The Resolution of Syringohydromyelia Without Hindbrain Herniation After Posterior Fossa Decompression

Bermans J. Iskandar, M.D., Gary L. Hedlund, D.O., Paul A. Grabb, M.D., W. Jerry Oakes, M.D., Division of Pediatric Neurosurgery and Department of Pediatric Imaging, Children's Hospital, Birmingham, Alabama

Neurosurg Focus. 2000;8(3) 

In This Article

Clinical Material and Methods

This study is a retrospective review of five patients with syringohydromyelia that lacked a hindbrain herniation, all of whom were treated with craniocervical decompression.

Preoperative Work-Up

Complete craniospinal imaging was performed preoperatively to rule out other causes of syringohydromyelia. Magnetic resonance (MR) images of the entire spine were obtained to rule out occult spinal dysraphism. All MR imaging was performed with and without gadolinium-diethylenetriamine pentaacetic acid to evaluate the possibility of spinal cord tumor or arachnoiditis as a cause of syringohydromyelia. In addition, all patients underwent cranial imaging (computerized tomography [CT] or MR imaging) to identify hydrocephalus or other associated brain anomalies. The presence of ventral craniocervical anomalies was also investigated on MR imaging. The technique of cine two-dimensional (2-D) phase-contrast flow analysis (cine MR imaging) was used to assess flow around the foramen magnum in the four patients most recently treated.

Surgical Procedure

All patients underwent craniocervical decompression as previously described.[11] This consisted of a suboccipital craniectomy, C-1 laminectomy, duraplasty, and the assurance of good flow from the foramen of Magendie; this often necessitated an intradural lysis of adhesions and opening of a fourth ventricular veil. On occasion, we reduced one of the cerebellar tonsils to further expand the outlet foramen.

Follow-Up Review

The patients were followed closely to check for symptomatic and neurological improvement. Postoperative MR images were obtained to assess the size of the syrinx in all five patients, and postoperative cine MR imaging was performed in four of them.

Estimation of Syrinx Size

Although the syrinx volume is the most precise estimate of its size, the irregularity of this structure made it difficult to obtain reliable measurements. Therefore, the ratio of the surface area of syrinx to spinal cord was measured using the formula r2 for surface area, with r being the radius. In addition, the diameter ratio was obtained at the level of maximum expansion to provide a simpler method of measurement. Pre- and postoperative ratios were compared at corresponding anatomical locations.

Magnetic Resonance Imaging Techniques

The MR images were obtained by using a 1.5-tesla scanner (General Electric Medical Systems, Milwaukee, WI). Our standard MR protocol consisted of spin-echo T1-weighted sequences in sagittal and axial orientations and fast spin-echo images in the sagittal plane. To supplement this protocol all patients received intravenous gadopentetate dimeglumine (0.5 mmol/kg body weight) to rule out occult tumor as a cause of syringohydromyelia. The craniocaudal extent, morphological appearance, width, and anteroposterior dimension of the syrinx were recorded.

Cine MR Imaging (Video clips: Normal or Abnormal)

In addition to standard spin-echo techniques, we performed cerebrospinal fluid (CSF) flow dynamic studies with the 2-D phase-contrast cine MR technique, which uses the motion-sensitive nature of MR imaging to demonstrate flow dynamics at the craniocervical junction. Normal CSF movement is relatively synchronous with arterial pulsations.[9,13] We performed qualitative analysis of flow pre- and postoperatively. Lack of flow was seen as an intermediate shade of gray, cranial-to-caudal flow as high signal intensity (white) and caudocranial flow as low signal intensity (black).[7]