Q) What do we know about Sigmoid Sinus Wall Anomalies (SSWA) and Pulsatile Tinnitus (PST)?
Sigmoid Sinus Wall Anomalies (SSWA) - The sigmoid sinus is a blood-carrying channel on the side of the brain that receives blood from veins within the brain. SSWA refers to sinus wall abnormalities that cause pressure, blood flow and noise changes within the sigmoid sinus, causing PST. They include:
Sigmoid Sinus Diverticulum - the formation of diverticula or small pouches that extend through the sigmoid sinus wall into the mastoid bone behind the ear.; and
Sigmoid Sinus Dehiscence - refers to a missing part of the bone that surrounds the sigmoid sinus in the mastoid.
SSWA accounts for 20% of all causes of PST and is the most common venous PST. SSWA are treatable conditions but these conditions might be easily overlooked. The spectrum of SSWA includes a thin but intact sigmoid sinus plate, focal dehiscence of the sigmoid sinus plate, diverticulum, and ectasia with smooth bulging of the sigmoid sinus into the mastoid air cells without a focal diverticulum. More than one anomaly can coexist. The location of SSWA is immediately distal to the transverse-sigmoid junction.
Most patients with SSWA are female, with mean age of about 36.6 years old (25-40), have high BMI (body mass index), and have high opening CSF pressure from lumbar puncture. The prevalence of SSWA in patients with PST was 23% versus 1.2% in asymptomatic patients.
What are the associated conditions?
Most patients with SSWA were found to have bilateral Transverse Sinus Stenosis (TSS) to some degree and patients with sigmoid sinus diverticulum were more likely to have distal ipsilateral TSS than patients with sigmoid sinus dehiscence. Previous studies showed a strong association between SSWA and idiopathic intracranial hypertension (IIH) and high incidence of TSS in patients with IIHT. Hewes et al suggested that all patients with SSWA should be evaluated for IIH and that lumbar puncture should only be performed for patients who meet standard clinical practice indication.
What is the pathophysiology?
Eisenman proposed pathophysiologic development of SSWA where the TSS (ipsilateral or contralateral) causes elevated flow velocity and volume. This leads to progressive erosion of the bony sinus wall which eventually causes dehiscence and the formation of diverticulum. (Fig 1). However, this explanation doesn’t explain the situation of SSWA without TSS.
How do we explain the sound coming from SSWA? Eisenman described that once SSWA are formed, the sound can be from vibration of the dehiscence +/- thinned sinus wall or turbulence in a diverticulum. He also further explained that there are several factors involved in creating the sounds such as degree and length of TSS, size of dehiscence, and viscosity etc.
What is the study of choice for SSWA diagnosis?
The study of choice for SSWA diagnosis is CT angiogram timed to visualize both arterial and venous structure with temporal bone reconstruction. Ettreddy et al emphasized the importance of the entire vasculature system including the carotid, jugular bulb and transverse sinuses when evaluating PST patients.
What are treatment options?
Endovascular treatment for diverticulum using coil +/- stent to prevent coil migration.
Surgical treatment by transmastoid sigmoid sinus wall reconstruction for diverticulum or dehiscence. Please see Eisenman’s papers for more detail of the operation. Eisenman et al reported 90% of patients (36/40) had complete resolution of PST after surgery including all patients with diverticulum. However, patients with sigmoid sinus dehiscence without diverticulum without TSS or empty sella are less likely to respond to surgery. Ettyreddy et al reported complete resolution of PST in 84.2 % (16/19) after surgery for patients with suspected sigmoid sinus dehiscence.
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Mattox DE, Hudgins P. Algorithm for evaluation of pulsatile tinnitus. Acta Otolaryngol. 2008 Apr;128(4):427-31.
Reardon MA, Raghavan P. Venous Abnormalities Leading to Tinnitus: Imaging Evaluation. Neuroimaging Clin N Am. 2016 May;26(2):237-45
Hewes D, Morales R, Raghavan P, Eisenman DJ. Pattern and severity of transverse sinus stenosis in patients with pulsatile tinnitus associated with sigmoid sinus wall anomalies. Laryngoscope. 2020 Apr;130(4):1028-1033.
Eisenman DJ, Raghavan P, Hertzano R, Morales R. Evaluation and treatment of pulsatile tinnitus associated with sigmoid sinus wall anomalies. Laryngoscope. 2018 Oct;128 Suppl 2:S1-S13.
Ettyreddy AR, Shew MA, Durakovic N, Chole RA, Herzog J, Buchman CA, Wick CC. Prevalence, Surgical Management, and Audiologic Impact of Sigmoid Sinus Dehiscence Causing Pulsatile Tinnitus. Otol Neurotol. 2021 Jan;42(1):82-91.
Eisenman DJ. Sinus wall reconstruction for sigmoid sinus diverticulum and dehiscence: a standardized surgical procedure for a range of radiographic findings. Otol Neurotol. 2011 Sep;32(7):1116-9.