What does enhancement of the left medial temporal lobe on a brain MRI indicate?

Enhancement of Left Medial Temporal Lobe on Brain MRI: Diagnostic Implications

Enhancement of the left medial temporal lobe on brain MRI most commonly suggests an active pathological process involving blood-brain barrier disruption and should prompt urgent evaluation for cerebral venous thrombosis, inflammatory conditions, or neoplastic processes.

Common Causes of Medial Temporal Lobe Enhancement

Vascular Causes

• Cerebral venous thrombosis (CVT), particularly involving cortical veins in the temporal region, can present with enhancement of the medial temporal lobe due to venous congestion and blood-brain barrier disruption 1
• Isolated cortical vein thrombosis (ICVT) may present with ipsilateral dural enhancement and thickening in the affected region 1
• Developmental venous anomalies or capillary telangiectasias can show enhancement patterns that might be confused with pathological enhancement 1

Inflammatory/Demyelinating Causes

• Amyloid-related imaging abnormalities (ARIA) can present with enhancement in various brain regions, including the temporal lobes 1
• Multiple sclerosis lesions may show nodular or ring enhancement, though typically these are not limited to the medial temporal lobe 1
• Mesial temporal sclerosis, while primarily characterized by atrophy, may occasionally show enhancement during active inflammation 2

Neoplastic Causes

• Tumors (primary or metastatic) can present with enhancement in the medial temporal lobe 1
• Tumefactive demyelinating lesions can mimic neoplasms with their enhancement patterns 1

Diagnostic Approach

Imaging Characteristics to Evaluate

• Pattern of enhancement: nodular, ring-like, or "open-ring" (open toward ventricles or cortex) 1
• Associated findings: check for T2/FLAIR hyperintensity, diffusion restriction, or susceptibility effects suggesting hemorrhage 1
• Presence of mass effect or surrounding edema 1
• Vascular abnormalities: absence of flow void in venous structures, altered signal intensity in dural sinuses 1

Additional Imaging Recommended

• Contrast-enhanced MRI with MR venography (MRV) should be performed to evaluate for cerebral venous thrombosis 1
• Consider CT venography (CTV) as an alternative if MRV is not available 1
• Diffusion-weighted imaging (DWI) to assess for restricted diffusion, which may help differentiate between vascular and non-vascular causes 1
• Susceptibility-weighted imaging (SWI) to detect microhemorrhages or venous abnormalities 1

Clinical Correlation

Cerebral Venous Thrombosis

• If enhancement is associated with absence of flow void in venous structures, consider cerebral venous thrombosis 1
• Brain parenchymal changes in the temporal lobe often correspond to lateral (transverse) and sigmoid sinus thrombosis 1
• Urgent anticoagulation therapy may be indicated to prevent intracranial hemorrhage and improve outcomes 1

Alzheimer's Disease and Other Dementias

• While medial temporal lobe atrophy is a characteristic finding in Alzheimer's disease, enhancement is not typically seen 3
• Enhancement in the setting of known or suspected dementia should raise concern for an alternative or additional pathology 1
• Functional abnormalities of the medial temporal lobe memory system are common in mild cognitive impairment and Alzheimer's disease, but these do not typically manifest as enhancement 4

Important Pitfalls to Avoid

• Do not mistake normal vascular structures for pathological enhancement - always confirm enhancement corresponds to an abnormality on T2/FLAIR sequences 1
• Enhancement persisting longer than 3 months should raise suspicion for alternative pathologies such as sarcoidosis or vascular abnormalities 1
• Avoid misinterpreting flow artifacts from nearby vessels as true enhancement - pre-contrast T1-weighted images can help differentiate 1
• Do not overlook the possibility of leptomeningeal enhancement, which is rare in multiple sclerosis but may indicate other inflammatory conditions 1

When to Consider Urgent Intervention

• Enhancement associated with clinical symptoms such as headache, seizures, or focal neurological deficits requires immediate evaluation 1
• If cerebral venous thrombosis is suspected, urgent neuroimaging with venography and consideration of anticoagulation is warranted 1
• In cases where enhancement is associated with mass effect and clinical deterioration, neurosurgical consultation may be necessary 1