Chronic Subdural Hematoma

Etiology

• SDH is a type of intracranial hemorrhage characterized by bleeding that occurs between the dural and arachnoid membranes that surround the brain.^1,2
• SDHs can be classified into several subtypes based on:²
  • Time course: acute, subacute, acute on chronic, and chronic
  • Etiology: traumatic, spontaneous, and other pathologies
  • Special considerations: anticoagulation-induced, bilateral, recurrent, etc.
• Chronic SDH can result from minor head trauma, especially in patients with age-related brain atrophy or on anticoagulation.²
• Lowering of intracranial pressures (ICP) can also lead to chronic SDH.
  • Decreased ICP may result from a cerebral spinal fluid (CSF) leak following lumbar puncture, ventriculostomy, shunt placement, or other neurosurgical procedure.¹
  • The decrease in ICP causes the brain to depress in the skull leading to engorgement and stretching of the bridging veins.²

Pathophysiology

• Minor trauma leads to damage of venous structures and a collection of small amounts of blood in the subdural space.
• Normal absorption of SDH is reliant upon counter pressure from brain tissue and the lack of potential subdural space.
  • The minor inciting events for chronic SDH typically cause little brain swelling.
  • The patients at risk for chronic SDH often have increased subdural space from aggressive shunting, atrophy, or alcoholism.²
• Continued bleeding may be due to the formation of neomembranes around the hematoma.²
  • Part of this membrane is highly vascularized and may lead to repeat bleeding.
  • Another part of the membrane secretes antithrombotic and fibrinolytic enzymes.

Clinical Presentation and Diagnosis

• Patients with chronic SDH are more likely to present with nonfocal symptoms such as headache, light-headedness, seizures, behavioral changes, cognitive impairment, somnolence, gait disturbances, memory problems, etc.^1-3
• Chronic SDH is as a reversible cause of dementia.³
• A noncontrast head computed tomography is often used to diagnose chronic SDH. It appears as a crescent-shaped mass, and is often more hypodense than an acute SDH.³

Treatment Options

• Like acute SDH, the treatment of chronic SDH includes:^1,2
  • Ensuring a patent airway, adequate oxygenation, and ventilation
  • Maintaining stable hemodynamics and avoiding hypo- or hypertension
  • Performing a detailed neurological examination to determine the severity of neurological deficits and provide a baseline to assess for clinical deterioration.
  • Avoiding elevations in ICP by raising the head of the bed and ensuring venous drainage
  • Reversing anticoagulation, if necessary
  • Administering seizure prophylaxis
  • Neurosurgical consultation for surgical decompression
• Surgical decompression is a treatment option for chronic SDH.
  • Most surgeons agree that many chronic SDHs require surgery because the body lacks the natural ability to reabsorb the blood.²
  • Surgery is commonly required due to the tendency of the bleeding to increase overtime.²
  • Indications for surgical evacuation include clot thickness greater than 10 mm or midline shift greater than 5 mm on brain scans.²
  • All symptomatic lesions should be considered for surgical management.²
• Multiple surgical techniques have been used for surgical evacuation and any of them can be augmented by the placement of a subdural drain.^1,2
  • Open craniotomy
  • Burr-hole craniotomy
  • Twist-drill craniostomy with drainage catheter, which can be performed at the bedside in the intensive care unit.
• Embolization of the middle meningeal artery (MMA)
  • MMA embolization may be used as adjunctive therapy to prevent recurrence after the mass effect is reduced⁴ (Figure 1).
  • MMA embolization reduces recurrence rates by preventing microbleeding episodes from immature neovessels of the membranes surrounding the chronic SDH.⁴