The essential pathophysiological feature of dystonia is co-contraction of antagonistic muscles. This may be due to derangement of the spinal cord or cortical mechanism. In the cord, there is disruption of the normal reciprocal inhibition of antagonists during agonist contraction. This decreased reciprocal inhibition is due to reduced presynaptic inhibition of muscle afferent input to the inhibitory interneuron. The reduced presynaptic inhibition may in turn be either due to defective suprasegmental control or to changes in the tonic afferent input to the interneuron from cutaneous and muscle afferents. Alternatively, genesis of dystonia may entirely be a cortical mechanism. Overactivity of the premotor cortices, which receive projections from basal ganglia via ventral thalamus, could result in dystonia by abnormal activation of cortical motor neurons. This may again be due to a dopaminergic dysfunction of basal ganglia.

Twenty patients with foramen magnum lesions were operated upon in the last 5 years at Postgraduate Institute of Medical Education and Research, Chandigarh. The common presenting features were quadriparesis, quadriplegia, diminished sensations, neck pain and respiratory insufficiency. The lesions encountered were meningiomas, neurofibromas, posterior inferior cerebellar artery aneurysms, neurenteric cyst and chordoma. Patients with posterior or posterolaterally placed lesions were operated by the midline posterior approach while those with anterior or anterolateral lesions were managed by the far lateral approach. All mass lesions were excised completely and the aneurysms were clipped. Seventeen patients made good neurological recovery while three died. The latter three patients presented very late. The merits of various surgical approaches to the foramen magnum are discussed.

Electrodiagnostic data of fifty seven symptomatic extremities with carpal tunnel syndrome (CTS) are described. Practice recommendations made by American Academy of Neurology, American Association of Electrodiagnostic Medicine and American Academy of Physical Medicine and Rehabilitation regarding electrodiagnostic studies were considered while confirming CTS diagnosis by electrodiagnostic studies. Median sensory nerve conduction studies were the commonest abnormalities noted. The median orthodromic sensory latencies were prolonged in 86% and sensory nerve action potential amplitude abnormalities were seen in 82%. Prolongation of the conduction in the short segment across the wrist in the median nerve was seen in 96.5% and the difference in the conduction between median and ulnar nerve across the wrist was significant in all the 57 extremities. The median motor latencies were prolonged in 67% of hands. Higher incidence of electrodiagnostic abnormalities observed in this study might be due to inclusion of patients with severe disease.

Computed tomographic (CT) studies in olivopontocerebellar atrophies (OPCA) and 'early onset cerebellar ataxia with retained tendon reflexes (EOCA)' are few and vary widely in methodology and criteria for cerebellar and brainstem atrophy. In this prospective study, CT scan observations on 26 patients (EOCA-11, OPCA-15) were compared with 31 controls using qualitative and quantitative assessment of cisterns, ventricles and atrophy of brain. Vermian and/or cerebellar hemispheric (predominantly anterior) atrophy was present in 80.8% and both were equally common. Cerebral cortical atrophy (26.9%) and leukoariosis (15.4%) were less frequently seen. Statistically significant atrophy of pons, brachium pontis, cerebellum and midbrain was noted in patient group. No significant differences were observed between EOCA and OPCA groups. Evidence of atrophy did not correlate with either the duration of illness or the severity of cerebellar ataxia in both the groups. The severity of brainstem atrophy in 14 patients with and 12 patients without abnormal brainstem auditory evoked response did not differ significantly. This study highlights the methodology of CT evaluation for brainstem and cerebellar atrophy, draws attention to cerebral atrophy and emphasizes the lack of significant differences in CT morphology between OPCA and EOCA patients.

Two uncommon cases of unilateral, asymmetrical hydrocephalus secondary to membranous occlusion of foramen of monro are described. Both the cases presented with clinical features of raised intracranial pressure and their cranial computerized scans (CT) revealed asymmetrical dilatation of lateral ventricles with displacement of septum pellucidum towards the side of smaller ventricle. Neuroendoscopic fenestration of septum pellucidum and foramen of monro was tried in both the cases, which remained successful in first, while the second case required unilateral ventriculoperitoneal shunt, due to failed endoscopic negotiation of narrowed foramen of monro and intraoperative bleeding during endoscopic intervention.

Opinion is still divided over a standard surgical procedure to decompress lumbar canal stenosis. Both, laminectomy with or without facetectomy and foraminotomy and interlaminar fenestration have been advocated. In the present communication interlaminar decompression in lumbar canal stenosis has been discussed. Sixteen consecutive patients (7 males and 9 females) with clinical, neurological and radiological features of lumbar canal stenosis were treated by interlaminar (fenestration) decompression. The age of onset of symptoms ranged between 22-57 years. Adjoining lamina around interlaminar space of involved segment along with ligamentum flavum and part of facet joint (undercutting facetectomy), extending laterally (foraminotomy) were removed at single or multiple levels. Follow-up response (93.7%) over a period of two and half years showed the results as good in 73.3% and fair in 26.7% of cases, with uniformly uneventful post-operative period.

Magnetic resonance imaging findings in 13 patients with acute transverse myelitis are reviewed. In 12 cases centrally located high intensity signal extending over few spinal segments was noted. The lesion occupied more than two thirds of the cord's cross-sectional area in 8 patients. Central dot sign was noted in 7 patients. Variable cord enlargement was seen in 5 patients. Contrast study in one patient showed peripheral enhancement. The MR characteristics that help in differentiating transverse myelitis from spinal form of multiple sclerosis are discussed.

Fifty seven patients (42 males and 15 females) with non-compressive myelopathy were studied from 1997 to 1999. Acute transverse myelitis (ATM) was the commonest (31) followed by Vit B12 deficiency myelopathy (8), primary progressive multiple sclerosis (5), hereditary spastic paraplegia (3), tropical spastic paraplegia (2), subacute necrotising myelitis (1), radiation myelitis (1), syphilitic myelitis (1) and herpes zoster myelitis (1). 4 cases remained unclassified. In the ATM group, mean age was 30.35 years, antecedent event was observed in 41.9% case, 25 cases had symmetrical involvement and most of the cases had severe deficit at onset. CSF study carried out in 23 patients of ATM revealed rise in proteins (mean 147.95mg%, range 20-1200 mg/dL) and pleocytosis (mean 20.78/cumm, range 0-200 mm3). Oligoclonal band (OCB) was present in 28% of cases of ATM. The most common abnormality detected was a multisegment hyperintense lesion on T2W images, that occupied the central area on cross section. In 6 patients hyperintense signal was eccentric in location. MRI was normal in 4 cases of ATM. Thus ATM is the leading cause of non-compressive myelopathy. Clinical features combined with MRI findings are helpful in defining the cause of ATM.

Lesions in the parasellar and paracavernous regions can be removed by various skull base approaches involving basal osteotomies. A major complication of intradural skull base approaches is CSF leak and associated meningitis. We have managed 5 patients with skull base lesions with a pure extradural approach using wide basal osteotomies. The operative techniques are described.

We report the findings on CT and MR imaging in a patient with rapidly progressive subacute sclerosing panencephalitis (SSPE), which correlated with the clinical progression of the disease. In view of the rapid neurological deterioration and CSF pleocytosis, a brain biopsy was done and this confirmed the diagnosis.

Two unusual cases of thoracic spinal canal stenosis are reported. The cord compression was a result of unilateral hypertrophy of the lamina and facet joint. Bony decompression resulted in rapid neurological recovery.

Although rare, extracranial extension of a meningioma has been well documented. An interesting natural history of neglected meningioma with skull vault hyperostosis and predominantly extracranial extension is described. Following surgical resection of the highly vascular meningioma, the patient developed fatal coagulopathy.

Malignant rhabdoid tumours (MRT) are extremely malignant, highly aggressive and uncommon renal neoplasms of childhood with very poor prognosis. About fifteen cases of primary intracranial MRT (with their clinical details) are reported in English literature, following the recognition of this entity in 1978. Two cases of MRT are reported here. The first case, one year male baby was admitted with a very large, infiltrative, posterior fossa mass. He required elective ventilation, following the tumour decompression but ultimately died of respiratory failure during the process of weaning from the ventilator. The second child was operated for an extremely vascular, very friable, solid and lobulated tumour of temporal lobe. Radical microsurgical decompression of mass was achieved, however the child developed massive recurrence, documented five weeks after the surgery while on radiotherapy. His recurrence showed partial response to radiotherapy and chemotherapy. The child is alive at 8 month's follow up, but probably passing the terminal days of his life. Hence the recognition of this entity is very essential for the aggressive management and prognostication of the patient, which obviously seems to be different from primitive neuroectodermal tumour.

A 50 year old female who was operated for atrial septal defect 8 years back, presented with clinical features suggestive of subarachnoid haemorrhage (grade I, Hunt and Hess). CT scan of brain revealed haemorrhage in all the supratentorial basal cisterns, sylvian cistern and small haematoma in the left occipital lobe. Conventional CT and MR angiography revealed aneurysm in relation to distal part of the calcarine branch of the left posterior cerebral artery (PCA). Left occipital craniotomy in prone position followed by deep dissection in the occipital lobe showed fusiform aneurysm of the distal part of the calcarine branch. PCA aneurysms constitute only 0.2 to 1% of all intracranial aneurysms and among them distal PCA aneurysms are most rare, constituting only 1.3%. They too are mostly seen at the bifurcation of the PCA. The present case however, is unique in the sense that it has developed as a fusiform aneurysm in the distal part of the calcarine branch. To the best of our knowledge this is rare among the rarest.

An intracranial mixed germ cell tumour with germinoma and teratoma components is reported. The patient presented with parinaud's syndrome and precocious puberty. The treatment involved partial surgical debulking followed by whole brain radiotherapy (4500 cGY in 25 fraction over 5 weeks) and chemotherapy (consisting of cisplatin and etoposide). Post treatment MRI showed no residual lesion. The controversies in the management are discussed.

We report three patients with pyomyositis due to Staphylococcus aureus. Magnetic resonance imaging aided in the accurate diagnosis of the infection and of the extent of involvement. Incision, drainage and antibiotic therapy eradicated the infection in all the patients. We suggest clinical or subclinical bacteraemic seeding of the diseased muscle, as the most likely mechanism for pyomyositis.

Ventricles can be involved in different ways in neurotuberculosis, however, the occurrence of intraventricular abscess has been rarely reported. We report a young woman who had intraventricular tubercular abscess. Cranial computed tomographic scan showed hypodense ring enhancing lesion in the right lateral ventricle with unilateral hydrocephalus. She underwent parasagittal craniotomy with total excision of the lesion. The pus obtained from the lesion was teeming with acid fast bacilli.

A case of benign osteoblastoma affecting posterior element of spine with pain and paraplegia in a female is being presented with brief review of literature. Early diagnosis and surgical excision remains the mainstay of treatment.

A 29 year old male with primary generalized seizures for 13 years stopped his anticonvulsants leading to an increase in seizure frequency. Five months later he developed a severe manic episode postictally which responded well to a combination of neuroleptics and anticonvulsants. Postictal psychoses usually follow complex partial seizures. Manic episodes are uncommon. This case had some similarities with other cases of postictal psychoses reported previously. It underlines the need for further investigation of several facets of this complex relationship between mood disorders and epilepsy.

A case of infantile onset Alexander's disease in a two and a half year old male child is presented, who had progressively increasing macrencephaly since birth. A frontal lobe biopsy revealed collections of Rosenthal fibres in the subpial and perivascular areas with diffuse dysmyelination and presence of reactive astrocytes. The Rosenthal fibres were immunoreactive for glial fibrillary acidic protein and ubiquitin. Electron microscopic examination showed the Rosenthal fibres as intra-astrocytic and extracellular granular osmiphilic collections.

A patient with bilateral subdural haematomas in association with idiopathic thrombocytopenic purpura is documented. She was managed successfully with platelet rich plasma and immunosuppressive therapy with steroids.