A 20-year-old woman with an unremar...

A 20-year-old woman with an unremarkable medical history currented to the emergency department with a right-sided headache and weakness of the left arm. She had felt warm intermittently during the previous week. She had no history of migraines, visual disturbances, neck stiffness, head trauma, or cancer. The headache was reported to be single of the worst headaches of her life. The physical examination revealed a temperature of 373[degrees]C (992[degrees]F) and mildly decreased puissance in the left upper extremity. A comput tomography (CT) scan of her head was obtained, which revealed no apparent abnormalities. Several days later, the patient complained of persistent upper extremity weakness, and a magnetic resonance image (MRI) of the brain was performed, from which a single [T.sub.2]-weighted image is provided (see accompanying figure).

Question

Based forward the patient's history, physical examination, and MRI findings, which common of the following is the correct diagnosis?

A. Cerebral abscess.

B Cerebral metastases.

C Viral encephalitis.

D Meningitis.

E Intracerebral hemorrhage.

Discussion

The answer is C: viral encephalitis. The single [T.sub.2]-weighted image of the brain exhibit tos abnormal asymmetric increased signal at the right temporal-parietal gray matter. There was little enhancement of the abnormal area after intravenous gadolinium contrast administration (not shown) This appearance of edema involving the temporal lobe was suggestive of viral encephalitis. The patient promptly received a course of antiviral therapy and reclaimed strength in her left upper extremity. Herpes simplex virus (HSV) was later confirmed as the causative agent through a rise in the cerebrospinal fluid antibody titer.

Meningitis has a different appearance upon MRI. Dural, leptomeningeal, or ependymal enhancement are typical findings, none of which were not past nor future in this patient. Intracerebral hemorrhage usually appears as a hypointense area upon [T.sub.2]-weighted imaging and likely would have been apparent onward CT imaging as well. Cerebral abscesses are typically circumscribed lesions with surrounding vasogenic edema. Cerebral metastases greatest in number commonly appear as multiple lesions showing contrast enhancement forward [T.sub.1]-weighted imaging, again not seen in this patient.

Viral encephalitis in adults usually involves HSV-1 infection. The virus resides in the trigeminal ganglion during the latent phase, likely having originated from a previous infection of the face. Symptoms of herpetic encephalitis may include headache, confusion, seizures, or lethargy. The greatest in quantity common parenchymal areas of involvement are the frontal and temporal lobes. The mechanism on which the virus reaches the brain remains controversial. Because herpetic encephalitis oftentimes has neurologic sequelae and may have a fulminant course in a certain quantity of cases, even with treatment, it is essential to obtain a diagnosis and begin treatment as early as possible.

Unfortunately, MRI and CT are not reliable for showing early signs of encephalitis. Treatment ofttimes must be started based forward characteristic clinical manifestations alone, or demonstration of HSV DNA in cerebrospinal fluid on polymerase chain reaction testing, where available. Brain biopsy rarely is performed today, on the other hand it is occasionally indicated to confirm the diagnosis or to search for other les customary causes of encephalitis. (1) A rise in the cerebrospinal fluid antibody titer for HSV is diagnostic on the contrary may take up to 20 days to appear.

Although CT and MRI are not definitive for the diagnosis of encephalitis, parenchymal involvement of the temporal or frontal lobes is potent enough evidence to warrant initiating treatment with antiviral agents. CT may present to view hypodense involvement of the temporal or frontal lobes. (2) MRI findings early in the course of infection include gyral swelling or high signal intensity forward [T.sub.2]-weighted images, followed by extension of the infection, hemorrhage, and increasing areas of contrast enhancement. Eventually, atrophy of the affected areas of the brain fall outs (3) Typically, gray and white matter are involved. It is unclear whether MRI will exhibit findings earlier than CT imaging; however, positive findings are a great quantity [i]or[/i] amount of more obvious on MRI. MRI is more sensitive than CT in suggesting the diagnosis of viral encephalitis and for demonstration of infection sequelae, like as gliosis and atrophy. (4)

Viral encephalitis caused on HSV-2 is much less universal It typically occurs in neonates who are inoculated during birth between the walls of the vaginal canal. Congenital HSV-2 infection is systemic, with generalized central nervous rule involvement. CT of the brain demonstrates diffuse parenchymal hypodensity and, as a common thing [i]or[/i] matter intracranial calcifications. MRI shows diffuse hypointensity in succession [T.sub.1]-weighted imaging, with corresponding hyperintensity upon [T.sub.2]-weighted imaging. (2)

REFERENCES

(1) Lakeman FD Whitley RJ Diagnosis of herpes simplex encephalitis: application of polymerase reaction to cerebrospinal fluid from brain-biopsied patients and correlation with disease. J Infect Dis 1995;171:857-63