Comparison of CT scan and MRI findings in the diagnosis of Japanese encephalitis
Introduction
The neurotropic viruses have special predilection for specific areas of central nervous system e.g. herpes simplex for frontotemporal cortex, polio for anterior horn cells and herpes zoster for dorsal root ganglia. Most of the flavi viruses have been shown to affect subcortical gray matter such as thalamus, basal ganglia, substantia nigra and cerebellum [1], [2]. There is paucity of reports on radiological changes in Japanese encephalitis [3], [4], [5], [6], [7], [8]. The first report of CT scan in Japanese encephalitis (JE) revealed low density areas in thalamus, basal ganglia and substantia nigra [8]. Similar changes were also reported in 2 neonates with JE [9]. MRI changes in JE were first reported in a 73-year-old lady who had hyperintense signal changes on T2 in thalamus, insula, hippocampus and putamen [7]. Subsequent MRI studies in patients with JE reported thalamic hyperintensity on T2 sequence [4], [5], [6]. These studies however were based on small number of patients. In our initial studies, we reported characteristic bilateral thalamic lesions in JE and emphasised the diagnostic value of these changes in the area where JE is endemic [5]. In the diagnosis of herpes simplex encephalitis (HSE), MRI has been reported to be more sensitive than CT Scan and regarded as the investigation of first choice [10]. A comparison of CT and MRI findings in JE has not been reported so far. We, therefore, present a comparison of CT scan and MRI findings and discuss these changes in the light of reported histopathological findings.
Section snippets
Patients and methods
Forty two patients with Japanese encephalitis examined by us during 1992–1998 have been included. The patients presenting with encephalitic symptoms, having four fold rise in IgG antibody titres against JE virus assessed by haemagglutination inhibition test were diagnosed as JE. Neurological evaluation including mental status, cranial nerves, motor and sensory systems were carried out. Blood counts, serum chemistry, blood smear examination for malarial parasite, CSF examination for cell,
Results
Our observations are based on 42 patients with JE and 40 of whom fulfilled all the inclusion criteria. In two patients, haemagglutination inhibition titres did not show 4 fold rise. The mean age of the patients was 22 (range 2–60) year and 14 were females. There were 13 children whose age was below 13 years. the mean Glasgow coma scale score was 6.0 (range 3–8). Thirteen patients had seizures in the acute stage. Eight of these patients died; 2 in the first week, 4 within 1 month and 2 after 2
Discussion
In our study, MRI was abnormal in all the patients with Japanese encephalitis whereas CT scan was abnormal in 21 patients only. On MRI, the changes were noted in thalamus (94%), basal ganglia (35.5%), midbrain (58%), cerebellum (25.8%), pons (19%) and cerebral cortex (19%). Japanese encephalitis primarily affects diencephalon and mesencephalon; however, brainstem, cerebellum and cerebral cortex are also affected [11]. The limitation of CT scan in revealing the brainstem and posterior fossa
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