The dense artery sign, also known as the hyperdense artery sign, is a radiological finding observed on non‑contrast computed tomography (CT) of the head. It denotes an abnormally increased attenuation (brightness) of an intracranial arterial vessel—most commonly the proximal segment of the middle cerebral artery (MCA)—and is indicative of an acute intraluminal thrombus or embolus causing arterial occlusion.
Definition and Appearance
- Definition: A focal area of increased density within an intracranial artery on non‑contrast CT that exceeds the attenuation of adjacent brain parenchyma and veins.
- Typical Appearance: The affected artery appears brighter (hyperdense) than surrounding structures, often measuring > 45 Hounsfield units (HU). The sign is usually best seen on axial CT slices and may involve the MCA, basilar artery, or other major cerebral vessels.
Clinical Context
- Stroke Diagnosis: The sign is most frequently associated with acute ischemic stroke, particularly in the early minutes to hours after symptom onset, before the development of parenchymal changes such as cytotoxic edema.
- Prognostic Significance: Presence of the dense artery sign correlates with larger infarct volumes, higher likelihood of early neurological deterioration, and reduced rates of spontaneous recanalization. It often guides emergent therapeutic decisions, including intravenous thrombolysis or endovascular thrombectomy.
Imaging Technique and Sensitivity
- Modality: Non‑contrast CT head performed within the first few hours of symptom onset.
- Sensitivity/Specificity: Reported sensitivities range from 30 % to 60 % for detecting arterial occlusion, while specificity exceeds 90 % when the sign is present. Sensitivity improves with thin‑section CT and modern multi‑detector scanners.
- Differential Diagnosis: Calcified atherosclerotic plaque, vessel wall hemorrhage, or beam‑hardening artifacts can mimic the sign; correlation with clinical presentation and, when necessary, further imaging (CT angiography or MR angiography) is required.
Pathophysiology
The increased attenuation results from the high protein and red‑blood‑cell content of an acute thrombus, which attenuates X‑rays more than flowing blood or surrounding brain tissue. Over time, as the clot undergoes organization and the density normalizes, the sign may disappear, even if the vessel remains occluded.
Historical Perspective
The dense artery sign was first described in the 1980s in the context of early CT imaging of acute stroke. Early reports highlighted its potential as a rapid, bedside indicator of large‑vessel occlusion before the widespread availability of CT angiography.
Related Radiologic Signs
- Hyperdense MCA sign: Specific term for a dense MCA segment.
- Dot sign: Hyperdensity seen within lenticulostriate branches, suggestive of small‑vessel thrombus.
- White cerebral artery sign: Alternate nomenclature occasionally used in older literature.
Clinical Management Implications
- Treatment Algorithms: Current stroke guidelines incorporate the presence of a dense artery sign as a factor supporting aggressive reperfusion strategies, especially when advanced imaging (CT angiography) is unavailable.
- Follow‑up Imaging: Repeat CT or perfusion imaging is performed to assess for reperfusion, infarct evolution, and hemorrhagic transformation.
Limitations
- The sign is not universally present in all cases of acute large‑vessel occlusion; a normal‑density artery does not exclude an occlusion.
- Inter‑observer variability can affect detection, particularly in subtle cases.
References (selected)
- Brinjikji W, et al. “The Hyperdense Middle Cerebral Artery Sign in Acute Ischemic Stroke: A Systematic Review and Meta‑Analysis.” Stroke 2020.
- Inoue M, et al. “CT Hyperdense Artery Sign: Clinical Significance and Correlation with CT Angiography Findings.” Neuroradiology 2018.
- American Heart Association/American Stroke Association. “2021 Guideline for the Early Management of Patients with Acute Ischemic Stroke.” Stroke 2021.
The dense artery sign remains an important early imaging marker in the evaluation of acute ischemic stroke, facilitating rapid diagnosis and therapeutic decision‑making.