Summary of Neuroimaging of Intracranial Hematomas

## Introduction Intracranial hemorrhage encompasses various types of bleeding within the skull, which differ in location, mechanism of onset, and clinical outcomes. This material focuses on **subarachnoid hemorrhage (SAH)** and **intraventricular hemorrhage (IVH)**, their imaging features, complications, and practical approaches to diagnosis and monitoring. > **Definition:** Subarachnoid hemorrhage (SAH) is the presence of blood in the subarachnoid space, between the arachnoid mater and the pia mater. Intraventricular hemorrhage (IVH) refers to the entry of blood into the brain's ventricular system. ## Basic Classification and Mechanisms ### Subarachnoid Hemorrhage (SAH) - Most commonly arises from the rupture of small subarachnoid vessels following trauma, or from the extension of a contusion/hematoma into the subarachnoid space. - In patients found unconscious, SAH may signal an aneurysmal rupture rather than trauma; in such cases, CT angiography or conventional angiography should be considered. > **Definition:** Hyperacute SAH is an early stage of hemorrhage where the blood is fresh, and its MR signal can be difficult to detect. ### Intraventricular Hemorrhage (IVH) - Can arise through three main mechanisms: 1. Tearing of subependymal veins on the ventricular surface due to a rotational mechanism. 2. Direct extension of a parenchymal hematoma into the ventricles. 3. Retrograde flow of blood from the subarachnoid space through the foramina of the fourth ventricle into the ventricular system. ## Imaging: CT vs. MR ### CT (Computed Tomography) - SAH: Linear areas of high density in the cisterns and sulci. On the convexity or near the tentorium, it can spread into the sulci, which helps differentiate it from other collections. - IVH: Hyperdense material layered within the ventricular system; a small amount in the occipital horns can be the only clue. ### MR (Magnetic Resonance) - Hyperacute SAH may be isointense to brain parenchyma on conventional T1W and T2W sequences and thus harder to recognize. However: - **FLAIR** and **SWI** are more sensitive than CT for detecting acute subarachnoid hemorrhage. - Subacute SAH is often better visualized on MR due to its high signal intensity at a time when it may be isodense with CSF on CT. - Chronic hemorrhage can leave hemosiderin staining in the subarachnoid space, known as "superficial hemosiderosis," which appears as a marked signal drop on T1 and T2 sequences. > **Definition:** SWI (Susceptibility Weighted Imaging) is an MR sequence sensitive to the presence of blood products and hemosiderin, displaying hypointense areas. ## Clinical Implications and Complications - Both SAH and IVH can lead to subsequent hydrocephalus, either from impaired CSF absorption at the level of the arachnoid villi or from obstruction (e.g., in the aqueduct in cases of IVH). - Hydrocephalus can manifest acutely or with delayed onset and requires active monitoring and treatment (e.g., external ventricular drainage). ## Diagnostic Procedure and Practical Examples 1. For a patient who has sustained trauma with suspected hemorrhage: * Immediately perform a non-contrast head CT for rapid detection of hemorrhage (SAH, IVH) and assessment of any massive hematoma. 2. If CT findings are non-specific, or if there's suspicion of aneurysm rupture in cases of unclear trauma: * Supplement with CT angiography or conventional angiography. 3. If the CT is negative, but the clinical impression strongly suggests SAH (e.g., sudden headache, a constellation of neurological deficits): * MRI with FLAIR and SWI sequences can reveal acute or subacute SAH, especially if it involves smaller or spreading hemorrhage into the sulci. Practical example: A patient suddenly loses consciousness without known trauma, and a CT scan shows high-density lines in the cisterns. This leads us to suspect aneurysm rupture, and CT angiography is indicated. ## Comparison of SAH and IVH (Table) | Characteristi