Transverse sinus stenosis

Transverse sinus stenosis, or lateral sinus stenosis, describes reduction in the caliber of the transverse sinus. Although potentially seen in a number of contexts, including within the asymptomatic general population incidentally, transverse sinus stenosis is an important finding in patients with idiopathic intracranial hypertension.

Epidemiology

In the general population, one study utilizing CT angiography found that unilateral transverse sinus stenosis was present in almost 20% of cases, with stenosis occurring more commonly on the left side ¹. In the same study, bilateral transverse sinus stenosis was found in 5% of cases ¹, while a similar figure of 3% was found in another study utilizing MR venography ². In the general population, there is no gender predilection for having transverse sinus stenosis ¹.

Associations

In patients with idiopathic intracranial hypertension, transverse sinus stenosis is comparatively common, and is considered the most sensitive and specific sign ². One study utilizing MR venography found that bilateral transverse sinus stenosis was present in 93% of patients ².

Additionally, patients with a Chiari I malformation may also have a higher likelihood of transverse sinus stenosis ³. Patients with primary headache disorders, such as migraine or tension-type headache, may also have a higher likelihood of transverse sinus stenosis ⁷.

Clinical presentation

The clinical presentation may be highly variable. For example, patients with transverse sinus stenosis may be asymptomatic (as is the case when present in much of the general population), or may be symptomatic with pulsatile tinnitus or features of idiopathic intracranial hypertension (additional headache, visual changes, papilledema, etc.).

Pathology

Transverse sinus stenosis may be caused by intrinsic or extrinsic mechanisms ^4,5. In many patients, such as those with idiopathic intracranial hypertension, both mechanisms may be contributing concurrently ^4,5.

• intrinsic: stenosis caused by an intra-luminal structure ^4,5

  • arachnoid granulations

    • presence of arachnoid granulations is highly predictive of transverse sinus stenosis, seen in approximately 70% of patients with unilateral stenosis ¹

  • fibrous septae

  • organized chronic thrombus

  • congenital stenosis

• extrinsic: stenosis caused by external compression to the venous lumen ^4,5

  • raised intracranial pressure

    • the transverse sinuses collapse against the skull in the setting of raised intracranial pressure (e.g. in the setting of idiopathic intracranial hypertension)

    • this collapse leads to venous outflow obstruction, which decreases CSF absorption, leading to further increase in intracranial pressure

  • extradural (epidural) hematoma underlying an occipital bone fracture

  • local compressive brain parenchymal pathologies (e.g. tumors, herniations, etc.)

Radiographic features

CT and MRI

The transverse sinuses are best evaluated with dedicated venography, with non-invasive techniques such as CT venography or MR venography being most commonly utilized.

There is a lack of consensus among different studies regarding the radiographic definition for transverse sinus stenosis, with stenosis being variably defined as a >40-50% reduction in vessel caliber ^1,2. Interestingly, the degree of radiographic stenosis needed to correlate with a significant trans-stenosis pressure gradient may be lower than this, with one study finding that a significant degree of stenosis was 30-35%, with every 10% increase in stenosis correlating with an approximate increase of 3.5 mmHg in the trans-stenosis pressure gradient ⁹. In the setting of evaluation for idiopathic intracranial hypertension, the degree of stenosis can be used to calculate the 'index of transverse sinus stenosis' and 'combined venous conduit patency' scores, which may aid in diagnosis ^11,12.

When present, the morphology of the stenosis is variable depending on whether the stenosis is intrinsic or extrinsic in etiology ⁵. It should be noted that in idiopathic intracranial hypertension, which classically demonstrates bilateral transverse sinus stenoses, both intrinsic and extrinsic etiological mechanisms may be present, thus, the morphology of the stenoses may have features of either or both mechanisms ⁵.

• intrinsic: discrete filling defects within the transverse sinus resulting in stenosis

• extrinsic: smooth regions of collapsing or flattening or tapering of the transverse sinus resulting in stenosis, typically in the distal segment at the transverse-sigmoid sinus junction

  • this may not be apparent if a lumbar puncture has been performed recently, as a lumbar puncture can reverse extrinsic stenosis ¹⁰

Additionally, the high pressure jet of blood through the stenosis can result in post-stenotic dilatation with bony remodeling of the proximal sigmoid sinus, known as a sigmoid sinus diverticulum ⁸.

Digital subtraction venography

Although rarely used to assess morphology alone, transverse sinus stenosis can also be evaluated with invasive cerebral venography ⁵. This technique additionally allows for venous manometry to be performed, which is the gold standard for measuring the trans-stenosis pressure gradient ⁵. A gradient of >8 mmHg across the transverse sinus stenosis is generally considered abnormal ⁵, although individual institutional practice may vary.

Treatment and prognosis

If symptomatic and with an abnormal trans-stenotic pressure gradient, transverse venous stenosis can be managed with endovascular stent placement. For example, in a 2024 meta-analysis of patients with idiopathic intracranial hypertension, stenting of the transverse sinus improved headaches (~80%), papilledema (~90%), and visual disturbances (~90%) ⁶.

Complications

Complications of stent placement include ⁶:

• treatment failure or stenosis recurrence (often adjacent to stent)

• stent thrombosis (antiplatelet therapy is given to prevent this)

• subdural hemorrhage

• infection

Differential diagnosis

• transverse sinus hypoplasia: a hypoplastic sinus was defined in one study as being 40% smaller in average caliber than the contralateral sinus ¹, more commonly the right side is dominant

• transverse sinus thrombosis

Practical points

• transverse sinus stenosis may be due to intrinsic or extrinsic mechanisms, and in idiopathic intracranial hypertension often both mechanisms are in effect

• recent lumbar puncture can reverse transverse sinus stenosis

• the gold standard for assessing the degree of trans-stenosis pressure gradient is with invasive venous manometry, with a gradient of >8 mmHg generally considered abnormal

• transverse sinus stenosis may be amenable to endovascular stenting