Subdural haemorrhage

A subdural haematoma is a collection of blood deep to the dural layer of the meninges. The blood is not within the substance of the brain and is therefore called an 'extra-axial' or 'extrinsic' lesion. They can be unilateral or bilateral.

• Acute: Symptoms usually develop within 48 hours of injury, characterised by rapid neurological deterioration
• Subacute: Symptoms manifest within days to weeks post-injury, with a more gradual progression.
• Chronic: Common in the elderly, developing over weeks to months. Patients may not recall a specific head injury.

The typical presentation of a subdural haematoma (SDH) often involves a history of head trauma, which may range from minor to severe. Patients frequently exhibit a lucid interval followed by a gradual decline in consciousness. This pattern is particularly common in chronic SDH. Other hallmark features include headache, confusion, and lethargy.

Clinical Features

• Altered Mental Status: Ranging from mild confusion to deep coma. Fluctuations in the level of consciousness are common.
• Focal Neurological Deficits: Weakness on one side of the body, aphasia, or visual field defects, depending on the haematoma's location.
• Headache: Often localised to one side, worsening over time.
• Seizures: May occur, particularly in acute or expanding hematomas.

• Papilloedema: Indicates raised intracranial pressure.
• Pupil Changes: Unilateral dilated pupil, especially on the side of the haematoma, indicating compression of the third cranial nerve.
• Gait Abnormalities: Including ataxia or weakness in one leg.
• Hemiparesis or Hemiplegia: Reflecting the mass effect and midline shift.

• Memory Loss: Especially in chronic SDH.
• Personality Changes: Irritability, apathy, or depression.
• Cognitive Impairment: Difficulty with attention, problem-solving, and other executive functions.

• Nausea and Vomiting: Secondary to increased intracranial pressure.
• Drowsiness: Progressing to stupor and coma in severe cases.
• Signs of Increased Intracranial Pressure: Such as bradycardia, hypertension, and respiratory irregularities (Cushing's triad).

Although the collection of blood is within the same anatomical compartment, acute and chronic subdurals have important differences in terms of their mechanisms, associated clinical features and management:

Acute subdural haematoma

An acute subdural haematoma is a collection of fresh blood within the subdural space and is most commonly caused by high-impact trauma. Since it is associated with high-impact injuries, there is often other brain underlying brain injuries.

There is a spectrum of severity of symptoms and presentation depending on the size of the compressive acute subdural haematoma and the associated injuries. Presentation ranges from an incidental finding in trauma to severe coma and coning due to herniation.

CT imaging is the first-line investigation and will show a crescentic collection, not limited by suture lines. They will appear hyperdense (bright) in comparison to the brain. Large acute subdural haematomas will push on the brain ('mass effect') and cause midline shift or herniation.

Small or incidental acute subdurals can be observed conservatively. Surgical options include monitoring of intracranial pressure and decompressive craniectomy.

Chronic subdural haematoma

A chronic subdural haematoma is a collection of blood within the subdural space that has been present for weeks to months.

Rupture of the small bridging veins within the subdural space rupture and cause slow bleeding. Elderly and alcoholic patients are particularly at risk of subdural haematomas since they have brain atrophy and therefore fragile or taut bridging veins.

Presentation is typically a several week to month progressive history of either confusion, reduced consciousness or neurological deficit.

Infants also have fragile bridging veins and can rupture in shaken baby syndrome.

On CT imaging they similarly are crescentic in shape, not restricted by suture lines and compress the brain ('mass effect'). In contrast to acute subdurals, chronic subdurals are hypodense (dark) compared to the substance of the brain.

If the chronic subdural is an incidental finding or if it is small in size with no associated neurological deficit then it can be managed conservatively with the hope that it will dissolve with time. If the patient is confused, has an associated neurological deficit or has severe imaging findings then surgical decompression with burr holes is required.