An infant in whom contrast-enhanced fluid attenuated inversion recovery (FLAIR) MRI was useful for the diagnosis of meningitis and devising a treatment strategy.

A 3-month-old male was brought to our hospital due to fever, poor sucking, and a bulging anterior fontanel. His general condition was poor. Analysis of the cerebrospinal fluid (CSF) showed increases in the cell count (8/μl) and the polymorphonuclear leukocyte count (2/μl) but normal sugar (66 mg/dl) and protein (28 mg/dl) levels. A CSF smear showed no bacterial cells. The administration of antibacterial drugs was initiated, and head MRI was performed on the next day. Plain images revealed no abnormalities. However, contrast-enhanced fluid-attenuated inversion recovery (FLAIR) MRI showed clear contrast enhancement along the brain surface in the meninges of the left and right frontal and left parietal lobes and fluid retention accompanied by contrast enhancement in a part of the adjacent subdural space. These findings could be confirmed only by contrast-enhanced FLAIR MRI. A diagnosis of bacterial meningitis with an unknown cause was made, and the administration of 2 antibacterial drugs was continued. MRI on day 8 of the illness showed the disappearance of contrast enhancement, and plain FLAIR also facilitated a diagnosis of a subdural hygroma. The treatment was effective. At present, the patient is 1 year and 6 months old without sequelae. The diagnosis of bacterial meningitis in infants is difficult based on only symptoms. In its early stage with few abnormal findings in the CSF, diagnosis is sometimes difficult. Antibacterial drug administration should be immediately initiated. However, definite findings are necessary for the continuation of large amounts of antibacterial drugs. Contrast-enhanced FLAIR allows the sensitive visualization of meningeal inflammation and is useful as a complementary diagnostic method for meningitis. In addition, this technique can reveal marked inflammatory lesions such as a subdural hygroma in the early stage, providing information useful for making a diagnosis of bacterial meningitis.