The CT scan: pitfalls and posterior fossa cisternography

A case of an inadequately enhanced 4-cm acoustic tumor missed by initial CT scan and diagnosed six months later on a second, different CT scanner is reported. The most common pitfall in acoustic tumor diagnosis by CT scan is the inability to resolve tumors less than 1.5 cm. This necessitates a posterior fossa cisternogram. A method of tumor size classification based on CT scan and cisternography is proposed.