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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 bone1

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

panels-1

  • 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 dehiscence.

Treatment

  • Reassurance, or transmastoid sinus wall resurfacing for disabling pulsatile tinnitus. Look for associated signs of idiopathic intracranial hypertension

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

  1. Sotoudeh et al. Prevalence of Sigmoid Sinus Dehiscence and Diverticulum among Adults with Skull Base Cephaloceles. 2020. AJNR. American journal of neuroradiology - Open in new tab. ↩