2 Chronic Subdural Hematomas

Introduction

Chronic subdural hematoma (CSDH) is one of the most commonly treated neurosurgical disorders in the world. The 2006 American Association of Neurological Surgeons procedural survey reported over 43,000 bur holes performed for the evacuation of extra-axial (subdural/epidural) hematomas. ¹ The most common patient characteristics are elderly males with or without a history of head trauma. ² ^, ³ Additional risk factors include a history of alcoholism, the presence of an internal cerebrospinal fluid (CSF) shunt, and acquired or congenital bleeding diathesis. ⁴ CSDHs are often unilateral, but present as bilateral in approximately 16 to 25% of cases. ³ ^, ⁵ The most common presenting symptoms include headache, ataxic gait, confusion, aphasia, and various nonspecific complaints. If the CSDH is large and causes significant mass effect, paresis, seizure, and coma may ensue. Mortality statistics vary among institutions, but generally range from 5 to 16%. ⁶ ^, ⁷

Several theories exist to explain the pathogenesis of CSDH. The prevailing hypothesis is that most start as acute subdural bleeds that trigger a local inflammatory response in the surrounding meninges. Inflammation triggers the migration of fibroblasts, which then create membranes that organize the clot and secrete vascular endothelial growth factor (VEGF) that, in turn, promotes the formation of capillaries within these membranes. ⁸ Over time, these membrane capillaries bleed and prevent the blood from being reabsorbed. Hemoglobin eventually is broken down into hemosiderin, leading to the characteristic appearance of CSDH on computed tomography (CT)/magnetic resonance (MR) imaging ( Fig. 2.1 ).

Management of CSDH typically involves surgical evacuation of the clot and placement of postsurgical drains to prevent reaccumulation of blood in the subdural space. In particular, the use of drains after bur hole evacuation of CSDH has been shown to reduce both recurrence and mortality at 6 months. ⁹ Several operative approaches are available. Bur hole drainage is performed most commonly. A “mini”-craniotomy may augment visualization of the subdural space. When the radiographic appearance is favorable, bedside procedures—such as minimally invasive twist drill catheter placement or suction evacuation—can be used to good effect. In addition to these surgical techniques, several small studies have suggested that dexamethasone therapy might show some promise in treating CSDH. ¹⁰ ^, ¹¹ Newer pharmacological treatment, such as the use of tranexamic acid (an antithrombolytic agent), is investigational. ¹² CSDH recurrence rates vary among institutions, but generally range from 8 to 16%. ¹³ ^, ¹⁴ Several studies have suggested that CSDH recurrence rates are higher with bilateral CSDH, with large volumes of pneumocephalus after evacuation, and with use of anticoagulation therapy. ¹³ ^, ¹⁴

Indications

All Procedures

Subacute or chronic subdural hematoma with maximum thickness. 10 mm and/or midline shift. 7 mm
Subacute or chronic subdural of any thickness causing mass effect, midline shift, or neurologic signs and symptoms.

Minimally Invasive

Favorable CT imaging characteristics—a uniformly isodense or hypodense collection in the subdural space—are present. This suggests the subdural hematoma is sufficiently liquefied to permit drainage via a ventriculostomy catheter.
The presence of an isodense, or even slightly hyperdense, “ground glass” appearance is not necessarily a contraindication to catheter drainage. This phenomenon is seen sometimes in the setting of a subacute or “acute on chronic” subdural hematoma, often with a gradual gradient from anterior hypodensity to posterior hyperdensity (reflecting dependent acute blood mixed with the predominantly chronic hematoma). These usually can be drained effectively with a bedside catheter or suction evacuation procedure.
A small amount of acute, hyperdense subdural blood within a larger, mostly chronic, hypodense collection is not necessarily a contraindication.
While adequate drainage can be achieved even in the presence of a few subdural membranes, extensive membranes and multiple layers of subdural hematoma (SDH) of different ages or densities may pose a challenge. Bur hole drainage or craniotomy should be considered in this setting.

Preprocedure Considerations

Radiographic Imaging (Figs. 2.1, 2.2, and 2.3)

X-ray: In general, X-ray is a poor diagnostic tool for CSDH. Occasionally, a plain film of the skull may reveal a calcified CSDH. ¹⁵
CT: CT is the gold-standard imaging modality for diagnosing CSDH. SDHs classically demonstrate a crescentic configuration, as their distribution over the cortical convexity is not bounded by suture lines (in contrast to epidural bleeds). Mass effect, cortical buckling, and midline shift may also appear depending on the thickness and size of the clot. The appearance of blood on CT scan will change over time as the blood products age ( Table 2.1 ); subacute blood appears isodense and chronic blood, hypodense relative to brain. The degree of midline shift and thickness of subdural blood are useful radiographic markers to assist clinical decision making regarding operative intervention. Noncontrast CT usually is adequate to assess the age of the blood present, and therefore, the likelihood that it will be drained successfully via minimally invasive or open means. Contrast-enhanced imaging should be considered if there is concern for subdural empyema or for clarity in the setting of a subacute subdural hematoma that is isodense with respect to the brain tissue. Enhancement of cortical veins helps to define the boundary between cortex and hematoma. Contrast may also demonstrate the presence of membranes.
MRI: Magnetic resonance imaging (MRI) is similarly sensitive and specific for diagnosing CSDH as CT scan; it is potentially more sensitive in determining size and internal structure. ¹⁶ CT generally is preferred due to the high cost of MR imaging as well as the time required to perform the study. Similarly to CT scanning, the appearance of subdural blood will also change over time ( Table 2.2 ). MRI may be considered for more detailed evaluation of membranes and layers if there is concern regarding the feasibility of catheter drainage.

**Fig. 2.1** Patient with subacute subdural hematoma with a so-called “hematocrit” effect with blood of different densities layering in a dependent fashion. There is mass effect causing mild shift and left ventricular effacement. This patient was deemed a good candidate for bur hole drainage.

**Table 2.1** **CT appearance of subdural blood over time ¹⁷**
Time	Appearance relative to brain parenchyma
Hyperacute (< 24 hours) Acute (1–2 days) Subacute (2–13 days) Chronic (> 14 days)	Hypo-/isodense Hyperdense Isodense Hypodense

**Table 2.2** **MR appearance of subdural blood over time ¹⁸**
Time	T1	T2
Hyperacute (< 24 hours)	Hypo-/isointense	Hyperintense
Acute (1–3 days)	Hypo-/isointense	Hypointense
Early subacute (3–7 days)	Hyperintense	Hypointense
Late subacute (8–13 days)	Hyperintense	Hyperintense
Chronic (> 14 days)	Hypointense	Hyptointense

Medications

Intravenous (IV) antibiotics should be given within 1 hour prior to incision. The use of prophylaxis in the setting of minimally invasive bedside procedures is left to the discretion of the surgeon.
Antiepileptic drug prophylaxis should be administered.
Sedation for bedside procedures should be administered with caution. Minimize dosing or avoid sedation, if possible, as patients with CSDH may be particularly sensitive to its effects. One of the benefits of the bedside SDH drainage procedure is the possibility to witness rapid neurologic improvement when minimal or no sedating medications are used. This stands in contrast to the delayed emergence some (often elderly) patients experience after bur hole drainage under general anesthesia. Bur hole procedures in the operating room can be performed under conscious sedation or general anesthesia as per surgeon preference or patient tolerance. Craniotomies typically are performed under general anesthesia.

**Fig. 2.2a, b** Large right frontoparietal subdural hematoma causing mass effect and right ventricular effacement. There are some septations within the mixed density subdural. A small craniotomy was chosen to evacuate the collection.

**Fig. 2.3** CT scan of a patient′s head with a homogenous right hemispheric subdural hematoma and right to left midline shift. This case was selected for twist drill craniostomy.

Operative Field Preparation

The hair overlying the affected hemisphere is clipped with electric clippers.
Sterile skin preparation is performed with povidone iodine or chlorhexidine.
The planned incision sites are infiltrated with 1% lidocaine with 1:100,000 epinephrine.
Available imaging should be studied carefully to determine the ideal entry point for the twist drill craniostomy. The target is almost always more lateral than the typical insertion site for a ventriculostomy or intracranial pressure (ICP) monitor.

Operative Procedure

Bur Hole Drainage

Positioning and Skin Incision (Fig. 2.4a, b)

**Figure** Fig. 2.4 **Procedural Steps** The patient is positioned supine on a donut or a horseshoe, with the head rotated approximately 30 degrees to the contralateral side. A shoulder roll is placed longitudinally beneath the ipsilateral shoulder. The back of the bed is elevated slightly. **Bur Holes (Right)** Two incisions—each approximately 3 cm in length—are planned along a line that bisects the interval between midline and superior temporal line. The anterior incision is positioned just anterior to coronal suture and the posterior incision, over the parietal eminence. **Small Craniotomy (Left)** A “lazy ‘S’” incision is begun from approximately 1 cm below the superior temporal line extending superiorly approximately 2 cm lateral to the midline in the parietal region approximately 1 cm posterior to the coronal suture. The incision can be further tailored to the location and size of the hematoma. **Pearls** • For bilateral procedures, the head is kept in a neutral position. • Trace out a reverse question mark–type incision over the affected hemisphere. This will facilitate a more extensive opening, if necessary. The planned bur hole incision sites should fall along the superior limb of the question mark. • If the CT appearance of the extra-axial fluid is both hypodense and homogeneous, it may be possible to drain the collection through a single bur hole.

Incisions and Bur Holes/Craniotomy (Fig. 2.5)

**Figure** Fig. 2.5 **Procedural Steps** A no. 10 blade is used to open each incision to the level of pericranium. The pericranium is opened with Bovie electrocautery and swept to either side with a periosteal elevator. For the craniotomy, scalp clips are applied to the scalp edges. The temporalis is incised and is reflected with the skin incision. Self-retaining retractors are placed. **Bur Holes (Right)** **Place a single bur hole at each incision site, using a round or matchstick bur, perforator, or acorn drill. Apply bone wax to the bony edges as necessary.** **Small Craniotomy (Left)** • Place bur holes at the apices of the exposed calvarium. A footplate attachment, dental tool, or Penfield no. 3 is used to free the underlying dura from the bone. Use the craniotome to create a small bone flap, limited to the size of the opening. • The craniotome is used to create a roughly ovoid flap. The bone is elevated—using a blunt surgical tool to dissect any remaining dural attachments to the undersurface of the bone—and set aside in antibiotic solution. **Pearls** **• Bur Holes** ○ Bur holes should be 1.5 to 2 cm in diameter. • **Craniotomy** ○ Resistance may be encountered at the level of coronal suture, where the dura is more firmly adherent to bone. ○ The bone flap will be 4 to 5 cm in diameter.

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2 Chronic Subdural Hematomas