Surgical Intervention for Subdural Hematoma

Subdural hematoma (SDH) remains one of the most common neurosurgical emergencies, with management dictated by acuity, clot characteristics, neurological status, and patient comorbidities. Acute SDH (aSDH) carries a mortality rate of 40–60% in severe cases, while chronic SDH (cSDH) is increasingly prevalent in aging populations on anticoagulation. Surgical options range from emergent craniotomy for life-threatening aSDH to bedside twist drill craniostomy for stable cSDH. The landmark Santarius trial (2009) established that post-operative subdural drain placement significantly reduces cSDH recurrence — a finding that has become standard of care worldwide. Understanding the indications, timing, and technique for each SDH subtype is essential for neurologists involved in acute neurosurgical decision-making.

1. Classification and Epidemiology

SDH is classified by acuity based on timing from the inciting event, which correlates with clot characteristics and surgical approach:

Acute SDH is most commonly traumatic, occurring in approximately 10–20% of patients with severe traumatic brain injury (TBI). The mechanism involves tearing of parasagittal bridging veins or cortical vessel laceration. Non-traumatic causes include anticoagulant use (increasingly common with DOAC prescribing), coagulopathy, and rarely, spontaneous rupture of cortical arteries.

Chronic SDH has an incidence of approximately 5 per 100,000 population, rising to 58 per 100,000 in those aged ≥70 years. Brain atrophy with aging stretches bridging veins, lowering the threshold for rupture — often from trivial or forgotten trauma. The prevalence is projected to continue rising as the population ages and anticoagulant use expands.

2. Acute SDH: Surgical Indications

2.1 Brain Trauma Foundation Guidelines

The Brain Trauma Foundation (BTF) provides the most widely referenced surgical indications for aSDH. Surgery is recommended when any of the following criteria are met:

• Clot thickness >10 mm on CT imaging
• Midline shift >5 mm regardless of neurological status
• GCS decrease ≥2 points from the time of injury to hospital admission
• ICP >20 mmHg in a patient with GCS <9

Patients who do not meet surgical criteria should be monitored with ICP monitoring if GCS <9, with repeat CT within 6–8 hours or sooner if neurological status changes.

2.2 Factors Influencing Surgical Decision-Making

Beyond the BTF criteria, several additional factors guide the decision to operate:

• Patient age: Age >65 years is the strongest predictor of poor outcome. However, age alone should not preclude surgery in a patient with a favorable neurological exam.
• GCS at presentation: GCS <9 is associated with mortality rates exceeding 60%. Combined with age >65, this group has the highest predicted mortality.
• Pupillary response: Fixed, dilated pupils (bilateral) carry >90% mortality; unilateral fixed pupil carries approximately 50–60% mortality but can improve with rapid surgical decompression.
• Anticoagulation status: Active anticoagulation necessitates immediate reversal before surgery; the additional time required for reversal must be weighed against the urgency of evacuation.
• Comorbidities and goals of care: Pre-injury functional status, advance directives, and family discussions are essential components of surgical decision-making, particularly in elderly patients with severe presentations.

3. Acute SDH: Surgical Techniques

3.1 Craniotomy

Craniotomy is the standard surgical approach for acute SDH with significant mass effect. A large frontoparietal or frontotemporoparietal trauma craniotomy flap provides wide exposure for clot evacuation, identification of bleeding sources, and hemostasis. Key technical considerations include:

• Generous bone flap extending from the frontal to parietal region, centered over the maximal clot thickness
• Cruciate dural opening to expose the entire clot
• Gentle irrigation and suction to remove the acute clot without damaging underlying cortex
• Meticulous hemostasis of the bridging vein stump and any cortical bleeding sources
• Bone flap replacement at the end of the procedure unless significant brain swelling precludes it

3.2 Decompressive Craniectomy

When significant brain swelling is anticipated or encountered intraoperatively, the bone flap is not replaced. Decompressive craniectomy (DC) is considered when:

• Intraoperative brain swelling prevents safe bone flap replacement
• Preoperative imaging suggests diffuse brain edema (effaced cisterns, bilateral injury)
• Severe TBI with expected secondary swelling (young patients with high-energy mechanisms)
• The RESCUE-ICP paradigm: DC may serve as a last-tier therapy for refractory intracranial hypertension

The RESCUE-ICP trial (2016) demonstrated that DC for refractory ICP elevation in TBI reduced mortality (26.9% vs. 48.9%) but increased severe disability, with an overall shift toward better outcomes on ordinal mRS analysis at 12 months. Families must understand the trade-off between survival and potential severe disability.

3.3 Burr Hole Drainage for Liquefied Acute SDH

Occasionally, an acute SDH that has partially liquefied (typically in the transition to subacute phase) can be evacuated via burr holes. This is appropriate only when the collection is predominantly fluid and the patient is not deteriorating rapidly. In most true acute SDH, the solid clot requires open craniotomy for adequate evacuation.

4. Timing of Surgery for Acute SDH

Time to surgery is one of the most critical modifiable factors in aSDH outcomes. Multiple observational studies have consistently demonstrated that earlier surgery is associated with reduced mortality:

• Ultra-early surgery (<4 hours): Associated with mortality rates of 30–40%, compared with >60% when surgery is delayed beyond 4 hours in patients with severe aSDH (GCS ≤8).
• Independent predictor: Time from injury to operating room is an independent predictor of mortality, even after adjusting for age, GCS, and pupillary status.
• The "golden 4 hours": Large retrospective analyses demonstrate a step-wise increase in mortality with each hour of surgical delay.

5. Acute SDH: Outcomes and Prognostic Factors

Despite surgical intervention, outcomes for severe aSDH remain poor. Published mortality rates range from 40–60%, with favorable functional outcome (GOS 4–5) achieved in only 20–40% of operated patients. The strongest predictors of outcome include:

Prognostic discussions with families should incorporate these factors while acknowledging the significant uncertainty in individual predictions. The IMPACT and CRASH prognostic calculators, originally developed for TBI, can provide some guidance but were not specifically designed for isolated aSDH.

6. Chronic SDH: Surgical Techniques

6.1 Burr Hole Drainage

Burr hole drainage is the most widely used and recommended first-line surgical technique for symptomatic cSDH. The procedure involves:

• One or two burr holes placed over the maximal collection, typically one frontal and one parietal
• Dural opening and evacuation of the liquefied chronic collection
• Copious irrigation with warm saline until effluent is clear
• Placement of a closed subdural drainage system (see Section 7)

The procedure can be performed under general or local anesthesia, takes approximately 30–60 minutes, and carries a complication rate of approximately 5–10% (including acute SDH, seizures, pneumocephalus, and infection).

6.2 Twist Drill Craniostomy

Twist drill craniostomy (TDC) is a minimally invasive bedside alternative using a smaller (5 mm) drill hole. A catheter is placed into the subdural space and connected to a closed drainage system. Advantages include:

• Can be performed at the bedside under local anesthesia
• Shorter procedure time (<15 minutes)
• Suitable for high surgical risk patients or those on anticoagulation where formal surgery carries increased risk

Systematic reviews and meta-analyses comparing TDC with burr hole drainage suggest comparable recurrence rates and outcomes, though the evidence is predominantly observational. TDC is less effective for organizing collections with thick membranes.

6.3 Craniotomy for Chronic SDH

Craniotomy is reserved for specific cSDH scenarios:

• Organized or septated collections that cannot be adequately evacuated through burr holes
• Calcified or ossified cSDH (rare) requiring direct membrane excision
• Recurrent cSDH after failed burr hole drainage (particularly with thick neomembranes)
• Mixed-density collections with solid components not amenable to drainage

7. Post-Operative Subdural Drain: The Santarius Trial

The placement of a post-operative subdural drain following burr hole evacuation of cSDH was definitively addressed by the landmark Santarius trial (2009, Lancet). This single-center RCT enrolled 269 patients undergoing burr hole drainage for cSDH and randomized them to subdural drain placement for 48 hours vs. no drain.

Key Results

• Recurrence at 6 months: 9.3% with drain vs. 24.0% without drain (p = 0.003)
• Number needed to treat (NNT): 7 — one of the most favorable NNTs in neurosurgery
• Reoperation rate: Significantly lower with drain (1.6% vs. 9.8%)
• Mortality at 6 months: 8.6% with drain vs. 18.1% without drain (p = 0.042)
• Complications: No significant increase in drain-related complications (empyema, hemorrhage)

This trial established subdural drain placement after burr hole drainage as standard of care. The drain is typically maintained for 24–48 hours with the patient in a flat or slight Trendelenburg position to promote brain re-expansion and drainage.

8. Subacute SDH

Subacute SDH (3–21 days from injury) occupies a transitional zone between acute and chronic subtypes, with variable clot consistency that influences surgical approach:

• Early subacute (3–7 days): Clot is often partially liquefied but may retain solid components. Craniotomy may be necessary if the collection has significant solid elements.
• Late subacute (7–21 days): Collections are typically more liquefied and may be amenable to burr hole drainage.
• Imaging challenge: Isodense appearance on CT may lead to missed diagnosis. MRI or CT with contrast can improve detection.
• Surgical planning: Pre-operative imaging should assess clot consistency (presence of membranes, septations, mixed densities) to guide the choice between burr hole and craniotomy.

9. Anticoagulation Reversal Prior to Surgery

Patients on anticoagulation require immediate reversal before any surgical intervention for SDH. The choice of reversal agent depends on the anticoagulant:

10. Post-Operative Management

10.1 Immediate Post-Operative Care

• Positioning: Flat bed rest (or slight Trendelenburg) for 24–48 hours to promote brain re-expansion and subdural space obliteration
• Subdural drain management: Maintain closed drainage system at the level of the external auditory meatus; remove after 24–48 hours
• Avoid Valsalva maneuvers: Cough suppression, stool softeners, and adequate pain control to prevent strain
• Hydration: Liberal IV fluids to promote brain re-expansion
• Seizure prophylaxis: Levetiracetam or phenytoin for 7 days post-operatively (particularly after aSDH with cortical injury)

10.2 Serial Imaging

• Post-operative CT within 24 hours to assess evacuation completeness and identify complications (acute hemorrhage, pneumocephalus)
• Subsequent imaging at 2–4 weeks, then monthly until resolution
• Expect a small residual collection in most post-operative cSDH patients — this typically resolves over weeks as the brain re-expands
• Progressive pneumocephalus or failure to re-expand may indicate a CSF leak or trapped air requiring intervention

10.3 Restarting Anticoagulation

The decision to restart anticoagulation after SDH requires careful balancing of recurrence risk against thromboembolic risk:

• Mechanical heart valves and recent VTE: Higher urgency to restart; generally considered at 1–2 weeks if imaging is stable
• Atrial fibrillation: Can typically wait 2–4 weeks; use CHA₂DS₂-VASc to quantify stroke risk
• Shared decision-making: Involve neurosurgery, neurology, and cardiology in the decision
• DOACs vs. warfarin: Observational data suggest DOACs are associated with lower SDH recurrence rates compared with warfarin after restarting anticoagulation
• Serial imaging: Confirm stability of the collection before restarting; consider repeating CT at 1–2 weeks

11. Recurrence After Chronic SDH Surgery

Recurrence is the most common complication after cSDH surgery, occurring in 10–20% of cases. Risk factors for recurrence include:

• Bilateral cSDH: Higher recurrence on each side, especially if only one side is initially drained
• Thick neomembranes: Highly vascularized membranes continue to bleed after drainage
• Ongoing anticoagulation: Particularly warfarin; patients unable to discontinue anticoagulation have the highest recurrence rates
• Coagulopathy: Liver disease, thrombocytopenia, and other bleeding diatheses
• Diabetes mellitus: Associated with impaired membrane resorption
• Brain atrophy: Limits brain re-expansion after drainage, leaving dead space for reaccumulation
• No subdural drain: The Santarius trial demonstrated a 2.5-fold increase in recurrence without drain placement

Management of recurrent cSDH includes repeat burr hole drainage, consideration of craniotomy for organized collections, and increasingly, middle meningeal artery (MMA) embolization as an adjunctive or standalone treatment.

12. Surgical Technique Comparison

References

1. Bullock MR, et al. Surgical management of acute subdural hematomas. Neurosurgery. 2006;58(3 Suppl):S16–S24.
2. Santarius T, et al. Use of drains versus no drains after burr-hole evacuation of chronic subdural haematoma: a randomised controlled trial. Lancet. 2009;374(9695):1067–1073.
3. Hutchinson PJ, et al. Trial of decompressive craniectomy for traumatic intracranial hypertension (RESCUEicp). N Engl J Med. 2016;375(12):1119–1130.
4. Kolias AG, et al. Chronic subdural haematoma: modern evidence for comprehensive management. Lancet. 2014;384(9936):2166–2176.
5. Lega BC, et al. Choosing the best operation for chronic subdural hematoma: a decision analysis. J Neurosurg. 2014;121(5):1085–1091.
6. Almenawer SA, et al. Chronic subdural hematoma management: a systematic review and meta-analysis of 34,829 patients. Ann Surg. 2014;259(3):449–457.
7. Seelig JM, et al. Traumatic acute subdural hematoma: major mortality reduction in comatose patients treated within four hours. N Engl J Med. 1981;304(25):1511–1518.
8. Wilberger JE Jr, et al. Acute subdural hematoma: morbidity, mortality, and operative timing. J Neurosurg. 1991;74(2):212–218.
9. Greenberg SM, et al. 2022 Guideline for the Management of Patients With Spontaneous Intracerebral Hemorrhage. Stroke. 2022;53(7):e282–e361.
10. Connolly SJ, et al. Andexanet alfa for factor Xa inhibitor-associated acute intracranial hemorrhage (ANNEXA-I). N Engl J Med. 2024;390(19):1745–1755.
11. Carney N, et al. Guidelines for the Management of Severe Traumatic Brain Injury, 4th Edition. Neurosurgery. 2017;80(1):6–15.
12. Soleman J, et al. Evidence-based treatment of chronic subdural hematoma. In: Textbook of Neurointensive Care. Springer; 2023.