A previously healthy 4-year-old boy from a small village in Mexico developed acute onset of nausea, vomiting and headache. He had no perinatal complications, normal developmental milestones and complete immunizations for his age. There was no history of exposure to animals. He was evaluated at a local primary health care center where paracetamol and ranitidine were prescribed. The patient had partial relief, but on day 13 of illness, he experienced left ptosis, diplopia and abdominal pain. He was referred to the tertiary health care center but no specific diagnosis was made, and no medications were prescribed. On day 17 of illness, he developed ataxic gait, abnormal eye movements, dysarthria and worsening of his headache. He had no history of fever, sore throat, diarrhea or skin rash. On day 21 of illness, the patient presented to the emergency department and was admitted to the hospital. He had a temperature 37°C axillary, heart rate of 90 beats/min, respiratory rate of 25 breaths/min, blood pressure of 110/60 mmHg and oxygen saturation 95% in ambient air. The patient was conscious and interacting with his parents but had difficulty in speaking. Neurological examination showed bilateral third and fourth nerve palsies, anisocoria, unilateral mydriasis, dysmetria and dysdiadochokinesia. Reflexes and muscle strength were diminished in the left leg and normal in the right leg and both arms. The fundoscopic examination revealed mild bilateral papilledema. The neck was supple without lymphadenopathy. Lungs were clear. Cardiovascular examination was normal. The abdomen was soft without hepatosplenomegaly.
Laboratory studies on admission revealed white blood cell count of 9950/mm3, with a differential count of 58% segmented neutrophils, 30% lymphocytes, 10% monocytes and 2% eosinophils, hemoglobin of 12.5 gm/dL and platelet count of 255,000/mm3. Erythrocyte sedimentation rate was 8 mm/h and C-reactive protein was 0.5 mg/dL. A complete metabolic panel, coagulation studies and urinalysis were normal. Lumbar puncture, HIV testing and immunological studies were not performed.
A chest radiograph was normal. A contrast-enhanced computed tomography scan of the brain showed an ill-defined, irregular, hyperdense cerebellar mass displacing the fourth ventricle. Magnetic resonance imaging on axial FLAIR and T2 weighted sequences showed a hyperintense lesion with severe surrounding edema in the left cerebellar hemisphere, displacing the brainstem and fourth ventricle (Fig. 1). Based on these imaging findings, a posterior fossa tumor was suspected.
The patient underwent craniotomy and resection of two-thirds of the tumor mass. After surgery, the child was admitted to the Pediatric Intensive Care Unit under sedation and supported by mechanical ventilation. On the first postoperative day, the child developed generalized seizures, which were attributed to the neurosurgical procedure, and treatment with phenytoin was started. On the second postoperative day, he developed signs of increased intracranial pressure with increasing systolic blood pressure, bradycardia, mydriasis and unresponsive pupils. An emergent noncontrast computed tomography of the head revealed hydrocephalus and multiple hypodense parenchymal lesions with perilesional edema in parietal lobe of the left hemisphere and the frontal, parietal and occipital lobes of the right hemisphere. A ventriculoperitoneal shunt was placed.
Histopathology and immunohistochemical studies of the brain biopsy showed no evidence of medulloblastoma. However, a granulomatous inflammatory process with multinucleated giant cells was present, and in addition, round structures felt to be consistent with Histoplasma capsulatum were seen. Based on these findings, histoplasmosis of the central nervous system became the presumptive diagnosis, and treatment with amphotericin B and dexamethasone was started. Despite all efforts, the patient deteriorated and died 2 days after surgery. Biopsy specimens were reviewed again, and the true diagnosis was established postmortem.