Subarachnoid hemorrhage CT scan findings

Patients with subarachnoid hemorrhage need to undergo CT examination to understand the situation, including head CT. If CT cannot provide evidence of subarachnoid hemorrhage, then head MRI can be used as a diagnostic method.

1. Head CT: It is the preferred method for diagnosing SAH. CT showing high-density shadows in the subarachnoid space can confirm SAH. Based on the CT results, the location of the intracranial aneurysm can be preliminarily determined or suggested: for example, if it is located in the internal carotid artery segment, it is often asymmetric blood accumulation in the suprasellar cistern; in the middle cerebral artery segment, blood accumulation is often seen in the lateral fissure; in the anterior communicating artery segment, blood accumulation is seen at the base of the anterior fissure; and if bleeding occurs in the interpeduncular cistern and circular cistern, there is generally no aneurysm. Dynamic CT examinations can also help understand the absorption of bleeding, whether there is rebleeding, secondary cerebral infarction, hydrocephalus and its degree, etc. The sensitivity of CT for the diagnosis of subarachnoid hemorrhage is 90-95% within 24 hours, 80% within 3 days, and 50% within 1 week.

1. Head MRI: When the sensitivity of CT decreases a few days after the onset of illness, MRI can play a greater role. After 4 days, T1 images can clearly show extravasated blood, and the high blood signal can last for at least 2 weeks, and even longer on FLAIR images. Therefore, when CT cannot provide evidence of subarachnoid hemorrhage 1-2 weeks after the onset of the disease, MRI can be used as an important method for diagnosing subarachnoid hemorrhage and understanding the site of ruptured aneurysm.

2. Cerebrospinal fluid (CSF) examination

Usually, lumbar puncture is not a routine clinical examination for patients who have been diagnosed by CT examination. If the amount of bleeding is small or the onset time is long, CT examination may not show positive findings, but clinical suspicion of inferior vena cava hemorrhage requires lumbar puncture to examine CSF. It is best to perform lumbar puncture 12 hours after onset to facilitate identification of accidental injury. Uniformly bloody cerebrospinal fluid is a characteristic manifestation of subarachnoid hemorrhage and indicates fresh bleeding. If CSF turns yellow or phagocytic cells containing red blood cells, hemosiderin or bilirubin crystals are found, it indicates that SAH has existed for different periods of time.