Chandra N. Sen

An Extreme Lateral Approach to Intradural Lesions of the Cervical Spine and Foramen Magnum

Meningiomas and neurofibromas are the most common intradural extramedullary tumors of the foramen magnum and cervical spine. Many of these tumors are located ventral or ventrolateral to the spinal cord and medulla. Posterior approaches, although adequate for the management of most of these tumors, can sometimes result in incomplete removal of the tumor and exacerbation of the neurological deficits. Although the transoral and transcervical approaches provide a direct route to the tumor, the exposure of the lateral margins in the case of large tumors is inadequate. In addition, because of the removal of vertebral bodies, subsequent fusion may be necessary. In the present report, an extreme lateral approach to the foramen magnum and cervical spine for the removal of intradural tumors is described. The approach provides a lateral exposure of the tumor-cord/stem interface, thus permitting safe dissection without retraction of the cord. The entire longitudinal and lateral extent of the tumor and also its extradural extension can be can be managed by this approach. This approach can be considered in such a group of patients harboring entirely ventral or recurrent tumors for which the conventional posterior approach has failed. Six patients who underwent this procedure are described to illustrate its application.

Anterior cranial base reconstruction : role of galeal and pericranial flaps

Reconstruction of surgical defects in 30 patients undergoing surgery of the anterior cranial base was performed using pericranial, galeopericranial, and galeal scalp flaps. Twenty‐seven patients had resection of neoplasms, the majority of which were malignant. Fifty‐seven percent of patients received prior therapy consisting of surgery and/or radiotherapy. Adequate healing of the cranial base was noted in all cases without persistent cerebrospinal fluid leaks, meningitis, or brain herniation. Mucosalization of the intranasal surface was noted. No skin grafts were used. At a median follow‐up of 13 months, 67% of patients were alive with no evidence of disease.

Chordoma and chondrosarcoma of the cranial base: an 8-year experience

Between 1980 and 1988, 8 patients with chordomas and 9 with low-grade chondrosarcomas involving the cranial base were treated. All the patients were investigated preoperatively and postoperatively with computed tomographic or magnetic resonance imaging scans, according to a standard protocol. The tu

Facial Translocation: A New Approach to the Cranial Base

Nasopharynx, clivus, and cavernous sinus are difficult regions of the cranial base in which to perform oncologic surgery. We have developed an approach to this area by using facial soft tissue translocation and craniofacial osteotomies. Surgical field obtained at the skull base can extend from the contralateral eustachian tube to ipsilateral geniculate ganglion. It includes the nasopharynx, clivus, sphenoid, and cavernous sinus, as well as the entire infratemporal fossa and superior orbital fissure. Our experience with this technique in 12 patients is reported. All patients healed primarily.

The results of surgery for benign tumors of the cavernous sinus.

CAVERNOUS SINUS SURGERY has been performed increasingly in the last 2 decades because of new knowledge and technologies. With increasing international expertise in cavernous sinus surgery, the results must be analyzed critically to search for accurate prognosticators of outcome. We performed a retrospective review of 124 patients (40 male, 84 female; mean age, 45 years) who underwent cavernous sinus surgery for benign tumors from 1983 to 1992. Sixty-five percent had tumors encasing the internal carotid artery. Mean follow-up was 29 months (median, 26 mo). Gross total or near-total resection was possible in 80%. Patients with neurilemomas, angiofibromas, epidermoids, chondroblastomas, and hemangiomas were more likely to have total or near-total resection (100% versus 75%, P < 0.025). Disabling complications (five cerebral infarctions, two meningitis, and one hydrocephalus with chiasmal prolapse) occurred only in patients with meningiomas or pituitary adenomas. On follow-up, excellent/good binocular vision was achieved in 53% of patients entering surgery with excellent/good function versus 25% who entered surgery with fair/poor binocular vision (P < 0.025). Ninety-three percent of patients had a Karnofsky score > or = 70 on follow-up. There were a total of 12 recurrences (10%), 6 in patients with meningiomas, 2 in patients with angiofibromas, 2 in patients with craniopharyngiomas, 1 in a patient with a pituitary adenoma, and 1 in a patient with an osteoblastoma. Patients with tumor growth or neurological symptoms indicative of progressive cavernous sinus involvement should undergo cavernous sinus exploration. This surgery has acceptable morbidity and mortality and, if the tumor can be removed easily, the surgeon should try to perform radical tumor resection. To avoid major complications, the surgeon must exercise utmost care to preserve the neurovascular structures of the cavernous sinus, with special attention to tumors that extend into the petroclival region. Better results from surgery can be expected in those patients with neurilemomas, hemangiomas, or epidermoids than in patients with meningiomas, craniopharyngiomas, or pituitary adenomas. Good functional outcome can be expected, particularly if the patients preoperative clinical status is good. Particular attention must be paid to the reconstruction of anatomic barriers in order to prevent cerebrospinal fluid leakage and subsequent meningitis.

Chordomas and chondrosarcomas involving the cavernous sinus: Review of surgical treatment and outcome in 31 patients

During the last 9 years, 31 patients with chordomas (20 cases) and chondrosarcomas (11 cases) involving the cavernous sinus have been treated using an aggressive surgical approach. On the basis of postoperative magnetic resonance imaging (MRI), 17 patients were considered to have undergone total removal, whereas in the remaining 14 cases the tumor was either subtotally or partially removed. Surgical complications were most commonly encountered among patients who had undergone previous operations. One patient died 3 months after the operation as a result of pulmonary embolism. Significant disability occurred in one patient because of thalamic perforator occlusion and hemorrhage. Recovery of extraocular muscle function was gratifying, and correlated to the preoperative functional level. After a median follow-up of 24 months, three recurrences (21%) occurred among the 14 patients who had undergone incomplete removal. No recurrence was observed among the 17 patients with total resection. This experience shows that gross radical removal of chordomas and chondrosarcomas involving the cavernous sinus can be accomplished with an acceptable surgical morbidity. However, much longer follow-up will be required to determine whether such aggressive surgical treatment results in cure or long-term control of these neoplasms.

Recordings from the facial nucleus in the rat: signs of abnormal facial muscle response

SummaryOn the basis of results of electrophysiological studies in patients undergoing microvascular decompression (MVD) operations to relieve hemifacial spasm (HFS), we have postulated that the abnormal muscle response characteristically found in patients with HFS is the result of irritation of the facial nerve by the blood vessel that is compressing the facial nerve near its exit from the brainstem in these patients. This abnormal muscle response is seen when one branch of the facial nerve is electrically stimulated and recordings are made from muscles that are innervated by other branches of the facial nerve. We further hypothesized that the facial nucleus is hyperactive in patients with HFS and that the spasm and the abnormal muscle response are results of a phenomenon known as “kindling”. These hypotheses are supported by recent studies showing that chronic electrical stimulation of the facial nerve trunk in rats near the brainstem results in an abnormal muscle response that is similar to that seen in patients with HFS. In this paper, we present the results of recording from the facial motonucleus in rats that had been subjected to repeated electrical stimulation of the facial nerve. The results indicate that the abnormal muscle response in these rats was caused by changes in the function of the facial motonucleus. We interpret these results as showing that the physiological abnormalities that give rise to the signs of HFS in man are located in the facial motonucleus, and that the changes in the function of the nucleus are produced by chronic antidromic neural activity resulting from close contact between a blood vessel and the facial nerve.

Responses from dorsal column nuclei (DCN) in the monkey to stimulation of upper and lower limbs and spinal cord

Responses from the dorsal surface of the exposed dorsal column nuclei (DCN) in baboons and a monkey (Macaca fascicularis) were recorded in response to electrical stimulation of the posterior tibial nerve at the ankle, the common peroneal nerve at the knee, the sciatic nerve, the spinal cord at T10, and the median nerve at the wrist. Recordings of far-field potentials from the vertex with a non-cephalic reference were made before exposing the DCN and simultaneously with recordings from the DCN. The response recorded from the DCN using a monopolar electrode to median nerve stimulation was a negative deflection (N wave) followed by a large and slow positive wave (P wave). The N wave was often preceded by a small positive deflection. The response from the median nerve to electrical stimulation of the DCN had the same latency as the initial positive peak and the initial portion of the N wave in the response from the DCN to stimulation of the median nerve, indicating that the initial positive peak was generated by presynaptic events in the DCN. The response recorded from the surface of the DCN to stimulation of the lower limbs consisted of many irregular waves followed by a large, positive deflection. Sometimes these irregular waves were superimposed on a small negative peak, and they were preceded by a positive deflection. The response from the tibial nerve to stimulation of the DCN consisted of a series of waves that had the same latency as the waves of the response from the DCN to stimulation of the tibial nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of somatosensory evoked potentials recorded from the scalp and dorsal column nuclei to upper and lower limb stimulation in the rat

Responses from the dorsal column nuclei (DCN) in the rat to stimulation of the upper limbs (median nerve) and lower limbs (sciatic nerve) showed a difference in the wave forms of the two responses. These results support results of earlier studies in the cat, monkey, and man that showed that only slow-conducting cutaneous afferents from the lower limbs travel in the dorsal column, while all afferents from the upper limbs travel in the dorsal column and synapse in the DCN. A comparison between the response from the DCN and that from the vertex to stimulation of the upper limbs showed correspondence between short-latency peaks, while no clear earlier waves could be discerned in the response from the vertex to stimulation of the lower limbs. Even when the dorsal column was transected on one side, the correspondence between the early peaks in the scalp and the DCN responses to stimulation of the upper limbs was maintained. The effect of the dorsal column lesion on the response recorded from the surface of the DCN to stimulation of the sciatic nerve was mainly a reduction in the number of peaks. Transection at the midbrain level resulted in elimination of the long-latency response in the scalp recording, but the initial negative peak was maintained, which corresponded to the initial negative peak of the DCN response to stimulation of the upper limbs.

Facial nerve management in cranial base surgery

This study reviewed 124 patients who required facial nerve manipulation during cranial base surgery. Most of them underwent only nerve displacement or selective transection for improved surgical access to the cranial base (70 and 34, respectively). Fourteen patients had the facial nerve resected for oncologic reasons and repaired with primary nerve grafting. Most patients regained quite satisfactory facial function with quality correlating with the degree of nerve injury. Six patients had facial nerve resected as part of oncologic palliation and had the facial deficit rehabilitated with regional tissue.