====== Brain biopsy for Herpes simplex encephalitis ======

[[Indication]]s for [[brain biopsy]]: reserved for questionable cases. May not be necessary for patients with [[fever]], [[encephalopathy]], compatible CSF findings, focal neuro findings ([[focal seizure]], [[hemiparesis]], or [[cranial nerve palsy]]), and supporting evidence of at least one of the following: focal EEG, CT, MRI or technetium brain scan abnormality.

Should be performed within ≤48 hrs of starting [[acyclovir]] (otherwise false negatives may occur).

Biopsy results: of 432 brain biopsies performed using the technique below, 45% had HSE, 22% had identifiable but non-HSE pathology (e.g. vascular disease, other viral infection, adrenal leukodystrophy, bacterial infection...), and 33% remained without a diagnosis
((Whitley RJ, Cobbs CG, Alford CA, et al. Diseases that Mimic Herpes Simplex Encephalitis: Diagnosis, Presentation, and Outcome. JAMA. 1989; 262:234–239)).

==== Technique ====

1. anterior inferior [[temporal lobe]] is preferred site

a) the side chosen for a biopsy is the one showing maximal involvement based on clinical information (e.g. localizing seizures), EEG and/or imaging studies
((Schlitt MJ, Morawetz RB, Bonnin JM, Zeiger HE, Whitley RJ. Brain Biopsy for Encephalitis. Clin Neurosurg. 1986; 33:591–602)).

b) 10 ×10 ×5 mm deep specimen obtained from the anterior portion of the [[inferior temporal gyrus]] with NO COAGULATION on specimen side (cut surface with #11 blade, then cauterize pial surface on the non-specimen side)

c) 2nd specimen obtained from beneath surface specimen with fenestrated pituitary biopsy forceps

2. virus isolation is the most specific (100%) and sensitive (96–97%) test for HSE. Other findings (less accurate): perivascular cuffing, lymphocytic infiltration, hemorrhagic necrosis, neuronophagia, intranuclear inclusions (present in 50%)

3. if electron microscopy (EM) or immunohistofluorescence is available, 70% may be diagnosed within ≈ 3 hrs of biopsy

4. biopsy tissue handling

a) avoid macerating specimens for histology

b) tissue for EM: placed in glutaraldehyde

c) tissue for permanent histology: placed in formalin

d) tissue for culture:

● handling: the specimen is placed in a sterile specimen container and sent directly to the virology lab. If lab is closed, tissue may be placed in a regular refrigerator for up to 24 hrs or placed in – 70°C freezer for an indefinite time (virus remains viable for up to 5 yrs). DO NOT place the specimen in a regular freezer (destroys virus)

● cultures generally take at least 1 week to become positive

● cultures checked for 3 weeks before being declared negative