Haemorrhage into an arachnoid cyst: a serious complication of minor head trauma.

Arachnoid cysts are infra-arachnoidal cerebrospinal fluid collections that are usually asymptomatic. However, they can become acutely symptomatic because of haemorrhage and cyst enlargement, which may result from minor head trauma. The range of symptoms is wide and many are "soft" signs. Diagnosis is important as cysts causing mass effect require surgery. A case is reported of a child presenting with localised headaches after minor head trauma. Computed tomography demonstrated an arachnoid cyst with evidence of haemorrhage, which required surgical intervention. Other cases of arachnoid cyst presenting to our hospital or reported in the literature are reviewed with respect to presenting symptoms and signs. Localised headaches, behavioural or cognitive changes and ataxia are more commonly associated with this disorder than nausea, vomiting, visual disturbances or seizures. This range of symptomatology following minor head trauma may warrant computed tomography when other criteria for this investigation are not met.

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Intracranial arachnoid cysts are relatively rare, comprising 1% of all intracranial mass lesions, (1) of which 75% occur in children. They are benign collections of cerebrospinal fluid that are usually primary developmental abnormalities. Most are asymptomatic and found incidentally, most commonly in the middle cranial fossa and more frequently on the left side, however they may become acutely symptomatic after minor head trauma. Cysts may rupture or intracystic vessels may bleed into the cyst cavity resulting in mass effect and onset of symptoms. This may be associated with a subdural haematoma. The diagnosis is usually apparent on computed tomography although a subacute haemorrhage may appear isodense with adjacent brain tissue and require magnetic resonance imaging. (2) The treatment for arachnoid cysts with intracystic haematoma is surgical decompression and marsupialisation of the cyst. (3)

CASE REPORT

A 2 year old previously healthy boy, with normal development, presented eight days after a minor head injury. He had fallen 5-6 feet from a climbing frame onto a wood chip floor but had seemed so well after the incident that no medical attention was sought.

However, his parents noticed a new and unusual pattern of behaviour: on running or jumping he would stop suddenly and hold his left temporal region complaining of pain.

He had had no vomiting, visual disturbance or seizures. Neurological examination and fundoscopy were normal. A non-contrast CT scan demonstrated a left sided arachnoid cyst with evidence of bleeding into the cyst cavity (fig 1).