Early CT detection of intracranial seeding from medulloblastoma.

Since 1975, intracranial subarachnoid metastases of medulloblastoma have been detected in seven of 23 initial contrast-enhanced computed tomographic (CT) scans in children with proven medulloblastoma. Furthermore, four of the seven cases with subarachnoid seeding were diagnosed after the introduction of high-resolution contrast-enhanced CT. Only three cases of seeding had been detected in the previous 17 low-resolution cases studied with CT. Thus, it is quite likely that the incidence of subarachnoid metastases may be substantially more than the overall figure of 30% indicated by this series. This may have an impact on the treatment of these patients, since the frequent appearance of metastases may indicate the need for more vigorous chemotherapeutic regimens. One should be aware of the possibility of early intracranial subarachnoid seeding and that it can be demonstrated by contrast-enhanced CT. This is particularly true when using high-resolution scanners in conjunction with 5 mm sections through the posterior fossa.