Endolymphatic sac tumour

Endolymphatic sac tumours are very rare, locally invasive tumours of endolymphatic sac. Early detection of these tumours is critical, because early surgical intervention may prevent further hearing loss. Endolymphatic sac tumours do not metastasise but are highly locally aggressive. 

Epidemiology

Typically endolymphatic sac tumours are encountered in young individuals, with a mean age at onset of 22 years ².

Associations

Endolymphatic tumours are most often associated with von Hippel-Lindau disease and are detected in 11-16% patients with von Hippel-Lindau disease ². However, in ~60% of patients with von Hippel-Lindau disease and vestibulocochlear symptoms, there is no evidence on imaging of an endolymphatic sac tumour ².  

When these tumours are present in the setting of von Hippel-Lindau disease, then 30% of tumours are bilateral ².

Clinical presentation

Endolymphatic sac tumours typically present with the following symptoms and signs:

• hearing loss: 95%

  • acute (43%)

  • gradual (remainder)

• tinnitus: 92%

• vertigo or disequilibrium: 62%

• aural fullness: 29%

• facial paresis: 8%

Pathology

These tumours are composed of two histological types:

• mixed type: generally confined

• papillary adenomatous type: more aggressive and often locally invades the temporal bone

Radiographic features

Generally, endolymphatic sac tumours always arise within the vestibular aqueduct, involving the endolymphatic sac or duct. Therefore, the lesion is centred in the posterior (retrolabyrinthine) petrous bone.

CT

• erosion of petrous bone in an infiltrative or "moth-eaten" pattern

• central calcific spiculation and posterior rim calcification ⁵

• often intense enhancement

MRI

Signal characteristics include ⁵

• T1: most show foci of hyperintensity

• T1 C+ (Gd): heterogeneous enhancement, involving the non-cystic component of the tumour

• T2: heterogeneous signal

Treatment and prognosis

Surgical excision is the treatment of choice when possible ³.

History and etymology

It was first described in 1989 by Dennis K Heffner, an American physician ⁴. Earlier than this they were probably misdiagnosed as choroid plexus tumours, adenomas, and adenocarcinomas of posterior fossa or cerebellopontine angle. 

Differential diagnosis

Possible imaging differential considerations include:

• jugular paraganglioma

  • centre of the lesion will be at the jugular bulb rather than the vestibular aqueduct

• enlarged vestibular aqueduct

  • expansion of aqueduct, with smooth margins

  • normal shape of the aqueduct maintained

• petrous apicitis

  • located in the petrous air cells

  • bone around the aqueduct is not usually aerated

• cholesterol granuloma

  • most often located in the petrous apex, not vestibular aqueduct

• meningioma

  • hyperostotic underlying bone

• bony metastasis