From the Guidelines
The Middle Cerebral Artery (MCA) territory can be identified on a CT brain scan by looking for frank hypodensity within the first 6 hours, involvement of one third or more of the MCA territory, and early midline shift, as these are useful in predicting cerebral edema 1.
Key CT Findings
- Frank hypodensity on head CT within the first 6 hours
- Involvement of one third or more of the MCA territory
- Early midline shift
- Hyperdense MCA sign, which represents the thrombus, can be seen in one third to one half of all cases of angiographically proven thrombosis 1
CT Scan Protocol
- Noncontrast CT scan with contiguous, discrete (nonhelical) images from the vertex of the calvarium through the foramen magnum
- Sections that are 5 mm thick are preferred, but scans should not be thicker than 10 mm
- The scan plane should be parallel to the canthal meatal line 1
Additional Imaging Modalities
- CT angiography can be used to cover the entire cerebrovascular axis, including the anterior (carotid) and posterior (vertebrobasilar) circulation, as well as the extracerebral carotid arteries
- Dynamic CT perfusion scan can be used to assess tissue perfusion and evaluate collateral flow 1
From the Research
Identifying Middle Cerebral Artery (MCA) Territory on CT Brain
To identify the MCA territory on a CT brain scan, several early signs can be looked for, including:
CT Signs in Deep MCA Territories
In the deep MCA territories, early CT signs can be divided into three grades:
- Grade I: Normal basal ganglia with hypodensity localized to the insula 3
- Grade II: Partial obscuration of the posterolateral part of the putamen 3
- Grade III: Hypodensity of the entire lentiform nucleus 3
Improved CT Diagnosis
The use of density-difference analysis can improve the detection rate of acute MCA territory infarcts on CT scans 4. This method involves histograph analysis of density values and digital subtraction of the histogram of one hemisphere from the other.
Bilateral Hyperdense Middle Cerebral Arteries
Bilateral hyperdense middle cerebral arteries can be a sign of acute thromboembolic disease, even in the absence of other radiographic evidence of acute stroke 5. CT angiography can confirm bilateral MCA, M1 segment vascular occlusion, and follow-up noncontrast CT can demonstrate MCA territory infarctions.
Predictive Value of Early CT Signs
Early CT signs can be predictive of subsequent infarct locations and outcome 2. The presence of two or three early parenchymatous signs (ALN, LIR, or HSE) is associated with extended MCA infarct and poor outcome.
Limitations of CT
It is worth noting that MRI has superior capabilities for the detection of cerebral infarcts compared with CT 6. However, CT can still be a useful tool in evaluating the early prognosis of MCA infarction and selecting better treatments.