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Endolymphatic Sac Tumour

Summary

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  • Rare, locally aggressive neoplasm arising from the endolymphatic sac of the inner ear
  • Characterised by slow growth, local invasion, and bone destruction
  • Imaging shows a destructive temporal bone mass with heterogeneous enhancement

Pathophysiology

  • Originates from the endolymphatic sac epithelium in the posterior petrous temporal bone
  • Typically sporadic, but can be associated with von Hippel-Lindau (VHL) syndrome
  • Slow-growing but locally invasive, causing bone erosion and destruction
  • May extend into the cerebellopontine angle and posterior cranial fossa

Demographics

  • Rare tumour, with fewer than 300 cases reported in literature
  • Affects all age groups, but most common in 30-40 year olds
  • No significant gender predilection
  • Higher incidence in patients with VHL syndrome (up to 16%)

Diagnosis

  • Clinical presentation:
    • Hearing loss (most common)
    • Tinnitus
    • Vertigo
    • Facial nerve palsy (in advanced cases)
  • Otoscopic examination may reveal a blue mass behind the tympanic membrane
  • Audiometry typically shows sensorineural hearing loss
  • Vestibular function tests may be abnormal

Imaging

  • CT findings:
    • Destructive, expansile mass in the posterior petrous temporal bone
    • Heterogeneous density with areas of calcification
    • "Moth-eaten" appearance of bone erosion
  • MRI findings:
    • T1: heterogeneous signal intensity
    • T2: heterogeneous, often hyperintense
    • T1 post-contrast: avid, heterogeneous enhancement
    • "Salt and pepper" appearance due to flow voids and haemorrhage
  • Angiography:
    • Hypervascular mass with feeding vessels from external carotid artery branches
    • May show early venous drainage

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  • 45-year-old patient presented with sensorineural hearing loss, tinnitus and dizziness for 2 months.
  • MRI showed enhancement within the vesitubular aqueduct, vestibule and proximal semicircular canals.
  • CT showed widening of the vestibular aqueduct with a moth-eaten margin (red arrows).

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  • 30-year-old patient with a prior left cerebellar hemangioblastoma developed a lesion in the right petrous bone.
  • The lesion centred in the right vestibular aqueduct, which was T2-hyperintense and enhanced after gadolinium, was compatible with an endolymphatic sac tumour.
  • The patient was diagnosed with von Hippel Lindau.

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  • A 20-year-old patient presented with a worsening left facial nerve palsy.
  • CT showed an expansile left petrous bone lesion eroding the facial canal (and lateral semicircular canal).
  • MRI showed a T1- and T2-hyperintense lesions with central enhancement without diffusion restriction.
  • Following resection, an ELST was diagnosed. There were no other retinal or abdominal manifestations of vHL.

Treatment

  • Surgery is the primary treatment modality
    • Complete resection is the goal, but may be challenging due to location
    • Preoperative embolization may reduce intraoperative bleeding
  • Stereotactic radiosurgery:
    • Alternative for small tumours or residual disease
    • May be used in combination with surgery
  • Chemotherapy:
    • Limited role in primary treatment
    • May be considered for metastatic disease (rare)
  • Follow-up:
    • Long-term imaging surveillance is necessary due to risk of recurrence
    • Annual screening recommended for patients with VHL syndrome

Differential diagnosis

Differential Diagnosis Differentiating Feature
Vestibular schwannoma Typically centered on internal auditory canal; Endolymphatic sac tumour (ELST) is centered on posterior petrous bone
Paraganglioma Characteristic "salt and pepper" appearance on MRI; ELST is more homogeneous
Meningioma Dural tail sign often present; ELST lacks this feature
Cholesterol granuloma Hyperintense on T1-weighted MRI; ELST is usually isointense
Metastasis Multiple lesions often present; ELST is typically solitary
Cholesteatoma Restricted diffusion on DWI; ELST does not typically show restricted diffusion
Facial nerve schwannoma Follows the course of facial nerve; ELST is centered on endolymphatic sac
Petrous apex lesion Located more anteriorly in petrous bone; ELST is posterolateral
Aneurysm Flow voids on MRI; ELST shows solid enhancement
Arachnoid cyst No enhancement; ELST typically enhances on contrast-enhanced imaging