Sluggish Flow in Left Transverse and Sigmoid Sinuses - MRI Interpretation

What This Finding Means

Anatomy Review

"Often, one hypoplastic transverse sinus can cause confusion if a sinus thrombosis is suspected. In these cases, the jugular notch in the occipital bone and jugular foramen may be smaller on the side of the hypoplastic transverse sinus."

• Goldman-Cecil Medicine

Why Slow Flow Can Mimic Thrombosis on MRI

• Normal venous sinuses appear as bright/hyperintense flow signal
• Absent or reduced flow = loss of that signal, which looks like thrombosis
• But: slow/sluggish flow also causes loss of the TOF signal, creating a "flow gap" artifact

"Variations in the speed of blood flow and anatomical variants of the venous sinuses may change their usual signal characteristics, leading to a false diagnosis of venous sinus thrombosis. Slow flow in a venous sinus may cause increased signal on T1- and T2-weighted images, potentially leading to a false assumption of thrombosis."

• Bradley & Daroff's Neurology in Clinical Practice

How to Differentiate: What to Look For

• In true thrombosis: loss of normal T1/T2 flow void + signal intensity changes in the sinus itself (iso- then hyperintense as clot ages, especially on T1 when methemoglobin forms)
• In slow flow/hypoplasia: T1 and T2 images usually show no thrombus signal within the sinus lumen

• Absent or severely reduced flow signal in the affected sinus
• In thrombosis: often accompanied by engorged cortical draining veins "upstream"
• In hypoplasia: contralateral sinus is dominant, ipsilateral jugular foramen/notch may be smaller

• Slow flow / hypoplasia: gadolinium fills the sinus, confirming patency
• True thrombosis: "empty delta sign" / no contrast filling within the lumen; only peripheral/dural wall enhancement around the clot
• Phase-contrast MRV can also detect very slow flow that TOF misses

• Thrombosed sinuses appear expanded and exaggeratedly hypointense ("blooming")
• Prominent serpiginous veins in the drainage territory indicate venous congestion

MRI showing lateral (transverse) sinus thrombosis - Goldman-Cecil Medicine

Red Flags for True CVST

• Headache (especially new, progressive, or thunderclap)
• Papilledema / raised ICP symptoms (visual changes, pulsatile tinnitus)
• Seizures, focal neurological deficits, or encephalopathy
• Left temporal/parietal parenchymal abnormality on the same MRI (edema, FLAIR signal, hemorrhagic venous infarct - characteristically in the posterolateral temporal lobe / inferior parietal lobule for lateral sinus involvement)
• Risk factors: oral contraceptive use, pregnancy/puerperium, thrombophilia, dehydration, mastoiditis/otitis media (septic lateral sinus thrombosis), malignancy, Behcet disease

Causes of True Left Transverse/Sigmoid Sinus Thrombosis

Recommended Workup

1. Gadolinium-enhanced MRI/MRV - most important next step; demonstrates whether contrast fills the sinus (rules out thrombosis) or shows empty delta sign (confirms thrombosis)
2. CT venography (CTV) - excellent alternative; optimal for major dural sinus thrombosis; shows the delta sign (intraluminal clot surrounded by contrast)
3. SWI sequence - if not already done; very sensitive for sinus thrombosis
4. Compare sinus size bilaterally - if left transverse is hypoplastic by anatomy (smaller jugular foramen, nondominant side), this likely represents a benign variant
5. If CVST confirmed: thrombophilia screen, mastoid assessment, coagulation studies

Clinical Bottom Line

Final Diagnosis: Cerebral Venous Sinus Thrombosis (CVST) - Left Lateral Sinus

The Diagnostic Triad Is Complete

"CVT should be suspected in patients presenting with stroke symptoms without risk factors, unexplained new seizures or refractory headaches, or signs of intracranial hypertension."

• Rosen's Emergency Medicine

Why This Is No Longer a Diagnostic Dilemma

• A hypoplastic sinus does not cause hemorrhagic infarction - it is a structural absence with no outflow obstruction
• A slow flow artifact does not cause parenchymal injury
• Only true thrombosis with venous hypertension causes the downstream parenchymal damage seen here

"If anticoagulation is not implemented early, the reduction in parenchymal venous drainage leads to venous hypertension and subsequent infarction, which is frequently haemorrhagic."

• Grainger & Allison's Diagnostic Radiology

Pathophysiology

Thrombus in left transverse + sigmoid sinus
        ↓
Obstruction of venous outflow
        ↓
Venous hypertension in left posterolateral hemisphere
        ↓
Interstitial edema (vasogenic, then cytotoxic)
        ↓
Hemorrhagic venous infarct (left temporal/parietal cortex)
        ↓
Cortical irritation → Seizures

Next Steps

1. Gadolinium-enhanced MRI + MRV - still needed to confirm extent and rule out additional sinus involvement (superior sagittal sinus, straight sinus)
2. CT venography - excellent alternative; shows the "empty delta sign" (intraluminal clot surrounded by contrast) and defines extent
3. SWI sequence - shows "blooming" in the thrombosed sinus and identifies all hemorrhagic foci
4. Urgent anticoagulation - LMWH preferred over UFH; even in the presence of hemorrhagic infarction, anticoagulation is still indicated (evidence shows it does not worsen hemorrhage and prevents clot propagation)
5. Seizure management - antiepileptic drug (e.g., levetiracetam)
6. Thrombophilia workup - antiphospholipid antibodies, protein C/S, factor V Leiden, prothrombin gene mutation
7. Look for precipitant - oral contraceptive use? mastoiditis (check mastoid signal on the same MRI)? pregnancy/puerperium? malignancy?

Summary

Final Diagnosis: Left-sided Cerebral Venous Sinus Thrombosis (CVST) involving the left transverse and sigmoid sinuses, complicated by hemorrhagic venous infarction and seizures.