MRI evolution of hemorrhage
Magnetic resonance imaging allows for a clear staging of hemorrhage. The appearance of a hematoma on scans directly depends on the form of hemoglobin—it is its diamagnetic and paramagnetic effects that generate the signal.
- Hyperacute stage (Hyperacute). Lasts up to several hours. At this point, oxyhemoglobin (oxy-Hb) predominates. On T1-weighted images, the lesion appears isointense or hypointense, and on T2/FLAIR, hyperintense relative to the parenchyma.
- Acute stage (Acute). Lasts up to one day (~24 hours). Oxyhemoglobin loses oxygen and converts into deoxyhemoglobin (deoxy-Hb). On T1, the signal remains isointense, while on T2/FLAIR it becomes hypointense.
- Early subacute stage (Early subacute). From one day to several days. Methemoglobin (met-Hb) accumulates inside erythrocytes. The T1 signal changes to hyperintense, while T2/FLAIR remains hypointense.
- Late subacute stage (Late subacute). From several days to several weeks. Erythrocyte lysis occurs, and methemoglobin becomes extracellular. Now the hematoma appears hyperintense on both T1 and T2/FLAIR.
- Chronic stage (Chronic). Occurs weeks or months later. A collection of hemosiderin (haemosiderin) forms. On all main sequences (T1 and T2/FLAIR), the lesion is hypointense.
Dynamics of intraparenchymal hematoma
The evolution of an intraparenchymal hemorrhage is clearly visible on serial scans. Unless the hematoma is in the hyperacute stage, it appears moderately hyperdense on non-contrast CT (overall, the density of an acute hemorrhage gradually decreases from the 1st to the 10th day).
On MRI, the structure of the hematoma is heterogeneous. For example, on T1WI, a hyperintense rim may be identified at the periphery (due to the presence of methemoglobin), while the center remains hypointense. On the FLAIR sequence, this same rim yields a mixed signal (hyper- and hypointense), indicating the presence of both extracellular and intracellular methemoglobin.
After approximately a week, the lesion on FLAIR becomes predominantly hyperintense, with extracellular methemoglobin predominating. After several months, the hyperintense component disappears, leaving only a hypointense collection of residual hemosiderin.
Extra-axial spaces and types of hematomas
Hemorrhages can be localized outside the brain tissue, in the so-called extra-axial spaces. Normally, there is only one physiological space—the subarachnoid space (Subarachnoid space), located between the arachnoid and pia mater. It is filled with cerebrospinal fluid and contains blood vessels.
The epidural and subdural spaces are potential spaces, meaning they only arise in pathology (e.g., trauma).
- Epidural hematoma (EDH). Blood accumulates between the inner table of the skull and the periosteal layer of the dura mater. Most commonly of arterial origin due to injury to the middle meningeal artery from a cranial vault fracture. On CT, it has a biconvex lens shape, is bounded by cranial sutures, but can cross dural reflections (falx cerebri, tentorium cerebelli). Clinical presentation often progresses rapidly.
- Subdural hematoma (SDH). Located between the inner layer of the dura mater and the arachnoid mater. Occurs when cortical bridging veins (bridging veins) are injured. Unlike EDH, it has a crescent shape on CT and is not bounded by sutures—blood flows freely along the convexital surface of the brain. Can occur even with mild trauma.
Briefly: answers to topical questions
How does the X-ray density of an intraparenchymal hematoma change over time on CT?
The X-ray density of an intraparenchymal hematoma on non-contrast CT gradually decreases over time. In the acute stage, the hemorrhage appears hyperdense. From the 1st to the 10th day, the density progressively decreases. After 6 weeks, an area of decreased X-ray density (hypodensity) involving the cortex and white matter is identified at the site of the hematoma in the brain parenchyma.
What are the types of extra-axial intracranial hemorrhages?
There are three main types of extra-axial intracranial hemorrhages occurring within their respective anatomical spaces:
- Subarachnoid space (Subarachnoid space) — an accumulation of blood between the arachnoid and pia mater.
- Epidural hematoma (Epidural Haemorrhage) — localized between the inner table of the skull and the outer layer of the dura mater, with a biconvex shape.
- Subdural hematoma (Subdural Haemorrhage) — located in the potential space between the inner layer of the dura mater and the arachnoid mater, with a crescent shape.
What are the imaging findings of a subarachnoid hemorrhage on CT and MRI?
The imaging findings of a subarachnoid hemorrhage depend on the stage and imaging modality. On CT in the acute stage, the basal cisterns are filled with high-density blood, causing the external CSF spaces to appear bright. Blood may diffusely fill the cisterns or be localized asymmetrically. Concomitant dilatation of the temporal horns of the lateral ventricles is often observed. On MRI in the chronic stage, findings of superficial siderosis with hemosiderin deposition in the meninges are revealed. These deposits are best visualized on T2* GRE or SWI sequences.
What are the MRI findings of an intraventricular hemorrhage?
The MRI findings of an intraventricular hemorrhage directly depend on the age of the pathological process. The signal intensity of magnetic resonance changes during hematoma evolution as follows:
- Subacute stage — characterized by a high signal on tomograms.
- Chronic stage — characterized by a signal void (signal void).
Additionally, complications may be visualized on scans: extensive intraventricular hemorrhages are often accompanied by signs of post-hemorrhagic hydrocephalus.
Class and exam questions
How to tell on CT that an epidural hematoma is actively bleeding?
On non-contrast CT, look for hypodense areas within the hyperdense hematoma. Their presence indicates active bleeding and expansion of the lesion, requiring urgent neurosurgical intervention.
Why is an epidural hematoma bounded by cranial sutures while a subdural hematoma is not?
Epidural hematoma is bounded due to the tight adhesion of the periosteal layer of the dura mater to the cranial bones at the sutures. Subdural hematoma is located beneath the dura mater, where there are no anatomical barriers in the form of sutures.
What does the presence of gas bubbles in an epidural hematoma indicate?
Gas bubbles within the hematoma structure indicate a possible fracture of air-containing structures, such as the mastoid process or paranasal sinuses.
What else to study on this topic
- Venous epidural hematoma and dural sinus involvement
- Scalp tissue layers: from skin to the glial membrane of the cortex
- Anatomy of dural reflections: falx cerebri and tentorium cerebelli
- Features of detecting small subdural hemorrhages using multiplanar reconstructions
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