Intraoperative computerized tomography scanning to assess the adequacy of decompression in anterior cervical spine surgery.

OBJECT: The purpose of this study was to improve the accuracy of bone removal during anterior spinal surgery. Intraoperative computerized tomography (CT) scanning was used to assess the success of bone resection and permit immediate correction in the event of inadequate bone removal. METHODS: The Phillips Tomoscan M was used to obtain preoperative cervical scans before and after cervical bone resection was complete. The completeness of bone removal was assessed by the operating neurosurgeon by reviewing the postresection CT scan. If the bone removal was deemed inadequate, additional bone was removed using a high-speed drill. A CT scan was obtained after each subsequent decompression until adequate bone removal was achieved. In 31 patients undergoing anterior cervical decompression intraoperative CT scanning was performed. Nineteen patients underwent corpectomy and 12 discectomy. Of the 31 patients, assessment of intraoperative CT scans obtained in 17 indicated further bone removal was required. CONCLUSIONS: Intraoperative CT scanning to monitor bone removal during anterior cervical surgery is a valuable tool to ensure the adequacy of surgery.

Endoscopically assisted prevention of cerebrospinal fluid leak in suboccipital acoustic neuroma surgery.

HYPOTHESIS: The purpose of this prospective study was to determine if direct inspection of air cells using endoscopy could reduce the occurrence of cerebrospinal fluid (CSF) leak in suboccipital acoustic neuroma surgery. BACKGROUND: Cerebrospinal fluid leak remains one of the most common complications after acoustic neuroma surgery. The suboccipital approach for excision of acoustic neuromas has been used increasingly since gadolinium-enhanced magnetic resonance imaging has improved the ability to diagnose smaller tumors. Suboccipital approaches are reported to have CSF leak rates of as high as 27% with an average rate of 12%, most presenting as rhinorrhea. Ideally, this complication could be avoided by careful closure of all air cells exposed during the approach, especially those commonly found in the posterior wall of the internal auditory canal and in the retrosigmoid area. Packing these cells with a variety of materials has been done but often indirectly, as visualization of all cells by the conventional operating microscopes may not be possible. Failure to recognize patent cells because of limited visualization may be an important cause of postoperative CSF leak. METHODS: This study compared CSF rhinorrhea rates of 38 consecutive suboccipital acoustic neuroma operations, in which conventional techniques were used to pack the temporal bone defect around the internal auditory canal, with the succeeding 24 consecutive operations, in which endoscopes were used to visualize all exposed air cells directly. After locating all patent air cells endoscopically, they were specifically sealed with bone wax, and then a small fat graft harvested from the wound margin was used to fill the remaining defect. RESULTS: Postoperative CSF rhinorrhea occurred in 7 of 38 (18.4%) operations in which no endoscopic technique was used and in 0 of 24 operations in which endoscopes were used. CONCLUSIONS: The use of endoscopes to visualize the temporal bone air cells that cannot be directly observed otherwise appears to reduce the incidence of postoperative CSF leak in suboccipital acoustic neuroma surgery.

Translabyrinthine drillout from suboccipital approach to acoustic neuroma.

The suboccipital approach to acoustic neuroma surgery is used when preservation of hearing is desired or when the surgeon prefers the approach even when hearing cannot be saved. its major disadvantages are poor exposure of the lateral internal auditory canal and lack of precise bony landmarks to identify the facial nerve. When hopes for preservation of hearing are abandoned and complete removal of tumor is considered paramount, a wider drillout of the posterior temporal bone may be accomplished through the suboccipital approach. The posterior semicircular canal may be opened and followed into the vestibule. A translabyrinthine exposure of the vertical crest and full length of the internal auditory canal is readily obtained. Translabyrinthine drillout procedures were performed in 14 patients, and the technique was expedient and yielded excellent exposure. An abdominal fat graft was not required, and only one instance of leakage of cerebrospinal fluid occurred. Translabyrinthine drillout from the suboccipital approach is a useful adjunct when sacrifice of hearing is indicated.

Cochlear nerve conduction block: an explanation for spontaneous hearing return after acoustic tumor surgery.

In the presence of an intact cochlear nerve, hearing loss has been attributed to either transection or spasm of the internal auditory artery or direct mechanical trauma to the cochlear nerve during tumor manipulation. Such events have been correlated with changes in intraoperative auditory evoked potentials. The possibility of a reversible conduction block in the cochlear nerve, however, has not been investigated. Review of four cases of delayed spontaneous recovery of hearing several months after acoustic tumor resection suggests that a conduction block phenomenon may exist. By comparing recent pertinent animal data with clinical intraoperative electrophysiologic data obtained during posterior fossa surgery in human subjects, we attempt to elucidate further the pathophysiology and intraoperative predisposing factors to cochlear nerve injury during hearing preservation procedures.

Myelopathy due to intracranial dural arteriovenous fistulas draining intrathecally into spinal medullary veins. Report of three cases.

Arteriovenous malformations (AVM's) of the spine commonly cause progressive myelopathy. Occasionally, myelography reveals serpentine filling defects characteristic of a spinal AVM, but an AVM or arteriovenous (AV) fistula cannot be demonstrated arteriographically, despite selective catheterization of all vessels known to have the potential of supplying the spinal cord and spinal dura. Often, and particularly in the setting of subacute or acute deterioration, this has been attributed to spontaneous thrombosis of the veins (the Foix-Alajouanine syndrome). Three patients are reported in whom intracranial dural AV fistulas, supplied by branches of the internal and external carotid arteries, drained into spinal veins and produced myelopathy. In one patient, motor and sensory deficits were limited to the lower extremities. In all three patients, disconnection of the fistula from its spinal venous drainage permitted arrest of a rapidly progressive myelopathy and partial recovery. These findings indicate that some patients who appear to have spinal cord AVM's but exhibit negative spinal arteriography are suffering from cranial dural AV fistulas and therefore need carotid as well as spinal arteriography. The considerable distance of these fistulas from the level of neurological expression supports venous hypertension as a pathophysiological mechanism of spinal cord injury. Interruption of a cranial dural fistula draining into spinal veins permits recovery of the myelopathy.

Specificity of muscle reinnervation after epineurial and individual fascicular suture of the rat sciatic nerve.

We experimentally analyzed the specificity of muscle reinnervation after suture and regeneration of rat sciatic nerve. We used a horseradish peroxidase (HRP) technique of axon tracing to compare the number and location of motoneurons that innervate muscle via the peroneal nerve after epineurial and individual fascicular suture of the parent sciatic nerve. These motoneurons are significantly reduced in number from control levels and are often in spinal cord locations that indicate previous innervation of antagonistic muscle via the tibial nerve. This inappropriate reinnervation of peroneal muscle by tibial motoneurons is minimized by individual fascicular suture without compromise of overall reinnervation. Our findings thus support the hypothesis that individual fascicular suture may avoid distortion of the central connections of peripheral units.