SUMMARY It has been increasingly recognised that patients with arachnoid cysts of the middle fossa appear more susceptible to the development of subdural haematomas. Seven patients with arachnoid cysts of the middle fossa and associated subdural haematomas are presented. Intra-cystic haemorrhage, masking the presence of an arachnoid cyst on computed tomography (CT) is highlighted. Repeat of CT scanning in young patients with subdural haematomas in the absence of severe trauma is recommended. Two theories are proposed to account for the observed susceptibility to the development of subdural haematomas in these patients. A 15 year old male was admitted with a 4 week history of right parietal headache, 3 days vomiting and increasing paraesthesia involving the left arm. Three months previously he had been kicked over the left parietal region and as a result struck his right parietal region against a wall. Clinical examination revealed bilateral papilloedema, nystagmus and a slow pulse. Plain skull radiographs showed expansion of the right middle fossa. Computed tomography (CT) demonstrated a right middle fossa arachnoid cyst with a large subdural haematoma and midline shift to the left. At craniotomy a large chronic subdural haematoma extending from the frontal to the occipital pole and overlaying the arachnoid cyst on the right was found. There was a haematoma within the cyst. All dural membrane surrounding the haematoma and part of that of the arachnoid cyst was removed. There was steady clinical improvement paralleled by radiological resolution and a reduction in the size of the arachnoid cyst. The latter was no longer visible on CT scan 3 years later.Case 2 A 17 year old male was referred with a history of a few days of increasing occipital headache radiating to the back of the neck, and intermittent episodes of vomiting. He had been known to have suffered severe headaches at approximately monthly intervals for some years. No record of head injury was given on direct questioning. Clinical examination was unremarkable, plain film radiography of the skull revealed enlargement of the right middle fossa. CT scan showed an arachnoid cyst in the right middle fossa with a subdural haematoma lying superficial to it. Haemorrhage was noted in the arachnoid cyst. Operation confirmed the above findings showing a chronic haematoma overlying an arachnoid cyst.

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We describe two patients with neurofibromatosis, each of whom was found to have an arteriovenous malformation (AVM), an uncommon manifestation of the disease, presenting as an extradural space-occupying lesion in the cervical spine. In one patient the finding of an unsuspected AVM at operation led to massive blood loss; in the other magnetic resonance imaging (MRI) of the neck allowed the diagnosis to be made and the hazard of an operation to be avoided. Solid tumours that may occur in the disease of neurofibromatosis are known to cause neurological deficits as the result of space occupation. We wish to draw attention to another pathological entity which may cause neurological deficits: that of AVMs. We also propose that in the investigation of such a patient MRI be borne in mind as a non-invasive radiological tool, particularly as, hopefully, its cost reduces and its availability becomes more widespread.