of the temporal bone. Several recent reports have emphasized that these tumors probably do arise from the epithelial elements lining the endolymphatic system (especially the sac). The most common presentation is hearing loss, facial nerve palsy, and vestibular dysfunction.
There appear to be at least 2 categories of this lesion, a slowly growing, relatively benign adenomatous tumor, and a more aggressive lesion with a capillary configuration. The papillary lesions probably arise within the posterior aspects of the petrous bone in the retrolabyrinthine region. The lesions may be hypervascular, supplied by branches of the external carotid artery, and may contain blood products that produce characteristic regions of hyperintensity on T1WI and hypointensity on T2WI. Intratumoral calcifications within these lesions may represent "bone sequestra" produced when the tumor infiltrates into the petrous bone. Because these lesions may be surrounded by a thin shell of reactive bone, it has been suggested that at least during some portion of their growth, they may expand relatively slowly. The lesions almost invariably show contrast enhancement. Some of the tumors have a speckled pattern of hyperintensity on T1WI, which can mimic the appearance of other vascular lesions of the petrous apex, including glomus tumors.
The papillary endolymphatic sac tumor has been associated with von Hippel-Lindau disease (VHL)and may present with bilateral papillary endolymphatic sac neoplasms. It is also interesting to remember that patients with VHL may develop cystadenomas in the testis and in relationship to the female pelvic adnexa.
In this patient, the differential diagnosis could include chondroid lesions (benign chondroma as well as low-grade chondrosarcoma, and chondromyxoid fibroma), cholesterol granuloma, metastatic disease, and possibly an aggressive epidermoid cyst.
Because the histology of this lesion may be confusing to surgical pathologists, an accurate preoperative localization by neuroimaging can assist in suggesting the correct diagnosis. The prognosis can be quite good after careful gross removal of the lesion. However, incomplete resection is associated with recurrence.
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