December 29, 2008

SUBARACHNOID HEMORRAGE - LABORATORY WORK UPS AND FINDINGS

Subarachnoid hemorrhage (SAH) implies the presence of blood within the subarachnoid space from some pathologic process. The common medical use of the term SAH refers to the nontraumatic types of hemorrhages, usually from rupture of a berry aneurysm or arteriovenous malformation (AVM). The scope of this article is limited to these nontraumatic hemorrhages.

Workup
Complete blood count
Prothrombin time, activated partial thromboplastin time
Blood typing and screening
Blood bank typing is indicated when SAH is identified or a severe bleed is suspected.
Intraoperative transfusions may be required.
Troponin I (cTnI): cTnI measurement is a powerful predictor for the occurrence of pulmonary and cardiac complications, but it does not carry additional prognostic value for clinical outcome in patients with aneurysmal SAH (Schuiling, 2005).
Imaging Studies
The initial study of choice is an urgent CT scan without contrast (see Picture 1).
Sensitivity decreases with time from onset and with older resolution scanners.
In one recent study published by New England Journal of Medicine, good quality CT scanning revealed subarachnoid hemorrhage in 100% of cases within 12 hours of onset and 93% within 24 hours of onset (Suarez, 2006). Other studies traditionally report 90-95% sensitivity within 24 hours of onset of bleeding, 80% at 3 days, and 50% at 1 week.
CT also can detect intracerebral hemorrhage, mass effect, and hydrocephalus.
A falsely negative CT scan can result from severe anemia or small-volume SAH.
Distribution of SAH can provide information about the location of an aneurysm and prognosis.
Intraparenchymal hemorrhage may occur with middle communicating artery and posterior communicating artery aneurysms. Interhemispheric and intraventricular hemorrhages may occur with anterior communicating artery aneurysms.
Outcome is worse for patients with extensive clots in basal cisterns than for those with a thin, diffuse hemorrhage.
Cerebral angiography is performed once the SAH diagnosis is made.
This study assesses the following:
Vascular anatomy
Current bleeding site
Presence of other aneurysms
This study helps plan operative options.
Angiography findings are negative in 10-20% of patients with SAHs.
If negative, some advocate repeating angiography a few weeks later.
Magnetic resonance imaging (MRI) is performed if no lesion is found on angiography.
Its sensitivity in detecting blood is considered equal or inferior to that of CT scan.
The higher cost, lower availability, and longer study time make it less optimal for detecting SAH.
MRI mostly is used to identify possible AVMs that are not visible on angiography.
MRI may miss small symptomatic lesions that have not yet ruptured.
Magnetic resonance angiography (MRA) is less sensitive than angiography in detecting vascular lesions; however, many believe CT angiography and/or MRA one day will play a more central role.
Multidetector computed tomography angiography (MD-CTA) of the intracranial vessels is now a routine examination, and it is becoming fully integrated into the imaging and treatment algorithm of patients presenting with acute subarachnoid hemorrhage in many centers in the United Kingdom and Europe (Goddard, 2005). Digital-subtraction cerebral angiography has been the criterion standard for the detection of cerebral aneurysm, but CT angiography has gained more popularity and is frequently used owing to its noninvasiveness and a sensitivity and specificity comparable to that of cerebral angiography (Jayaraman, 2004).
Other Tests
Electrocardiogram
About 20% of SAH cases have myocardial ischemia from the increased circulation of catecholamines.
Typical results are nonspecific ST-and T-wave changes, prolonged QRS segments, U waves, and increased QT intervals.
ECG changes reflect myocardial ischemia or infarction and should be treated in the usual manner. Suspicion of SAH is a contraindication to thrombolytic and anticoagulant therapy.

Lumbar puncture
Lumbar puncture (LP) is indicated if the patient has possible SAH and negative CT scan findings.
Perform CT scan prior to LP to exclude any significant intracranial mass effect or obvious intracranial bleed.
LP may be negative less than 2 hours after the bleed; LP is most sensitive at 12 hours after symptom onset.
Red blood cells (RBCs) in the cerebrospinal fluid (CSF) remain consistently elevated in 2 sequential tubes or punctures in SAH, whereas the number of RBCs in technically traumatic punctures decrease over time.
Xanthochromia (yellow-to-pink CSF supernatant) usually is seen by 12 hours after the onset of bleeding; ideally this is measured spectrographically, although many laboratories rely on visual inspection.
LP findings were thought to be positive in 5-15% of all SAH presentations that are not evident on the CT scan. This number may be no longer valid with the advent of newer generations of CT scans. A recent small retrospective chart review about patients presenting to the emergency department undergoing fifth generation CT scans and LP showed no patients with positive LP and negative CT scan (Boesiger, 2005).

REFERENCE: http://emedicine.medscape.com/article/794076-overview

No comments: