Management of Temporal Lobe Lesions

Initial Diagnostic Approach

The American College of Radiology recommends MRI with specific epilepsy protocols to characterize the lesion and determine the etiology, which may include herpes simplex encephalitis, mesial temporal sclerosis, or low-grade epilepsy-associated tumors 1, 2
Bilateral temporal lobe involvement with low-density lesions is nearly pathognomonic for herpes simplex encephalitis, which requires immediate empiric acyclovir treatment 1, 3
MRI reveals temporal and/or inferior frontal lobe edema with high signal intensity on FLAIR and T2-weighted images, with more than 90% of HSE cases documented by CSF PCR showing MRI abnormalities 1
CSF PCR for HSV-1 and HSV-2 has 95% sensitivity and 99% specificity and should be obtained immediately if HSE is suspected, with a strength of evidence rated as high 3

Mesial temporal sclerosis is the most common cause of temporal lobe seizures and presents as hippocampal atrophy with increased T2/FLAIR signal, with MRI showing sensitivity of 84% for MTS 4, 2
Dysembryoplastic neuroepithelial tumors are indolent tumors with benign pathology that remain clinically stable over many years, typically presenting in children and young adults with long-standing, medically intractable epilepsy 5, 6

The Infectious Diseases Society of America recommends initiating acyclovir immediately without waiting for confirmatory testing if clinical suspicion of herpes simplex encephalitis is high, with a strength of evidence rated as moderate (B-III recommendation) 3
Complete surgical resection of the epileptogenic region via temporal lobectomy is the treatment of choice for medically refractory mesial temporal sclerosis, with extended resection showing higher success rates and low morbidity compared to lesionectomy alone 7, 2
Complete excision of the DNET together with a rim of surrounding dysplastic brain is the most efficient surgical approach for low-grade epilepsy-associated tumors, given higher success rates and low morbidity 7

FDG-PET should be obtained when MRI is normal or shows nonspecific findings, with sensitivity of 63-67% for detecting metabolic abnormalities in temporal lobe epilepsy, and is recommended by the American College of Radiology 2
Concordance between multiple diagnostic modalities (MRI, EEG, PET, SPECT) is associated with better surgical outcomes, with a strength of evidence rated as high 2

Never delay empiric acyclovir if herpes simplex encephalitis is in the differential, as bilateral temporal involvement is nearly pathognomonic and mortality is high without treatment, with a strength of evidence rated as high 1, 3
Incomplete surgical resection dramatically increases seizure recurrence rates, and complete removal of both the lesion and surrounding dysplastic cortex is essential, with a strength of evidence rated as moderate 5, 7, 2