# Subacute and Chronic Subdural Hematoma Management

## Introduction

Chronic subdural hematoma is one of the most common neurosurgical conditions, particularly in the elderly population. It is defined as a subdural collection presenting more than 21 days after the inciting event, while subacute SDH presents between 3 and 21 days. The incidence is rising with aging populations and increasing anticoagulant use, reaching approximately 20 to 30 per 100,000 per year in patients over 70.

## Pathophysiology

The process begins with an initial bridging vein tear that creates a subdural blood collection. Organization of the hematoma leads to neomembrane formation from dural border cells. These neomembranes contain fragile, leaky capillaries that undergo repeated microhemorrhages. Inflammatory mediators including VEGF, IL-6, and IL-8 drive angiogenesis and membrane permeability. An osmotic gradient draws fluid into the collection, causing gradual enlargement. The result is a self-perpetuating cycle of membrane formation, microhemorrhage, and fluid accumulation. Risk factors include advanced age, cerebral atrophy, anticoagulation or antiplatelet therapy, alcoholism, coagulopathy, prior head trauma, and CSF shunting.

## Clinical Presentation

The onset is insidious, with headache, cognitive decline, confusion, and gait instability developing gradually. The condition may mimic dementia, stroke, or brain tumor. Fluctuating neurological symptoms with waxing and waning consciousness level are characteristic. Focal deficits include hemiparesis and speech difficulty when the dominant hemisphere is affected. Seizures occur in 5 to 10 percent. Bilateral cSDH is present in 15 to 25 percent of cases and may present with symmetric or misleading symptoms. A history of trauma may be absent or may be remote and trivial.

## Imaging

CT demonstrates a crescent-shaped extra-axial collection. Subacute collections at 3 to 21 days are isodense to brain parenchyma and can be missed on CT. Chronic collections beyond 21 days appear hypodense compared to brain. Mixed density suggests recurrent hemorrhage within a chronic collection. MRI is superior for detecting isodense collections and visualizing membranes. Maximum thickness and midline shift are measured, and evaluation for bilateral collections and underlying parenchymal pathology is important.

## Management Decision-Making

### Non-Operative Management

Non-operative management is appropriate for small collections under 10 millimeters with minimal midline shift in asymptomatic or minimally symptomatic patients. Serial CT imaging at 2 to 4 week intervals monitors for progression. Coagulopathy is corrected and anticoagulation held when safely possible. Corticosteroids with dexamethasone have emerging but uncertain evidence; the Dex-CSDH trial showed non-inferiority was not established and a higher complication rate. Middle meningeal artery embolization is increasingly used as primary or adjunctive treatment.

### Surgical Indications

Surgery is indicated for symptomatic patients with neurological deficits, significant headache, or cognitive decline. Additional indications include maximum thickness greater than 10 millimeters or midline shift greater than 5 millimeters, neurological deterioration during observation, and radiographic progression on serial imaging.

## Surgical Techniques

### Burr Hole Drainage

Burr hole drainage is the most common and preferred technique for uncomplicated chronic SDH. One or two burr holes are placed under local or general anesthesia. The dura and outer membrane are opened, and irrigation continues until the fluid runs clear. A subdural drain connected to a closed system is placed for 24 to 48 hours postoperatively. The Santarius trial demonstrated that subdural drain placement reduces recurrence from 24 percent to 9 percent.

### Twist Drill Craniostomy

This bedside procedure is performed under local anesthesia through a 3 to 5 millimeter twist drill hole. A catheter is placed into the subdural space connected to a closed drainage system. It is suitable for high-risk surgical patients. The recurrence rate is higher than burr hole drainage but procedural morbidity is lower.

### Craniotomy

Craniotomy is reserved for organized hematomas with thick membranes, multiloculated collections, or recurrent cSDH after failed burr hole drainage. It allows direct visualization and membrane excision. The complication rate is higher, and it is reserved for refractory cases.

### Middle Meningeal Artery Embolization

MMA embolization is an emerging technique that targets the blood supply to the neomembranes. It is performed via transfemoral catheterization with particle or liquid embolic agents. It can serve as primary treatment, adjunct to surgery, or treatment for recurrent cSDH. The EMBOLISE trial and other randomized controlled trials demonstrate significant reduction in recurrence and reoperation. Growing evidence supports MMA embolization as first-line or early adjunctive therapy.

| Technique | Anesthesia | Recurrence Rate | Best Indication |
|-----------|-----------|-----------------|-----------------|
| Burr hole drainage (± drain) | Local or general | 9-15% (with drain) | Uncomplicated cSDH (first-line) |
| Twist drill craniostomy | Local | Higher than burr hole | High surgical risk patients, bedside |
| Craniotomy | General | Lowest | Organized/multiloculated, recurrent after burr hole |
| MMA embolization | Local (sedation) | Significantly reduced | Adjunct to surgery, primary in select cases, recurrent cSDH |

## Postoperative Management

Flat bed rest for 24 to 48 hours promotes brain re-expansion, though practice varies. Gradual mobilization follows drain removal. Patients avoid Valsalva maneuvers, straining, and heavy lifting. The subdural drain is typically removed at 24 to 48 hours or when output falls below 50 milliliters per day. Serial CT imaging is obtained at 1 month and 3 months post-surgery. Residual collection is common and expected; clinical status rather than imaging appearance drives management decisions. Anticoagulation resumption is individualized, typically restarted at 1 to 4 weeks based on thromboembolic risk.

## Recurrence

Recurrence rates range from 5 to 30 percent depending on technique, drain use, and risk factors. Risk factors for recurrence include bilateral cSDH, coagulopathy or anticoagulation, diabetes, brain atrophy, no drain placement, and postoperative pneumocephalus. Management of recurrence includes repeat burr hole drainage, MMA embolization, and craniotomy for organized collections. Atorvastatin at 20 milligrams per day has some evidence for accelerating cSDH resolution in non-surgical or post-surgical patients.

## Anticoagulation and Antiplatelet Considerations

Warfarin is reversed with vitamin K, fresh frozen plasma, or prothrombin complex concentrate before surgery and held for 7 to 14 days postoperatively. DOACs are held for 24 to 48 hours preoperatively with specific reversal agents used if urgent surgery is needed. Aspirin may increase recurrence risk but is often continued if a strong cardiac indication exists. Resumption timing requires multidisciplinary discussion among neurosurgery, cardiology, and hematology.

## Clinical Pearls

Always consider bilateral chronic SDH in elderly patients presenting with symmetric or fluctuating neurological symptoms; isodense collections may be missed on CT alone and MRI should be considered. Subdural drain placement after burr hole evacuation is supported by Class I evidence from the Santarius randomized controlled trial and should be standard practice unless contraindicated. Middle meningeal artery embolization represents a paradigm shift in cSDH management, with growing evidence supporting its role in reducing recurrence as both primary and adjunctive therapy. Residual subdural collections on postoperative imaging are expected and should not prompt reoperation unless the patient is clinically symptomatic or deteriorating.

## References
1. Santarius T, Kirkpatrick PJ, Ganesan D, 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.
2. Hutchinson PJ, Edlmann E, Bulters D, et al. Trial of dexamethasone for chronic subdural hematoma (Dex-CSDH). N Engl J Med. 2020;383(27):2616-2627.
3. Fiorella D, Arthur AS, Grissenauer CJ. The EMBOLISE trial: middle meningeal artery embolization for chronic subdural hematoma. J Neurointerv Surg. 2024;16(1):25-30.
4. Kolias AG, Chari A, Santarius T, Hutchinson PJ. Chronic subdural haematoma: modern management and emerging therapies. Nat Rev Neurol. 2014;10(10):570-578.