Parkinsonism and midbrain dysfunction after shunt placement for obstructive hydrocephalus.

We report a patient in whom placement of a ventriculoperitoneal shunt for obstructive hydrocephalus secondary to non-neoplastic aqueductal stenosis was complicated by progressive parkinsonism and midbrain dysfunction. These sequelae were refractory to treatment, including shunt revision and levodopa therapy. These findings contradict the opinion from the literature that this type of parkinsonism is a reversible condition and levodopa therapy is effective for managing the symptoms. We discuss the pathophysiological mechanism of this complication.

Odontoid compression of the brainstem without basilar impression-- "odontoid invagination".

We report five patients with odontoid invagination, in which the odontoid process bulges upward into the foramen magnum and compresses the brainstem without deformity of the occipital bone. Two patients had a craniovertebral abnormality associated with Chiari malformation without instability of the craniovertebral junction (stable odontoid invagination). The other three patients had dislocation of the craniovertebral junction due to iatrogenic destruction of the occipital condyle, rheumatoid arthritis or an anomaly of C2 (unstable odontoid invagination). Patients with stable odontoid invagination underwent a transoral odontoidectomy followed by occipitocervical fixation. Those with unstable odontoid invagination underwent cervical traction followed by posterior fixation in reducible cases, while in irreducible cases odontoidectomy with subsequent occipitocervical fixation was performed. Decompression of the neuraxis together with symptomatic improvement was achieved in all patients and none became unstable or developed new symptoms during follow-up ranging from 3 to 15 years.

Surgical experience of syringomyelia with reference to the findings of magnetic resonance imaging.

We present our surgical experience of 20 patients with syringomyelia, who were divided into two groups based on the findings of magnetic resonance (MR) imaging: a "non-visible cisterna magna" group, in which MR imaging did not reveal cerebrospinal fluid (CSF) in the cisterna magna, and a "visible cisterna magna" group. Patients with non-visible cisterna magna were associated with Chiari malformation (14 patients) or tight cisterna magna (4 patients) and underwent craniocervical decompression. Intradural exploration was performed when CSF movement in the cisterna magna or CSF outflow from the fourth ventricle appeared to be insufficient. It is important to confirm CSF outflow from the foramen of Magendie. Patients with visible cisterna magna were associated with tuberculous meningitis (2 patients) and underwent shunting procedures. Postoperatively, improvement in symptoms and a reduction in syrinx size were demonstrated in all patients except one. Two patients experienced recurrence of symptoms and syrinx dilatation.

Syringomyelia without hindbrain herniation: tight cisterna magna. Report of four cases and a review of the literature.

Idiopathic syringomyelia, which is not associated with any definite pathogenic lesions, has been treated mainly by shunting of the syrinx and rarely by craniocervical decompression. The authors report four cases of syringomyelia thought to be idiopathic syringomyelia but treated by craniocervical decompression with favorable results. Syringomyelia was present without hindbrain herniation. In such cases, the subarachnoid space anterior to the brainstem at the level of the foramen magnum is usually open but the cisterna magna is impacted by the tonsils, a condition the authors term "tight cisterna magna." All patients underwent foramen magnum decompression and C-1 laminectomy, and the outer layer of the dura was peeled off. Further intradural exploration was performed when outflow of cerebrospinal fluid (CSF) from the fourth ventricle was deemed to be insufficient. Postoperatively, improvement in symptoms and a reduction in syrinx size were demonstrated in three patients, and a reduction in ventricle size was shown in two. Syringomyelia associated with tight cisterna magna should not be classified as idiopathic syringomyelia; rather, it belongs to the category of organic syringomyelia such as Chiari malformation. A possible pathogenesis of cavitation is obstruction of the CSF outflow from the foramen of Magendie, and the cavity may be a communicating dilation of the central canal. Ventricular dilation may depend on the extent to which CSF drainage is impaired from the foramina of Luschka. These cavities may respond to craniocervical decompression if it results in sufficient CSF outflow from the foramen of Magendie, even in cases with concomitant hydrocephalus.