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Sigmoid Sinus Dehiscence

Summary

  • Sigmoid sinus dehiscence is characterised by absence of bone overlying the sigmoid sinus
  • Presents with pulsatile tinnitus and may be associated with intracranial hypotension
  • Diagnosis relies on high-resolution CT imaging of the temporal bone

Pathophysiology

  • Thinning or absence of bone between sigmoid sinus and mastoid air cells
  • May be congenital or acquired (e.g. due to increased intracranial pressure)
  • Leads to transmission of venous pulsations to surrounding structures

Demographics

  • More common in females (female:male ratio approximately 2:1)
  • Typically presents in middle-aged adults (40-60 years)
  • Prevalence estimated at 1.2% in asymptomatic population

Diagnosis

  • Clinical presentation:
    • Pulsatile tinnitus (most common symptom)
    • Hearing loss
    • Vertigo
    • Headache
  • Otoscopic examination may reveal a bluish mass behind the tympanic membrane
  • Valsalva manoeuvre may alter the intensity of tinnitus

Imaging

  • High-resolution CT of the temporal bone:
    • Gold standard for diagnosis
    • Absence of bone overlying sigmoid sinus
    • Thinning of surrounding bone
    • Possible protrusion of sinus into mastoid air cells
  • MRI:
    • T2-weighted images may show flow voids
    • MR venography can assess sinus patency and flow
  • Digital subtraction angiography:
    • Not routinely used but may be helpful in complex cases

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  • A 30-year-old female presented with low frequency pulsatile tinnitus that ceased following palpation of the left jugular vein.
  • CT showed a focal region of absence of bone over a mastoid air cell, consistent with sigmoid plate dehisence.

Treatment

  • Conservative management:
    • Reassurance and education
    • Sound therapy for tinnitus management
  • Surgical options:
    • Transmastoid sigmoid sinus wall reconstruction
    • Endovascular coil embolisation in selected cases
  • Treatment of underlying causes (e.g. intracranial hypertension) if identified

Differential diagnosis

Differential Diagnosis Distinguishing Feature
Glomus tympanicum Enhancing mass on CT/MRI, "salt and pepper" appearance on T2-weighted MRI
Cholesteatoma Expansile soft tissue mass with bone erosion, non-enhancing on MRI
High jugular bulb Located more inferiorly, smooth margins, no associated symptoms
Aberrant internal carotid artery Anterior location in middle ear on CT; aberrant course lateral to the cochlea
Otosclerosis Lucent halo around cochlea on CT; fissula ante fenestram involvement; no vascular defect
Semicircular canal dehiscence Bony defect involves the superior semicircular canal rather than the sigmoid sinus plate
Petrous apex cholesterol granuloma Expansile lesion in petrous apex, hyperintense on T1-weighted MRI
Paraganglioma Enhancing mass, "salt and pepper" appearance on MRI, may involve jugular foramen