Pneumorrhachis (PR), the presence of intraspinal air, is an exceptional but eminent radiographic finding, accompanied by different aetiologies and possible pathways of air entry into the spinal canal. By reviewing the literature and analysing a personal case of traumatic cervical PR after head injury, we present current data regarding the pathoanatomy, clinical and radiological presentation, diagnosis and differential diagnosis and treatment modalities of patients with PR and associated pathologies to highlight this uncommon phenomenon and outline aetiology-based guidelines for the practical management of PR. Air within the spinal canal can be divided into primary and secondary PR, descriptively classified into extra- or intradural PR and aetiologically subsumed into iatrogenic, traumatic and nontraumatic PR. Intraspinal air is usually found isolated not only in the cervical, thoracic and, less frequently, the lumbosacral regions but can also be located in the entire spinal canal. PR is almost exceptional associated with further air distributions in the body. The pathogenesis and aetiologies of PR are multifold and can be a diagnostic challenge. The diagnostic procedure should include spinal CT, the imaging tool of choice. PR has to be differentiated from free intraspinal gas collections and the coexistence of air and gas within the spinal canal has to be considered differential diagnostically. PR usually represents an asymptomatic epiphenomenon but can also be symptomatic by itself as well as by its underlying pathology. The latter, although often severe, might be concealed and has to be examined carefully to enable adequate patient treatment. The management of PR has to be individualized and frequently requires a multidisciplinary regime.

The data demonstrate the dynamics of brain shift and the limits of conventional neuronavigation and add additional support for the unavoidable inaccuracy of contemporary neuronavigational systems once the cranium is opened. Brain shift leads to a significant loss of reliability of neuronavigation systems during microsurgical removal of intracranial lesions and there are differences of the course and the amount of brain shift in relation to special subgroups of supratentorial cerebral lesions. However, because of the heterogeneous nature of lesions neurosurgeons have to remove, the modest quantity of shared common variance, and the differences between superficial and subcortical brain shift, it seems unlikely that the amount and course of brain shift become exactly predictable pre-operatively. Only an intra-operative update of image data should have the capacity to overcome this fundamental problem of modern neuronavigation.

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Objectives-Although there is general agreement that surgery is the best treatment for chronic subdural haematoma (CSDH), the extent of the surgical intervention is not well defined. Methods-The less invasive surgical technique of bedside percutaneous subdural tapping and spontaneous haematoma efflux after twist drill craniostomy under local anaesthesia was prospectively analysed in 118 adult patients, 99 with unilateral and 19 with bilateral CSDH. Results-The mean number of subdural tappings was 3.2. Ninety two of the patients with unilateral CSDH were successfully treated by up to five subdural tappings, 95% of the patients with bilateral CSDH were successfully treated by up to 10 subdural tappings. The mean duration of inpatient treatment was 12 days. In 11 patients (9%) the treatment protocol had to be abandoned because of two acute subdural bleedings, two subdural empyemas, and seven cases of insuYcient haematoma eZux and no neurological improvement. The only significant predictor for failure of the described treatment protocol was septation visible on preoperative CT. Conclusions-The described therapy protocol is-apart from a purely conservative treatment-the least invasive presently available surgical technique for treating chronic subdural haematoma. Its results are comparable with other modern treatment protocols. Thus, it can be recommended in all patients as a first and minimally invasive therapy, especially in patients in a poor general condition. Patients with septation visible on preoperative CT should be excluded from this form of treatment. (J Neurol Neurosurg Psychiatry 2000;69:40-47)

MRI is the diagnostic procedure of first choice because of its potential to demonstrate the exact localisation, extent and relationship of the arachnoid cyst to the spinal cord. Cord atrophy secondary to compression can be visualised and used for prediction of neurological outcome. Myelography and CT-Myelography (CTM) are still of diagnostic value since they might demonstrate the communication between the subarachnoid space and the cyst, which is important for surgical planning. The aim of surgical treatment is neural decompression and prevention of refilling of the cyst which is best accomplished by complete resection of the cyst and closure of the communication between cyst and subarachnoid space.