Acute Subdural Hematoma
An acute subdural hematoma (aSDH) is a collection of blood in the space between the dura mater and the arachnoid membrane that accumulates within the first few days after injury. It usually develops after severe head trauma, is frequently accompanied by underlying brain injury, and may require prompt diagnosis and surgical treatment.
Last updated: 2026-06-07
Definition
A subdural hematoma is a collection of blood in the subdural space between the dura mater and the arachnoid membrane, classified by timing as acute (0-3 days), subacute (3-21 days) and chronic (more than 21 days). An acute subdural hematoma is the form that develops soon after severe head trauma. It commonly results from tearing of the bridging veins that connect the brain surface to the cortex, or from bleeding within an area of cortical contusion. It accounts for a substantial proportion of all traumatic intracranial hematomas.
Causes and Risk Factors
The most common mechanism is acceleration-deceleration injury; road traffic accidents, falls from height and direct impacts are typical. In older people with brain atrophy the bridging veins are stretched and fragile, so even relatively minor trauma can cause bleeding. Patients taking blood-thinning (anticoagulant) or anti-platelet medication carry a higher risk. An acute subdural hematoma is often accompanied by brain contusion, diffuse axonal injury and brain swelling.
Symptoms
Symptoms depend on the size of the bleed and the accompanying brain injury. They may include headache, confusion and progressively deepening impairment of consciousness, weakness on one side of the body, difficulty with speech and seizures. Large hematomas can rapidly cause midline shift and displacement of brain tissue (herniation); pupil dilation, weakness on the opposite side and loss of consciousness may then develop. Severe cases may present as an emergency.
Diagnosis
Brain CT is the first-line investigation. On CT an acute subdural hematoma typically appears as a crescent-shaped hyperdense collection following the convexity of the brain and, unlike an epidural hematoma, can cross suture lines. The midline shift is often more marked than the thickness of the hematoma, because accompanying edema and contusion add to the mass effect. In the subacute phase the hematoma may appear at the same density as the brain (isodense); indirect signs and, where needed, magnetic resonance imaging (MRI) then aid diagnosis.
Treatment Options
Acute subdural hematomas of significant thickness, causing midline shift or leading to neurological deterioration require urgent surgery. Through a craniotomy the dura is opened, the hematoma is evacuated and the sources of bleeding are controlled. If there is associated widespread brain swelling and a risk of herniation, a decompressive craniectomy (temporary removal of the bone flap) may be performed; the bone is later replaced by cranioplasty. In small, neurologically stable patients, close monitoring in intensive care, intracranial pressure management and follow-up CT may be appropriate. In patients on blood thinners, reversal of the drug's effect is an important part of treatment.
Course and Recovery
The course of an acute subdural hematoma is generally closely linked to the severity of the accompanying brain injury and can be more serious than that of a chronic subdural hematoma. Age, the level of consciousness on presentation (Glasgow Coma Scale) and hematoma size all influence the outcome. Results may be more favorable in patients who are relatively alert. Care is planned by a multidisciplinary team; outcomes vary from patient to patient and no result can be guaranteed.
References
- Greenberg MS. Greenberg's Handbook of Neurosurgery. 10th ed. Thieme; 2023:1076-1081.
- Bullock MR, Chesnut R, Ghajar J, et al. Surgical management of acute subdural hematomas. Neurosurgery. 2006;58(3 Suppl):S16-S24.
- Carney N, Totten AM, O'Reilly C, et al. Guidelines for the Management of Severe Traumatic Brain Injury. 4th ed. Neurosurgery. 2017;80(1):6-15.
This article is for general information and does not replace a medical examination. Diagnosis and treatment decisions are individual.