Omar Bennett
The hyperdense middle cerebral artery sign (HMCAS) is a radiological marker of intra-arterial thromboembolism and can provide an early diagnosis to identify ischemia before the infarct becomes visible and before brain damage develops. It is the earliest visible sign of MCA infarction and is seen within 90 minutes after the event. The hyperdense MCA sign refers to an appearance of increased attenuation of the proximal middle cerebral artery (MCA) that is often associated with thrombosis of the M1 MCA segment and may be the only diagnostic feature on computed tomography early after ischaemic stroke. False positives are recognized, and correct recognition of this sign is important with the advent of thrombolytic therapy for stroke.
| Characteristics | Values |
|---|---|
| Hyperdense Middle Cerebral Artery Sign | Hyperdense MCA sign, Gacs sign |
| Type | Hyperdense vessel sign |
| Refers to | Increased attenuation of the proximal middle cerebral artery (MCA) |
| Seen in | Thrombosis of the M1 MCA segment |
| Diagnosis | Ischaemic stroke |
| CT Appearance | Focal hyperattenuation of the MCA on non-contrast brain CT |
| Cause | Intraluminal thromboembolic material |
| Seen within | 90 minutes after the event |
| Clot location | Proximal MCA |
| Clot composition | High globin concentration |
| Clot response | Recanalization therapy, thrombolysis, endovascular clot retrieval |
| MCA ratio | >1.2 |
| Absolute density | >43 HU |
| Retrospective study period | January 2015 to April 2021 |
| Study centre | West China Hospital, SCU |
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What You'll Learn
The hyperdense MCA sign is a type of hyperdense vessel sign
The hyperdense MCA sign, also known as the Gacs sign, is a type of hyperdense vessel sign. It is a radiological marker of intra-arterial thromboembolism and can be used to provide an early diagnosis and identify ischemia. It is caused by an embolic red blood clot arising from the heart or arteries. The high attenuation is caused by the high globin concentration in the clot. The clot usually lodges in the proximal MCA.
The hyperdense MCA sign is generally transient, but it can be stable in cases of vascular wall calcification. It is an insensitive but specific sign suggestive of vascular thrombosis in patients presenting with ischemic stroke. The presence of a true hyperdense sign can be confirmed by measuring the attenuation value as compared to the normal-appearing contralateral side. The sensitivity of this CT sign for embolism is only about 30%, but its specificity is about 90%.
The hyperdense MCA sign is the earliest visible sign of MCA infarction and is seen within 90 minutes after the event. It is associated with a heavy clot burden, which can cause obstruction of the orifices of arteries for leptomeningeal collateral flows and lead to severe clinical conditions. The thrombus volumes are larger and longer in patients who have the hyperdense sign than in those without.
To determine the most accurate way to detect infarction using the hyperdense MCA sign, 87 patients with suspected infarction underwent non-enhanced CT brain scans. The maximum density was determined on the suspected affected side and the contralateral side, and a ratio was made. A follow-up CT was then done to detect MCA territory infarction. The HU range of the affected MCA ranged from 44 up to 58 HU (mean value 49.62 HU). The mean value of MCA ratio was 1.24-1.55.
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It refers to the focal hyperattenuation of the middle cerebral artery
The hyperdense middle cerebral artery (MCA) sign, also known as the Gacs sign, refers to the focal hyperattenuation of the middle cerebral artery. It is a type of hyperdense vessel sign, indicating an occluding clot in acute ischaemic stroke. This sign is often observed within 90 minutes of the stroke event and is considered one of the earliest visible radiological markers for early diagnosis and identification of ischemia.
The hyperdense MCA sign is characterised by increased attenuation of the proximal middle cerebral artery (MCA), which is associated with thrombosis of the M1 MCA segment. This sign is typically detected using computed tomography (CT) scans, particularly non-contrast CT (NCCT) scans. On these scans, the hyperdense MCA appears as a linear hyperdensity in the M1 segment of the MCA. The specificity of this sign is high, at around 95%, while its sensitivity is moderate at 52%.
The focal hyperattenuation of the MCA is caused by the presence of an embolic red blood clot arising from the heart or arteries. The high attenuation is predominantly due to the high globin concentration in the clot. The clot usually lodges in the proximal MCA, sometimes protruding into the terminal supraclinoid internal carotid artery. In contrast, smaller white clot emboli tend to lodge in the M1 or M2 segments and are not visible on NCCT scans as they have similar attenuation to blood.
The hyperdense MCA sign is an important diagnostic tool as it can help distinguish between normal vessels and false positives in cases of acute ischaemic stroke. By measuring the absolute attenuation of affected and normal vessels, with an absolute density of >43 Hounsfield units (HU) and an MCA ratio of >1.2, radiologists can confirm hyperdensity and exclude other pathologies. This distinction is crucial as false positives can lead to incorrect diagnoses and treatment approaches.
In summary, the focal hyperattenuation of the middle cerebral artery, referred to as the hyperdense MCA sign, is a critical radiological marker for the early detection of ischemia and the presence of occluding clots in acute ischaemic stroke. This sign aids in distinguishing between normal vessels and false positives, thereby guiding appropriate patient care and treatment decisions.
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It is the earliest visible sign of MCA infarction
The hyperdense middle cerebral artery (MCA) sign, also known as the Gacs sign, is a type of hyperdense vessel sign. It is the earliest visible sign of MCA infarction and is seen within 90 minutes after the event. It is caused by an embolic red blood clot arising from the heart or arteries. The clot usually lodges in the proximal MCA, protruding into the terminal supraclinoid internal carotid artery. This results in focal hyperattenuation of the MCA on non-contrast brain CT.
The high attenuation is predominantly caused by the high globin concentration in the clot. By contrast, smaller white clot emboli typically lodge in the M1 or M2 segments and are not visible on non-contrast CT. These globin-poor clots have similar attenuation to blood. The sensitivity of this CT sign for embolism is about 30%, but its specificity is about 90%.
The hyperdense MCA sign is an important radiological marker for early diagnosis and identification of ischemia. It is associated with a heavy clot burden, which can cause obstruction of the orifices of arteries for leptomeningeal collateral flows and lead to severe clinical conditions. The thrombus volumes are larger and longer in patients with the hyperdense sign, suggesting that the sign is closely related to the collaterals and angioarchitecture in acute ischemic stroke.
To distinguish hyperdense MCAs associated with acute ischaemic stroke from normal vessels and false positives, the absolute attenuation of affected and normal vessels must be measured. An absolute density of >43 Hounsfield units (HU) and an MCA ratio of >1.2 define hyperdensity and exclude all other pathologies.
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It is associated with acute ischaemic stroke
The hyperdense middle cerebral artery (MCA) sign is an early marker of acute ischaemic stroke. It is a type of hyperdense vessel sign, referring to the appearance of increased attenuation of the proximal MCA, which is often associated with thrombosis of the M1 MCA segment. This can be identified through computed tomography (CT) and is considered the earliest visible sign of MCA infarction, occurring within 90 minutes of the event.
The hyperdense MCA sign is associated with acute ischaemic stroke and can be distinguished from normal vessels and false positives by measuring the absolute attenuation of affected and normal vessels. An absolute density of >43 Hounsfield units (HU) and an MCA ratio of >1.2 indicate hyperdensity and exclude all other pathologies. This distinction is important as false positives have been recognised, and the correct recognition of the hyperdense MCA sign is crucial with the advent of thrombolytic therapy for stroke.
The hyperdense MCA sign is caused by an embolic red blood clot arising from the heart or arteries. The high attenuation is predominantly caused by the high globin concentration in the clot. The clot usually lodges in the proximal MCA, protruding into the terminal supraclinoid internal carotid artery. This can result in occlusion of the MCA, which may lead to severe clinical conditions.
The presence of the hyperdense MCA sign is associated with a poor clinical outcome in stroke patients treated with intravenous recombinant tissue plasminogen activator (tPA). However, it remains uncertain whether the presence of the hyperdense MCA sign is directly associated with acute neurological deterioration after tPA treatment.
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It is a radiological marker of intra-arterial thromboembolism
The hyperdense middle cerebral artery sign (HMCAS) is a radiological marker of intra-arterial thromboembolism. It is a type of hyperdense vessel sign that refers to the focal hyperattenuation of the middle cerebral artery (MCA) on non-contrast brain CT. This is due to the presence of an intraluminal thromboembolic material, which is often a red blood clot arising from the heart or arteries.
HMCAS is an early marker that helps provide an early diagnosis and identify ischemia. It is the earliest visible sign of MCA infarction and is seen within 90 minutes of the event. The clot typically lodges in the proximal MCA, protruding into the terminal supraclinoid internal carotid artery. This can cause obstruction of the orifices of arteries for leptomeningeal collateral flows, leading to severe clinical conditions.
The sensitivity of the CT sign for embolism is about 30%, while its specificity is approximately 90%. The high attenuation seen in HMCAS is predominantly caused by the high globin concentration in the clot. The hyperdense vessel sign was first described by Gyula Gács.
HMCAS is associated with a heavy clot burden in ischemic stroke. The thrombus volumes are larger and longer in patients with the hyperdense sign than in those without. This can be visualised on early non-contrast computed tomographic (NCCT) scans, which show a region of hyperdensity compared to the artery on the opposite side.
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Frequently asked questions
The hyperdense middle cerebral artery sign (HMCAS) is a radiological marker of intra-arterial thromboembolism and can provide an early diagnosis to identify ischemia before the infarct becomes visible and before brain damage develops.
The hyperdense middle cerebral artery sign is an important marker in detecting acute arterial thrombotic occlusion and is one of the earliest signs of ischemic cerebrovascular accident (CVA).
The hyperdense middle cerebral artery sign is detected by non-contrast computed tomographic (NCCT) scans, which visualise a region of hyperdensity in comparison to the artery on the contralateral side.
