SUMMARY Three cases of a form of focal hydrocephalus are described which the authors term "entrapment of the temporal horn". Obstruction of one lateral ventricle in the region of the trigone isolates the temporal horn. Continued secretion of cerebrospinal fluid within the temporal horn causes it to behave as a mass lesion. In the cases described the causes of the condition were recurrent glioma, previous tuberculous meningitis and surgical excision of an arteriovenous malformation which extended into the trigone. Shunting of the trapped temporal horn provides satisfactory treatment.We describe three cases of a syndrome in which obstruction of the trigone of the lateral ventricle seals off the temporal horn from the rest of the ventricular system. Continued secretion of cerebro-spinal fluid by the choroid plexus within the temporal horn leads it to expand into a cyst which behaves as a mass lesion. This entity which we have termed "entrapment of the temporal horn" is a form of focal hydrocephalus, which has previously attracted little notice. It is distinct from two other rare but well recognised forms of partial hydrocephalus: unilateral hydrocephalus caused by obstruction of one foramen of Monro and septation of the ventricular system after infantile meningitis. Case reportsCase 1This 23-year-old woman had undergone resection of a right temporal malignant glioma 2 l/2 years previously followed by a course of radiotherapy. Eighteen months later a local recurrence of her tumour had been treated by further surgical resection and chemotherapy. At neither operation had the ventricular system been entered and she had been left with no neurological defect. One year later she developed severe progressive headache and drowsiness over a period of three days. On admission she was found to be confused and irri- horn which contained 60 ml of clear colourless fluid resembling cerebro-spinal fluid. The communication of the temporal horn and the trigone was severely narrowed by fibrous tissue. This stenosis was opened up so that the temporal horn communicated freely with the trigone. After operation she made a rapid recovery although she was left with a left lower facial weakness and a homonymous lower quadrantinopia. She remained well until six months later when she died from a recurrence of her tumour.

The anterior lumbar approach is not generally favoured by many neurosurgeons, despite its many advantages, due to the significant risk of vascular injuries as reported in the literature. This risk is especially acknowledged by the emerging generation of neurosurgeons with very little general surgical exposure during the training years. Adopting a combined vascular and neurosurgical approach has been reported to reduce the risk of vascular injury in anterior lumbar surgery acceptably low. This team approach provides an excellent opportunity to preserve some key 'general' surgical skills for neurosurgeons and ensure safe outcome for the patients.

Tuberculomas of the spinal cord are rare. They usually present as mass lesions with little evidence of systemic illness. We report a case where the diagnosis was only made histologically, emphasising the need to consider infection as a cause of neurological illness in patients from under-developed countries.

The camino ventricular bolt system has been used to monitor intracranial pressure in patients after severe head injury. The correlation between the ventricular pressure measured with the Camino device and an external transducer showed that the Camino accurately measured intracranial pressure over a wide range, but that it read an average of 1.15 mm Hg higher than that obtained by the external transducer. The technique has the advantage over a remote transducer because it is sited within the ventricle. This may be of value in wave-form analysis.

SUMMARY A proportion of patients with computed tomographic (CT) scan appearances of malignant brain tumour undergo conservative management, despite the absence of histological confirmation of the diagnosis. Concern that this policy risked misdiagnosing a benign tumour prompted us to examine the accuracy of CT scanning in diagnosing malignant lesions. The study was designed to determine whether within a group of 300 patients with intracerebral mass lesions of known pathology, two sub-groups existed: one with appearances so specific for malignant glioma that biopsy was unnecessary, and the other in which the appearances were characteristic of malignancy, though not specific for glioma. Three neuroradiologists independently reviewed the CT scans, together with brief clinical details. When diagnosing malignant tumours, all made errors: nine benign lesions were considered to be malignant. When diagnosing malignant glioma, one neuroradiologist made errors, but the other two adopted a more cautious approach and were accurate. The restricted a "certain" diagnosis to about one in five scans considered to show malignant tumour. Those diagnosed specifically as malignant glioma were intrinsic, irregular, mixed density lesions, exhibiting variable enhancement and infiltrating the peri-ventricular tissues, especially the corpus callosum. Using these criteria, they could correctly identify a small proportion ofpatients with malignant gliomas. In all other patients, biopsy remains the only means of obtaining a definitive diagnosis.