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DWI Is Important Test in Neonatal HSV-2 Encephalitis

August 7, 2009
Written by: , Filed in: Neuroradiology, Pediatric Radiology
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Neonatal herpes simplex virus type 2 (HSV-2) encephalitis is a very serious disease that requires early recognition and treatment. It is most commonly acquired during delivery and presents in the second to fourth week of life.

The objective of a recent study was to determine the CT, MRI, and diffusion-weighted imaging (DWI) findings in neonatal HSV-2 encephalitis.

The retrospective review studied 12 patients presenting with neonatal HSV-2 encephalitis between 1994 and 2002.

Based upon the results, it would appear that diffusion-weighted imaging is the most sensitive modality for demonstrating abnormalities in neonatal herpes simplex virus type 2.

Methodology
All patients had undergone non-contrast CT and MRI with and without contrast. HSV-2 was proven in all cases by virology or serology.

MRI examinations were performed on a 1.5-T scanner and consisted of T1, FLARE, T2 turbo spin echo sequences, post contrast T1 with magnetization transfer, and DWI with apparent diffusion coefficient maps in 10 patients. Clinical and follow-up data were evaluated as well.

Results
Clinical symptoms of patients were nonspecific, either with signs of sepsis or general neurological problems, with only 2 patients demonstrating a vesicular skin rash suggesting herpes. Only 2 cases had a maternal history of skin rash during pregnancy or delivery.

Imaging findings were multifocal in 67% (8 patients). In 33%, it was limited to either temporal lobes or brainstem and cerebellum. Temporal lobes were involved in 8 patients.

CT was normal initially in 3 of 11 patients, and questionable hypodensities were seen in 2.

Some suggestion of hemorrhage was present in 8 of 12 patients in the early stages of disease.

DWI was the most sensitive for detecting abnormalities.

Conventional MRI demonstrated more extensive disease than CT in 9 of 11 patients. DWI was the only abnormal modality in 2 of 10 patients.

In 5 of 10 patients, DWI demonstrated greater disease than that seen on MRI or CT. In 3 of 10, DWI lesions were more conspicuous but otherwise the same.

On follow-up imaging, areas with abnormal DWI but normal conventional MRI developed necrosis and encephalomalacia. Deep gray structures were clearly involved in 7 of 12 patients.

In 5 of 12 cases, there were areas of gray-white blurring or loss of differentiation or gyral or leptomeningeal enhancement on MRI.

In 4 of 10 patients, restricted diffusion was seen in watershed areas remote from the site of infection, suggesting hypoperfusion injury. In 50% of patients, disease progressed despite acyclovir treatment.

Conclusions
Diffusion-weighted imaging is the most sensitive modality for demonstrating abnormalities in neonatal herpes simplex virus type 2.

DWI plays an important role in the diagnosis of neonatal HSV-2 encephalitis. Disease can be multifocal or limited to the temporal lobes, cerebellum, or brainstem, and can cause hemorrhage and remote watershed ischemic injuries.

Reviewer’s Comments
This excellent paper answered nearly all my questions. The authors noted important findings, and pointed out previous misconceptions, such as the idea that HSV-2 doesn’t typically affect temporal lobes. In situations of neonatal illness that may be neurologic, DWI is essential.

Author: Yaron Lebovitz, MD
Reference:
Vossough A, Zimmerman RA, et al. Imaging Findings of Neonatal Herpes Simplex Virus Type 2 Encephalitis. Neuroradiology; 2008; 50 (April): 355-366

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