Chapter 23 Operative Exposure in Cranial Trauma: Damage Control Surgical Techniques

This chapter will discuss techniques for damage control during cranial trauma. The major emphasis of this lab experience is on indications, as well as technique for intracranial pressure (ICP) monitoring and decompressive hemicraniectomy (DHC).

Learning Objectives

By the end of this ASSET course module, participants should be able to do the following:

1. Understand the anatomical layers of the scalp, as well as its blood supply.
2. Describe the indications for intracranial pressure (ICP) monitoring.
3. Demonstrate proper placement of ICP monitors.
4. Describe the indications for decompressive hemicraniectomy (DHC).
5. Demonstrate proper surgical technique for DHC.

Considerations

• It must be kept in mind that the standard of care for treatment of severe traumatic brain injury includes direct evaluation and treatment by a trained neurosurgeon. This course module is not designed to replace care by a qualified neurosurgeon.
• The intent of this module is to outline basic, potentially lifesaving damage control neurosurgical skills that providers might employ in military, humanitarian, or rural settings when timely (more than four hours) specialist care is not available.
• If feasible, communication with a neurosurgeon is advised.

Anatomy

• The scalp has five anatomical layers (Figure 1) that can be remembered by the mnemonic SCALP, with structures progressing from superficial to deep, as follows:
  • Skin
  • Cutaneous tissue (dense)
  • Aponeurosis (galea)
  • Loose areolar tissue (AT)
  • Pericranium
• The scalp has a rich vascular supply from branches of the external carotid artery, with the main blood supply coming from the superficial temporal, posterior auricular, and occipital arteries.
• Bleeding from the scalp can be extensive and must be considered in the setting of unexplained hypotension.
• The brain is drained by superficial cortical “bridging” veins into larger dural venous sinuses. The main sinuses are the superior sagittal sinus and the transverse sinuses (Figure 1). Injury to these sinuses must be avoided during any cranial intervention.
• If injury to the dural venous sinus is present, operative intervention can result in catastrophic blood loss and should not be attempted without experience.
• The main muscle encountered is the temporalis muscle, which runs from the superior temporal line to the coronoid process of the mandible.

Pathophysiology

• Damage control neurosurgical techniques are most commonly required in the setting of traumatic head injury in which there is hemorrhage within the skull or brain swelling resulting in increased ICP and concern for brain herniation.
• Epidural and subdural hematomas are common indications for emergent neurosurgical intervention.

Epidural Hematoma

• An epidural hematoma is most commonly caused from a blow to the temporal skull and disruption of the middle meningeal artery (Figure 2).
• The hematoma forms between the inner table of the skull and the dural membrane.
• The classic finding on CT scan is of a convex, lens-shaped hematoma (Figure 2).
• The classic presentation of an epidural hematoma is a lucid interval following head trauma with rapid deterioration of Glasgow Coma Scale (GCS) as the hematoma expands and causes compression of the brain, with resultant herniation if not promptly relieved.

Subdural Hematoma

• Subdural hematomas result from the disruption of bridging veins where they penetrate the dura, leading to accumulation of blood between the dura and the subarachnoid covering of the brain (Figure 3).
• The classic finding on CT scan for a subdural hematoma is a crescent-shaped, concave hyperdensity (hematoma) (Figure 3).
• Subdural hematomas can be chronic or acute and can be associated with brain compression and eventual herniation if large and untreated.

Intracranial Pressure (ICP) Monitoring

Considerations

• ICP monitoring should be considered for patients with severe traumatic brain injury (post-resuscitation GCS < 8).
• There are two types of ICP monitors:
  • External ventricular drain (EVD)—Placed in frontal horn of lateral ventricle
  • Parenchymal monitors (bolt)—Placed a few centimeters into brain parenchyma
• While technically more difficult, an EVD offers an advantage in that it allows for both ICP monitoring and controlled drainage of cerebrospinal fluid (CSF) when ICP is elevated.
• ICP monitors should be placed in a portion of the brain that does not have eloquent function (typically the right side).
• ICP monitors are placed through a burr hole at Kocher’s point, which is 10–12 cm posterior to the nasion and 2–3 cm lateral to the midline (Figure 4).
• If a right-sided craniotomy is required, the ICP monitor should be placed on the left.

Preparation and Positioning

• Check for and reverse any coagulopathy.
• Administer prophylactic antibiotics.
• Position the patient supine in slight reverse Trendelenburg position, with the head midline and resting on a doughnut.
• The head should be stabilized (with tape or by assistant) while drilling to prevent skiving.
• Mark the midline and Kocher’s point (Figure 4).
• Shave the incision area and prep the entire head.

Insertion of External Ventricular Drain (EVD)

• A 2.5 cm linear incision (in the sagittal plane) is made centered over Kocher’s point (Figure 4).
• The hand drill in the cranial access kit is used to drill a hole with the bit locked at 1 cm (Figures 5a and 5b).
  • The drill bit will pass through the outer cortex, the cancellous bone, and then the inner cortex.
  • Don’t plunge into the brain. When the inner cortex has been breached, you will feel a sensation of the drill bit starting to be “pulled in.”
• The trocar is then inserted through the drill hole.
• The monitoring catheter is directed toward the medial canthus and advanced for about 5–7 cm until the lateral horn of the ventricle is cannulated (Figure 5c). Do not go any further. The catheter tip should be in the foramen of Monro.
• A popping is often felt when the ependymal of the ventricle is punctured.
• If the ventricle cannot be cannulated after three attempts, abort and proceed to inserting a bolt.
• Brisk flow of CSF confirms placement of the catheter tip in the ventricle.
• The catheter is stabilized at the skin and tunneled laterally from the incision (Figure 5d), taking care not to move the catheter either in or out.
• The trocar is removed from the distal catheter, and the catheter is attached to the connector and end cap.
• The scalp incision is closed with a running 3-0 nylon, and the catheter is secured to the skin (Figure 5e).
• Tip placement is confirmed with CT scan, if available (Figure 5f).
• The EVD collection system is primed with sterile saline. The catheter is attached, with the collection system leveled at the tragus of the ear.
• A standard arterial line pressure transducer is attached to continuously measure ICP.
• The height of the EVD is set at 0–20 cm H₂O, depending on the clinical scenario.
• The EVD can be clamped shut or opened to drain, with lower heights resulting in more CSF drained.

Insertion of Parenchymal Monitor (Bolt)

• A standard twist-drill hole is made at Kocher’s point, as above (Figure 4).
• The bolt is threaded into the burr hole (Figures 6a and 6b).
• The pressure transducer is inserted 1–2 cm into the brain parenchyma, taking care not to pass beyond the indicated mark on the catheter (Figure 6c).
• The catheter is secured and then attached to a monitor, allowing for continuous measurement of ICP (Figure 6d).

Exploratory Burr Holes

• Exploratory burr holes have limited practical utility. They should only be performed after consultation with a neurosurgeon (if possible) and only when CT scanning is not available to better guide management.

Decompressive Hemicraniectomy

Considerations

• Decompressive hemicraniectomy (DHC) is a surgical procedure used to relieve increased ICP in the setting of a large cerebral hemisphere mass or space-occupying lesion.
  • The term craniotomy is used when the bone flap is returned to its original location.
  • Craniectomy is used when the bone flap is not returned.
• The aim of DHC is to reduce ICP, improve blood flow, reduce damage to surrounding tissue, and reduce secondary brain injury.
• Evidence supporting emergent DHC in trauma is controversial. However, it does help control ICP and will allow evacuation to a higher level of care.

Indications for Decompressive Hemicraniectomy

• The classic indications for DHC are as follows:
  • Evacuation of mass lesions (primary hemicraniectomy)
    • Epidural hematoma ( > 15 mm in thickness or > 30 ml in volume)
    • Subdural hematoma ( > 10 mm in thickness)
      • For lesions < 10 mm, if there is decrease in GCS of 2, worsening pupillary exam, and/or ICP > 20 mm Hg
    • Middle fossa/temporal lobe hematomas with brainstem compression
      • Mass lesion with > 5 mm of midline shift on CT
    • Control of ICP (secondary hemicraniectomy)
    • Treatment of depressed or open skull fractures
• If CT scanning and prompt neurosurgical care are not available, one might consider performing DHC for damage control in patients with traumatic brain injury who have a life- threatening condition, deteriorating neurological status, or localizing neurologic signs (unilateral blown pupil).
• In the military setting, without neurosurgical specialty care available, DHC is recommended by current clinical practice guidelines for the following:
  • Patients presenting with severe closed or penetrating supratentorial brain injury, GCS of 8 or less, lateralizing cortical dysfunction to include unilateral mydriasis (blown pupil), hemiparesis accompanied by hemodynamic dysfunction manifested by hypertension, bradycardia, and respiratory variation (Cushing reflex)
  • Cases where maximal critical care management—including the administration of 3 percent saline, mannitol, sedation, HOB elevation to 30 degrees, drainage of CSF via EVD, etc.—fails to stabilize the patient. This may manifest as a new lateralizing cortical finding (hemiparesis, rapidly expanding pupil) and/or further decline in GCS when off sedation.

Preoperative Care and Positioning

• Maximize critical care management.
• Correct laboratory abnormalities as indicated.
• Correct coagulopathies.
• Give appropriate preoperative prophylactic antibiotics within one hour before skin incision.
• Position the patient supine with a shoulder roll under the ipsilateral shoulder.
• Tuck the arm on the operative side with the other left free for vascular access.
• Place a “doughnut” roll (or equivalent) under the patient’s head, which is then turned to expose the operative hemicranium (Figure 7).
• Shave, prep, and mark the incision site on the operative side.

Decompressive Hemicraniectomy: Surgical Procedure

• The most commonly used skin incision for DHC is a “reverse question mark” incision.
• This incision begins 1 cm anterior to the tragus of the ear at the level of the zygomatic arch and is curved superiorly and posteriorly around the ear, continuing posteriorly around the parietal eminence, or “parietal boss,” to just lateral to the midline and carried anteriorly to the hairline (Figure 8).
  • Do not cut below the zygomatic arch, as this risks injury to the facial nerve.
  • Avoid injury to the superficial temporal artery, which should lie anterior to the incision.
• The skin is incised down to bone, with division of the galea.
• If available, monopolar electrocautery should be used down to bone to minimize bleeding.
• Hemostatic (Raney) clips should be used on the skin edges, if available (Figure 9).

• The scalp and underlying muscle are reflected anteriorly as a myocutaneous flap, which is secured with hooks or towel clamps (Figure 9).
• The temporalis muscle is divided a couple of centimeters from its insertion on the cranium and is reflected with the myocutaneous flap (Figures 9 and 10).
• Burr holes are then drilled into the skull. The classically described DHC entails drilling five burr holes, as follows (Figure 11):
  • Burr hole 1 is drilled slightly superior to where the zygomatic process joins with the temporal squamous bone, just anterior to the tragus.
  • Burr hole 2 is drilled in the frontal bone just superior to where the sphenoid, zygomatic, and frontal bones converge, approximately 6 cm from burr hole 1. Care must be taken to angle the drill away from the orbit so as not to enter it with this hole.
  • Burr hole 3 is drilled in the posteromedial aspect of the parietal bone, with a minimum of 15 cm between this hole and burr hole 2. Care must be taken not to go too far inferior to avoid the transverse and sigmoid sinuses.
  • Burr hole 4 is drilled above and slightly anterior to hole 3 staying 3–4 cm from the midline of the skull to avoid entry into the sagittal sinus.

• Burr hole 5 is drilled above and slightly lateral to hole 2, staying 3–4 cm from the midline of the skull to avoid entry into the sagittal sinus.
• Additional burr holes may be required depending on the circumstances and are usually necessary if using a Gigli saw instead of a power saw.
• The bone flap should be a minimum of 12 × 15 cm in size, and the burr holes should be placed with this in mind.
• When creating burr holes, care should also be taken to avoid the frontal sinus.
• Burr holes are most easily made with a power drill (Figures 12 and 13). Most such drills have an automatic clutch that allows drilling to continue until the inner table is breached, at which point the drill will automatically stop.
• Saline is usually dripped with a syringe onto the skull at the site of the burr hole as it is drilled to minimize bone dust and prevent overheating of the drill bit.
• If adequate power (or equipment) is not available, a manual drill (Hudson brace type) can be used to make the burr holes (Figure 13).
• The manual drill requires significant effort on the part of the user, and its use should be practiced. Great care should be taken not to go too deep with the drill bit. Progress should be checked frequently, with the goal being to drill through the inner table until the dura is seen but not perforated.

• Once the dura is visualized, bone-cutting rongeurs and curettes can be used to expand the burr holes if needed.
• Once the burr holes have been created, the dura is carefully separated from the overlying bone through the burr holes using a Penfield dissector.
• The burr holes are connected using an electric bone saw or Duraguard router, sawing through the skull and taking care to leave the dura intact (Figure 14).
• If power or a power saw is not available, a Gigli saw (Figure 15) can be used to connect the burr holes as follows:
  • Additional burr holes may need to be created between the five standard ones to facilitate passage of the Gigli saw guard or conductor (a thin metal strip with a hook for the eyelet of the saw) between burr holes.
  • The dura is carefully separated from the interior skull with a Penfield dissector, enlarging the burr holes as needed with a rongeur to accommodate the end of the Gigli saw guard.

• The Gigli saw guard is carefully threaded from one hole to another, sliding between dura mater and skull, with the small hook on the guard facing outward (Figure 16).
• The eyelet of the Gigli saw is threaded onto the hook, and the guard is passed from one hole to the other, conducting the blade under the skull (Figure 16).
• The Gigli guard is left in place, providing additional protection to the underlying soft tissues.
• The Gigli handles are attached to each end of the saw, and the bone is cut by moving the handles back and forth. This is best accomplished with the saw held at a greater than 90° angle and not stopping until the cut is complete.
• The steps are repeated until all of the burr holes are connected and the bone flap is free.
• Once the bone flap is cut, it is gently lifted and slowly dissected from the underlying dura (Figure 17). This should be done slowly in a circumferential fashion, as lifting the bone flap at an angle will compress and increase pressure in the temporal lobe.
• Once the bone flap has been completely separated from the underlying dura, it is carefully lifted away.
• If the bone flap is to be saved, it is soaked in Betadine, rinsed with saline, wrapped in a soaked lap pad, and set aside until the end of the procedure, when it will be placed in the patient’s abdominal wall (extraperitoneally). Alternatively, the bone flap can be cryopreserved for future reimplantation.
• A rongeur is used to remove additional temporal bone (as needed) down to the floor of the middle cranial fossa, allowing for full decompression of the temporal lobe, which takes pressure off the brainstem.
• If the DHC was performed for an epidural hematoma, clot will be found on top of the dura after lifting off the bone flap (Figure 18a).
• The clot is gently removed from the dura (Figures 18b and 18c), and the bleeding from the superficial temporal artery is controlled, leaving the dura intact but separated from the surrounding edges of the skull (Figure 18d).
• Any residual oozing or minor bleeding is controlled with hemostatic agents such as gel foam.
• Though not universally practiced, it is recommended that the dura be tacked up to the skull via sutures placed through small holes drilled between burr holes 1 and 3, 3 and 4, 4 and 5, and 5 and 1—but not between 1 and 2 (Figure 19) or to the galea or periosteum of the skull.
• Take care not to place tack-up sutures into the dural sinus.

• These tack-up sutures are placed to close the epidural space to minimize the formation of a postoperative extradural hematoma.
• The dura can be opened using several different techniques, including cruciate, parallel-strip, or curvilinear (with or without radial “wheel spoke slits”) incisions (Figure 20).
• Whichever technique is used, it is advisable to place a 4-0 stitch in the dura to elevate it off the underlying brain tissue and then use a scalpel to make a small opening, which is then extended with Metzenbaum scissors.
• If there is significant ICP, opening the dura slowly can result in further damage and brain herniation through the incomplete incision, so the dura must be opened quickly once the incision is started.
• If the DHC was performed for a subdural hematoma, clot will be found on the surface of the brain when the dura is opened (Figure 21).
• The subdural clot should be gently swept/ scraped away from the surface of the brain using saline irrigation and gentle pressure (Figure 21).
• Once the subdural clot is removed, bleeding from the bridging veins and surface of the brain is controlled with bipolar cautery and hemostatic agents (Figure 22).
• Closure of DHC is accomplished as follows:
  • The dura is not closed. A dural substitute (such as DuraGen) is placed over the surface of the brain and under the cut dura.
  • A subgaleal Jackson-Pratt drain is placed and secured to the skin.
  • The galea is closed with interrupted sutures (2-0 VICRYL) spaced about 1 cm apart.
  • The skin is closed with staples after removal of the Raney clips.
  • Surgical dressing is applied.
• The head should not be wrapped, as this is compressive in nature and counteracts the goals of the surgery.