neurologic disorders
Subarachnoid Hemorrhage (SAH)
Diagnosis of Subarachnoid Hemorrhage
Usually noncontrast CT and, if negative, lumbar puncture Diagnosis of subarachnoid hemorrhage is suggested by characteristic symptoms. Testing should proceed as rapidly as possible, before damage becomes irreversible. Noncontrast CT is done within 6 hours of symptom onset. When done within this time frame, this test has very high sensitivity. Therefore, if this test does not detect a subarachnoid hemorrhage, no other testing is needed as long as patients have a normal physical examination, no meningeal signs, and no anemia, MRI is comparably sensitive but less likely to be immediately available. False-negative results occur if volume of blood is small or if the patient is so anemic that blood is isodense with brain tissue. If subarachnoid hemorrhage is suspected clinically but not identified by neuroimaging or if neuroimaging is not immediately available, Lumbar Puncture (Spinal Tap) is done. Lumbar puncture is contraindicated if increased intracranial pressure is suspected because the sudden decrease in cerebrospinal (CSF) pressure may lessen the tamponade of a clot on the ruptured aneurysm, causing further bleeding. Suspect subarachnoid hemorrhage if headache reaches peak, severe intensity within seconds of onset or causes loss of consciousness. Do lumbar puncture if subarachnoid hemorrhage is suspected clinically but CT shows no hemorrhage or is not available; however, lumbar puncture is contraindicated if increased intracranial pressure is suspected. CSF findings suggesting subarachnoid hemorrhage include Numerous red blood cells (RBCs) Xanthochromia Increased pressure RBCs in CSF may also be caused by traumatic lumbar puncture. Traumatic lumbar puncture is suspected if the RBC count decreases in tubes of CSF drawn sequentially during the same lumbar puncture. About 6 hours or more after a subarachnoid hemorrhage, RBCs become crenated and lyse, resulting in a xanthochromic CSF supernatant and visible crenated RBCs (noted during microscopic CSF examination); these findings usually indicate that subarachnoid hemorrhage preceded the lumbar puncture. If there is still doubt, hemorrhage should be assumed, or the lumbar puncture should be repeated in 8 to 12 hours. In patients with subarachnoid hemorrhage, conventional cerebral angiography is done as soon as possible after the initial bleeding episode; alternatives include magnetic resonance angiography and CT angiography. All 4 arteries (2 carotid and 2 vertebral arteries) should be injected because up to 20% of patients (mostly women) have multiple aneurysms. On ECG, subarachnoid hemorrhage may cause ST-segment elevation or depression. It can cause syncope, mimicking myocardial infarction. Other possible ECG abnormalities include prolongation of the QRS or QT intervals and peaking or deep, symmetric inversion of T waves. 