4 Decompressive Craniectomy for Intracranial Hypertension and Stroke, Including Bone Flap Storage in Abdominal Fat Layer

Introduction

The use of a decompressive craniectomy to treat the symptoms of intracranial hypertension was first proposed in the late 19th century by Sir Victor Horsley. ¹ Kocher popularized its use in Europe. Cushing introduced it in the United States in the early 20th century as a palliative treatment for multiple conditions causing intracranial hypertension, including tumors, hydrocephalus, and trauma. ² The operation fell into disfavor as advances in neurosurgery during the first half of the 20th century transformed most of the original indications for decompressive craniectomy into treatable conditions. In the 1970s, advances in life support increased the survival of patients with severe head injuries. This operation was revisited with the goal of treating traumatic brain injury patients with intracranial hypertension not responsive to “medical treatment.” ³ ^, ⁴ A collection of good results over the past two decades ⁵ ^– ⁷ has turned decompressive craniectomy surgery into an accepted option for the management of severe traumatic brain injury with refractory intracranial hypertension; new indications are being explored. Several studies have demonstrated a decrease in mortality and improved outcomes when this operation is performed in the correct patient population. ⁸ ^– ¹⁰

Indications

There is accumulated evidence to support the use of decompressive craniectomy for the following pathologies:
- Traumatic brain injury with diffuse or localized cerebral edema or multiple contusions refractory to medical therapy. ¹⁰
- Large cerebral infarctions resulting in severe edema and mass effect. ¹¹ ^, ¹²
- Some studies have shown promising results using decompressive craniectomy for other pathologies presenting with diffuse cerebral edema like aneurysmal subarachnoid hemorrhage, ¹³ venous thrombosis, ¹⁴ or infectious encephalitis, ¹⁵ but the available evidence is not strong enough to allow for a standard indication.
Two primary types of decompressive craniectomies are performed:
- Frontotemporoparietal (occipital) decompressive hemicraniectomy. This procedure is indicated for traumatic lesions or edema concentrated in one hemisphere with midline shift and risk of uncal herniation. This type of craniectomy may also be performed in the setting of an ischemic cerebrovascular event involving a unilateral, large vascular territory (usually middle cerebral artery [MCA] or internal carotid artery [ICA])
- Bifrontal decompressive craniectomy. This procedure is indicated in cases of diffuse, bilateral cerebral edema or in the setting bilateral frontal lesions with associated severe edema.
Decompressive craniectomy may be performed early or late ¹⁶ :
- Early decompressive craniectomy is performed soon after the patient arrives to the emergency department. Early craniectomy should be considered in patients with more than 5 mm of midline shift or if the midline shift is out of proportion to the size of the extra-axial mass lesion (usually hematoma) to be evacuated. ¹⁰
- Late decompressive craniectomy is usually performed within 48 hours of the original insult, in the setting of medically refractory elevated intracranial pressure (ICP; defined as ICP. 30 mm Hg for greater than 20 minutes by protocol at the authors’ medical center). Late decompressive craniectomy should only be considered after failure of primary tier therapy for intracranial hypertension.
- “Later” decompressive craniectomy—longer than 48 hours after the initial insult—may be indicated for patients who develop malignant edema following ischemic stroke, delayed expansion of contusions, or delayed malignant cerebral edema and/or hyperemic brain syndrome.

Preprocedure Considerations

Radiographic Imaging

Computed tomography (CT) is the most common imaging modality used to evaluate potential candidates for a decompressive craniectomy. CT images not only demonstrate acute intracranial pathology but also provide information concerning bony anatomic landmarks—useful for surgical planning—and allow for identification of skull fractures that might complicate the operation.

**Fig. 4.1a, b** Axial CT images for two patients—(a) one with traumatic brain injury and (b) one with a large right MCA stroke—selected for decompressive craniectomy.

CT angiography can be useful to diagnose major vascular occlusions and vascular injuries associated with head injuries, particularly when skull base fractures are present.
Magnetic resonance imaging (MRI) is used more sparingly in the context of trauma due to the added difficulty of organizing the logistics for life support in the MRI suite and the long duration of the study, which a critically ill patient may not tolerate. MR diffusion-weighted images are useful for early detection of large ischemic strokes. Early involvement of the neurosurgeon in such cases is essential in the event that later neurologic deterioration might provide an indication for emergent decompressive craniectomy.
Preoperative imaging ( Fig. 4.1 ).

Medication

If the patient is showing signs of imminent neurologic deterioration (dilated nonreactive pupil, hemiparesis, decerebrate or decorticate posturing), a bolus dose of mannitol (0.5 to 1 g/kg) can be administered as a temporizing measure en route to the operating room.
Perioperative antimicrobial prophylaxis should be administered within 1 hour of skin incision. The authors prefer cefazolin. In the setting of an open skull fracture and/or penetrating brain injury, triple antibiotic coverage (gram-positive, gram-negative, and anaerobic organisms) is initiated.

Operative Field Preparation

The hair is clipped with an electric razor. Any foreign bodies may be removed from the scalp at this time.
Hexachlorophene (or similar) soap is used to cleanse the skin, and then 70% alcohol is applied.
The skin incisions are marked, and povidone iodine or chlorhexidine may be applied as a final prep.
The surgeon also needs to make a decision at this time about how the bone flap will be preserved for future skull reconstruction. There is not enough evidence in the literature to support the preferential use of subcutaneous or cryopreservation. ¹⁷ ^, ¹⁸ In most institutions, sterile deep-freezing storage (280°C) is available. If storage is not available, or if the patient is anticipated to continue treatment at a different institution before the anticipated time of reconstruction, the surgeon should proceed to prep the abdomen for subcutaneous storage. We prefer to store the bone flap in the right lower quadrant of the abdomen. Many patients who sustain a traumatic brain injury will eventually need a gastrostomy tube, so the left side should be avoided. The right upper quadrant should be reserved in the event that the patient might require a ventriculoperitoneal (VP) shunt in the future.
Consideration should be given to perioperative placement of an invasive pressure monitor, contralateral to the planned surgical site. When feasible, placement of an external ventricular drain (EVD) is preferred. An EVD will permit both continuous assessment of ICP to guide therapy and therapeutic drainage of cerebrospinal fluid (CSF) for treatment of intracranial hypertension.

Operative Procedure

Decompressive Hemicraniectomy (Frontotemporoparietal [Occipital] Craniectomy)

Positioning (Fig. 4.2)

**Figure** Fig. 4.2 **Procedural Steps** The patient is positioned supine on the operating table. The head is secured with a three-point head holder and turned a minimum of 60 degrees (ideally 90 degrees) to the opposite side of the planned operation. Depending on the body habitus and flexibility of the neck, a roll under the ipsilateral shoulder may be needed to achieve the proper position. Ideally, the parietal eminence should be near parallel to the floor to avoid posterior sagging of the brain after the dural opening. **Pearls** • The frontal pin is placed on the midpupillary line contralateral to the side of the planned craniectomy. The two posterior pins should straddle the midline, above the transverse sinus. The posterior pins should not be placed laterally, toward the side of the craniectomy, to prevent compromising the posterior extent of the craniectomy. • If an ICP monitor has not been placed already, now is the time to do so. Usually, an entry point contralateral to the craniectomy is chosen. The catheter or wire should be tunneled away from midline to avoid interference with the incision.

Skin Incision (Fig. 4.3)

**Figure** Fig. 4.3 **Procedural Steps** For a standard hemicraniectomy, the incision will start at the level of the zygomatic arch, 1 cm in front the tragus, and extend superiorly and posteriorly in a reverse question mark fashion. The incision will end anteriorly at the hairline, close to midline. The skin opening technique varies with surgeon preference. The most expedient method that still minimizes blood loss should be used, since trauma patients often have already suffered severe hemorrhage and may be acutely anemic and hypovolemic. The authors prefer to open the skin with a no. 10 blade and to advance through the subcutaneous tissue with the monopolar. Focal bleeding points are controlled with both monoand bipolar electrocautery. Scalp clips are applied immediately to the skin edges to assist hemostasis. **Pearls** • In many patients, the superficial temporal artery (STA) can be palpated, and the incision designed to avoid it. Maintaining a patent STA will increase the viability of the flap. The posterior portion of the question mark should be kept uniform in width with the frontotemporal base of the flap to avoid a narrow, poorly vascularized distal end of the flap. This is achieved by allowing the reverse question mark to turn superiorly all the way to midline rather than directing it inferiorly into the territory mainly supplied by the occipital artery. A narrow or too caudally directed distal portion of the flap can result in tenuous perfusion, poor wound healing, or frank skin necrosis. • In cases of trauma, the flap should extend as posteriorly as possible to include the parietal eminence. In cases of ischemic stroke, the decompression area should be tailored to the margins of the infarcted area, allowing only the devitalized brain to bulge through the defect. • Once the whole incision is open and hemostasis has been achieved, the monopolar is used to cut the pericranium along the incision line. The temporalis muscle and fascia are also cut following the incision line.

Subcutaneous Dissection (Fig. 4.4)

**Figure** Fig. 4.4 **Procedural Steps** The pericranium is carefully separated from the skull using a Langenbeck type (square) periosteal elevator. A Hoen type (round) periosteal elevator is used to dissect the temporalis muscle. At the superior temporal line, the monopolar is often needed to dissect the more tenacious muscle insertion. **The resultant myocutaneous flap is reflected anteriorly to expose the bone. Retraction can be applied by using Fisch hooks or mini-towel clamps.** **Pearls** • The pericranium must be dissected carefully, without creating tears, since it will be used for the expansive duraplasty. The temporalis muscle must be dissected caudally until the root of the zygoma can be easily palpated to allow for access to the middle fossa. • A rolled lap sponge must be placed at the base of the flap, before applying retraction, to prevent kinking of the arterial supply and hypoperfusion of the flap during the procedure.

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4 Decompressive Craniectomy for Intracranial Hypertension and Stroke, Including Bone Flap Storage in Abdominal Fat Layer