Hidden dense middle cerebral artery sign in a 4-year-old boy with traumatic subarachnoid hemorrhage.

A 4-year-old boy was admitted with acute onset of hemiplegia of the right side that was secondary to a traffic accident. Initial computed tomography revealed a traumatic subarachnoid hemorrhage, and follow-up computed tomography showed a more localized hematoma of the left sylvian cistern. After a few days of conservative treatment, magnetic resonance imaging (MRI) revealed a cerebral infarction of the left lenticulostriate territory, even though magnetic resonance angiography showed preserved middle cerebral artery flow. Thus, we realized that the hematoma of the sylvian cistern was the so-called dense middle cerebral artery sign. This case of posttraumatic infarction suggested the importance of meticulous investigations and clinical correlations of imaging studies in pediatric patients with head injuries.