MR imaging of syringobulbia.

The magnetic resonance (MR) examinations of 65 patients with syringomyelia were evaluated to determine the incidence and MR characteristics of syringobulbia. Syringobulbia was identified in 11 patients (17%), 10 of whom had communicating syringomyelia (associated with the Chiari I malformation) and one idiopathic syringomyelia. The cavities extended from 5 to 20 mm above the plane of the foramen magnum. Two types of syringobulbia were identified. The 10 patients with Chiari I malformation had thin clefts or slits extending into the medulla. These cavities were much smaller than the cervical cavities. The other patient had saccular syringobulbia in which the medullary cavity was similar to the cervical syrinx cavity. The T1-weighted images were most useful in detection of syringobulbic cavities. The theory of syringobulbia development and a brief review of the literature are included.