Walsh & Hoyt: Saccular Aneurysms: Diagnosis

The diagnosis of aneurysmal SAH should be suspected in any patient with the acute onset ofheadache, change in mentation or a stiff neck. Lumbar puncture once was the mainstay of diagnosis in such patients, but it has been replaced to some extent by CT scanning or MR imaging for several reasons. Withdrawal of CSF in a patient with an intracerebral hematoma may precipitate brain shift and herniation. It may be difficult to distinguish SAH from a traumatic tap. Third, neuroimaging studies often provide significant information about the origin and extent of intracranial hemorrhage that may be helpful in the initial management of the patient. Finally, hemorrhage may be loculated (arachnoid cyst or adjacent tumor) and may thus result in a false-negative lumbar puncture, although the finding of a lymphocytic pleocytosis in a patient clinically suspected of having experienced an SAH may be significant.