Comparison of myelography with CT follow-up versus gadolinium MRI for subarachnoid metastatic disease in children. We evaluated 17 children with primary intracranial neoplasms for subarachnoid metastatic disease (SAMD) using myelography with computed tomographic follow-up (Myelo + CT) and cerebrospinal fluid (CSF) histopathologic examination, as well as magnetic resonance imaging with gadolinium DTPA (MRI + Gd), between December 1988 and December 1989. There were 12 boys, and the median age was 5.7 years (range, 0.8 to 21.8 years). Tumor histology included 8 primitive neuroectodermal tumors (PNETs), 3 ependymomas, 2 low-grade astrocytomas, 1 anaplastic astrocytoma, 1 glioblastoma multiforme, 1 atypical rhabdoid tumor, and 1 malignant fibrous histiocytoma. Thirteen tumors originated in the posterior fossa, 2 were supratentorial, and 2 were in the spinal cord. The median interval between the 2 diagnostic tests was 2 days. MRI + Gd was positive in 11 (65%), Myelo + CT in 8 (47%), and CSF in 5 (29%) cases. MRI + Gd was superior in delineating spinal cord nodules and "sugar coating" whereas Myelo + CT more readily revealed nerve root sleeve filling defects. There was no case in which Myelo + CT was positive that MRI + Gd did not reveal SAMD. MRI + Gd is a safe, noninvasive test that should be used as the initial imaging modality for the presence of SAMD. 