Neurosurg Rev DOI 10.1007/s10143-015-0626-2

REVIEW

Does size matter? Decompressive surgery under review Arthur R. Kurzbuch 1

Received: 30 May 2013 / Revised: 20 September 2014 / Accepted: 19 January 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract In patients with traumatic brain injury (TBI) and ischemic hemispheric stroke (IHS), supratentorial decompressive craniectomy (DC) is performed when intracranial pressure (ICP) is unresponsive to medical treatment. There are numerous publications about the indications of supratentorial DC, the selection of patients eligible for surgery, the complications of the procedure, and the neurological outcome of operated patients. Only few papers, however, describe comprehensively the technical aspects of this procedure. DC consists of a variety of steps that can be conducted in different manners. Based on the literature reviewed, this article gathers features that had been developed with the intent to improve the decompressive effect of this surgery and evaluates if there is a strong recommendation for clinical practice. The existing literature does not supply class I evidence of how an ideal DC should be designed to reduce periand postoperative complications and to provide the best functional outcome.

Keywords Decompressive craniectomy . Durotomy . Intracranial pressure . Technique . Traumatic brain injury

* Arthur R. Kurzbuch [email protected] 1

Service of Neurosurgery, Neurocenter of Southern Switzerland, Ospedale Regionale di Lugano - Civico, Via Tesserete 46, 6900 Lugano, Switzerland

Introduction Decompressive craniectomy (DC) per se describes a craniotomy aiming for the decompression of the supratentorial intracranial space without reinserting the bone flap. The history of decompressive surgery may go back to Ancient Egypt and Ancient Greece. DC was practised since the beginning of the twentieth century in different manners to treat elevated intracranial pressure (ICP). In 1901, Kocher advertised decompressive surgery in posttraumatic brain swelling [43]. Cushing described in 1905 subtemporal craniectomy for patients with inaccessible brain tumors [16], for brain edema and swelling in bursting fractures of the skull [17]. Bauer in 1932 [8] and Clark et al. in 1968 [12] reported on circular decompression with dissatisfying outcome. Subtemporal and circular DC expose only a small surface of the underlying brain and have very limited decompressive effect. Later hemispheric DC was alternately favored and abandoned because of insufficient results. Since the 1970s, large fronto-temporo-parietal, fronto-temporo-parieto-occipital, bilateral, and bifrontal DC are regularly performed for various indications. Infrequent applications of DC are listed in Table 1. DC is nowadays mainly performed on patients with traumatic brain injury (TBI) and malignant edema from ischemic hemispheric stroke (IHS) as the last resort to treat medically intractable elevated ICP due to brain swelling. It is generally recognized that DC can decrease ICP and raise the survival rate [13, 78]. Nevertheless, DC is not undoubted. Sahuquillo concludes that the routine use of DC in TBI cannot be recommended in patients older than 18 years of age; only as a rescue therapy it would be acceptable [66]. In patients with TBI, the DECRA study found that DC decreased ICP but was associated with worse functional outcome of surgically treated patients [13]. The results of this study are still discussed [67]. The ongoing prospective multicenter randomized controlled RESCUEicp

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study compares the outcome of patients undergoing large DC to those patients with medical treatment [31]. For ischemic stroke, three randomized controlled trials (DECIMAL, DESTINY, and HAMLET) showed significant reduction in mortality in operated patients over those with conservative treatment and an increased number of patients aged between 18 and 60 years with favorable functional outcome if DC is performed within 48 h of stroke onset [75]. Compared to the vast number of publications regarding patient selection, there are only few papers outlining specifically the technical facets of the surgical procedure [27, 30, 33, 62, 63]. DC is composed of numerous steps that can be accomplished in varying ways and some of them may be vital for the outcome by influencing the decompressive effect of the procedure. DC is considered as a technically straightforward [28, 29, 74] but not a simple operation [48]. Stiver [71] highlights the complications of DC: blossoming of contusions, evolution of contralateral mass lesions, external cerebral herniation, subdural effusions or hygromas, paradoxical herniation, impaired wound healing and infection, hydrocephalus, syndrome of the trephined, bone resorption, and persistent vegetative state. Also epilepsy and CSF leakage through scalp incisions are described [28, 82]. This review aims to provide a compilation of the technical facets of DC performed for TBI by filtering those features that enhance the decompressive effect and evaluates if there is a strong recommendation for clinical practice. An online research for literature in PubMed was performed on October 24th, 2012. The search term Bdecompressive c r a n i e c to m y te c h n i q u e ^ g e n e r a t e d 7 0 t i t l e s a n d Table 1 surgery

Infrequent indications for supratentorial decompressive

Pathology

Reference

Herpes simplex encephalitis

Bayram et al. [9] Yan [80]

Encephalitis

Aghakhani et al. [2] Taferner et al. [73] Schwab et al. [69]

Empyema

Aghakhani et al. [2]

Methadone intoxication

Aghakhani et al. [2]

Meningoencephalitis

Aghakhani et al. [2]

Reye’s syndrome

Aghakhani et al. [2] Ausman et al. [7] Chi et al. [10]

Aneurysmal subarachnoid hemorrhage

Arikan et al. [6] Güresir et al. [25]

Toxoplasmosis Dural sinus thrombosis

Agrawal and Hussain [3] Stefini et al. [70] Lanterna et al. [47]

Lead encephalopathy

McLaurin and Nichols [51] Greengard [22]

Bdecompressive craniectomy technical^ 20 hits. The inquiry was repeated on April 10th, 2013 and provided ten more results for the first search term and one further paper for the second. Papers were selected on the basis of the title, abstract, and key words. Copies of the articles were printed or ordered to verify whether they contain information of the aspects of DC. The reference section of these articles was also checked for pertinent information and the papers obtained if they proved to be relevant.

Background of decompressive surgery Compression—decompression According to the Monro-Kellie hypothesis, compression of the rigid cranial compartment with elevation of ICP arises as soon as the capacity of compensation systems is exhausted. Edema and ICP being part of a dynamic system can rise postoperatively. Thus, solely eliminating preoperatively existing compression may be insufficient. The aim is also to create a novel reserve capacity to accommodate space claiming elements to develop. In this context, the term Bdecompressive craniectomy^ seems imprecise and the description Bspace gaining surgery^ may be more accurate to clarify the two components of the procedure. Structures causing elevated ICP The head can be divided into extracranial, obligatory intracranial, and optional intracranial sections. Table 2 mentions the individual structures and their role in the context of compression and elevated ICP. The cephalic bone and the dura as restrictive factors as well as optional intracranial space occupying elements are potentially responsible for elevated ICP. These structures have to be overcome when elevated ICP turns out to be recalcitrant to medical treatment and indication for surgical treatment is provided. When opening the skull, the preoperative extra- and intracranial compartments of the head merge and become a single unit. Consequently, the number of possible restrictive structures postoperatively increases as the scalp with the galea and the temporal muscle get in direct contact with the intracranial structures.

Surgical targets for space gaining maneuvers in supratentorial DC All extra- and intracranial structures can be the target of surgery (Table 3).

Neurosurg Rev Table 2 Extra- and intracranial structures contributing to compression and elevated intracranial pressure (ICP)

Extracranial

Intracranial

Scalp with galeaa a

Temporal muscle Cephalic bonea, b

Obligatory

Optional

Duraa, b

Edemac, d

Brain Intravascular blood volume Cerebrospinal fluid

Hematoma

Epiduralc, d Subduralc, d Intracerebralc, d

Contusionc, d Hydrocephalusc, d a

Potentially postoperatively restrictive

b

Potentially preoperatively restrictive

c

Potentially contributing to preoperatively elevated ICP

d

Potentially contributing to postoperatively elevated ICP

Skin incision The shape of the cutaneous incision depends on the localization of the DC that can be performed unilaterally, bilaterally, stepwise bilaterally, and bifrontally. Incisions visualizing anatomical landmarks as the sagittal suture, the upper point of the zygoma, and the lambdoid suture reduce the risk of injury of the superior sagittal sinus (SSS) and the transverse sinus and to perform too small craniotomies. For unilateral surgery, mainly three variants of incision are used: the increased Btrauma flap^ or expanded Breversed question mark incision,^ the BT-incision,^ and the Binverse U-incision.^ The incision for the increased Btrauma flap^ (Fig. 1a) begins no more than 1 cm anterior to the tragus. It then curves in the form of a question mark around the top of the pinna posteriorly to the occipital region, passes the lambdoid suture, and runs up to and then follows the midline to reach the hairline with a short incision of about 1 cm directed to the contralateral side. To reach more posteriorly, Johnson et al. propose to add a short relieving incision in the occipital region [33]. The Table 3 Overview of surgical targets for space gaining maneuvers in supratentorial decompressive surgery

superficial temporal artery (STA) with its frontal and parietal branches that supply the lateral territory of the scalp is preserved. The posterior auricular artery (PAA) and the occipital artery (OA) with its branches, however, may be incised depending on the inferior and posterior extension of the cutaneous incision. A small question mark incision that runs too far from the midline and does not reach the hairline may cause impaired wound healing due to insufficient blood supply as the width of the flap may be too small at the ratio of its length. Furthermore, a small skin incision limits the exposure of the bone and the size of the craniectomy. The BT-incision^ (Fig. 1b) that exposes also the aforementioned landmarks was described by Kempe for hemispherectomy [39]. The BT^ consists of two straight elements: a fronto-occipital midline incision and a perpendicular incision going down from about 2 cm posterior to the coronal suture just anterior to the tragus. This incision sacrifices the parietal branch of the STA and preserves the PAA and OA. The inverted BU-incision^ (Fig. 1c) runs from the frontal to the occipital region reaching the midline [33]. This incision eliminates the risk

Surgical target structure

Procedure

Scalp with galea Temporal muscle Skull bone

Galeotomy, scalp plasty Partial resection Craniectomy: unilateral, bilateral, bifrontal approach; craniotomy with reinsertion of bone flap; osseous decompression extending to the temporal floor; osseous thinning, smoothen borders Durotomy, duraplasty Vascular tunnel Evacuation Resection, partial lobectomy Cerebrospinal fluid drainage Subgaleal wound drainage

Dura Vessels Hematoma (epidural, subdural, intracerebral) Contused, infarcted, edematous brain Cerebrospinal fluid, hydrocephalus Prophylactic procedure

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more difficult to fold the temporal muscle inferiorly. This may limit the exposure of the temporal bone necessary for decompression. Innervation and vascularization of the temporal muscle and the integrity of the muscle fibers can be compromised. The resulting edema of the muscle may further impede the access to the floor of the middle cranial fossa and the decompression of the temporal lobe. Postoperatively, muscle function may be affected. An artificial dural substitute can be laid between the dura and the internal surface of the temporal muscle to avoid the formation of adhesions thereby facilitating cranioplasty with less temporal muscle damage, operation time, and blood loss [38]. With the removal of the cephalic bone, the elevated edematous temporal muscle becomes part of the intracranial compartment and, thus, a space occupying intracranial element. Park et al. [59] propose after surgery on 15 patients partial resection of the temporal muscle and fascia down to the upper part of the zygoma that corresponds to the floor of the middle cranial fossa. When performing cranioplasty, they positioned a prosthesis to fill the muscle defect with minor esthetic and mechanical masticatory impairment. Craniotomy—size Fig. 1 Schematic drawings of the head illustrate the cutaneous incisions (dashed lines) for decompressive craniectomy. Unilateral frontotemporo-parieto-occipital approach (a–c) in lateral view and bifrontal approach (d) in anterior top-down view: increased Btrauma flap^ with optional posteriorly directed incision (a), BT-incision^ (b), inverse BUincision^ (c), and bicoronal incision (d)

of a lesion of the STA and the PAA, whereas the OA may be incised. For the bifrontal approach (Fig. 1d), a bicoronal incision begins no more than 1 cm anterior to the tragus. It follows a line that lies about 1 cm posterior and parallel to the coronal suture and reaches the corresponding starting point on the contralateral side. There is no study that concludes a strong recommendation of one specific skin incision.

Temporalis muscle The skin flap and the temporal muscle can be elevated in two layers with interfascial [84] or subfascial dissection of the frontotemporal branch of the facial nerve and retrograde subperiostal dissection [36, 58] of the temporal muscle. The separation of the skin flap from the muscle allows to fold the muscle inferiorly with sufficient exposure of the inferior part of the squamous portion of the temporal bone. This is important for the decompression of the temporal lobe. Alternatively, the skin and the temporalis muscle can be raised in one layer. The elevation of a myocutaneous flap is less time consuming than the two layer technique but makes it

An important role is attributed to the size of craniotomy in decompressive surgery. If the elevated bone flap is too small the expanding brain can herniate already during the intervention through the cranial defect, thus creating its strangulation also known as external brain hernia, fungus cerebri [74], mushrooming, or erectio cerebri [20]. Very large bone flaps increase the risk of damaging structures (e.g., SSS, bridging veins, transverse sinus) and may favor postoperative complications like hydrocephalus or the syndrome of the trephined. Wirtz et al. [79] found in a geometric model the nonlinearity of the diameter of craniectomy and the gained volume. The dimensions of the craniotomy vary widely in the reviewed literature between Bmore than 8 cm^ and Bat least 15 cm^ and result from case series (Table 4). The existing literature does not provide class I evidence for the size of the bone flap in space gaining surgery. Craniotomy—unilateral approach Craniotomy for a unilateral approach is performed in the fronto-temporo-parieto-occipital or the fronto-temporoparietal area. The anterior-posterior and superior-inferior extension determine the size of the craniotomy. The anatomical landmarks of the craniotomy are anteriorly the orbital rim and the frontal sinus, posteriorly the lambdoid suture, superiorly the SSS, and inferiorly the upper point of the zygoma that corresponds to the floor of the middle cranial fossa. The dimension of the frontal sinus should be

Neurosurg Rev Table 4

Size of supratentorial decompressive craniectomy for unilateral approach

Diameter

Length×width

Distance to midline

Equal or more than 8 cm

Kunze et al. [46]

8×10 cm, 12×15 cm

Yang et al. [82]

11×16 cm

Güresir et al. [26]

0 cm

Kunze et al. [46]

10–11 cm

Csókay et al. [14]

1.0–1.5 cm

Güresir et al. [26]

More than 11 cm

Csókay et al. [15]

1.5 cm

Güresir et al. [25] 2009

At least 12 cm

2 cm

Ragel et al. [63]

At least 15 cm

Timofeev et al. [74] Michel et al. [54] Güresir et al. [25]

>2.5 cm

De Bonis et al. [18]

12–15 cm

Valença et al. [76]

2.5–3 cm

Timofeev et al. [74]

verified on the CT scan to avoid its opening. If the frontal sinus is entered, it should be cranialized to reduce the risk of postoperative CSF leak and infection. For fronto-temporo-parieto-occipital craniotomy (Fig. 2a), the bone flap reaches the occipital region by placing a burr hole medially to the lambdoid suture [25, 26] (Fig. 2b). Respecting posteriorly, a line parallel and above the zygoma minimizes the risk of lacerating the transverse or sigmoid sinus. To avoid lesions of the SSS or the bridging veins, the craniotomy should not be closer than 2 cm to the midline. De Bonis et al. [19] propose in a retrospective review of 26 patients to place the superior border of the craniotomy at least 25 mm off the midline to reduce the risk of postoperative hydrocephalus. Caudally, the craniotomy extends to the floor of the middle cranial fossa to prevent brain stem compression by the temporal lobe. The inferior part of the squamous portion of the temporal bone is carefully removed with bone

Fig. 2 Pictures of the skull reflect the craniotomy line (dashed lines) with temporal extension (solid lines) of unilateral frontotemporo-parieto-occipital (a, b) and bifrontal (c, d) decompressive craniectomy. a Lateral view of a craniotomy line for a large frontotemporo-parieto-occipital craniectomy going down to the temporal floor. b Posterior view of a shows a burr hole (solid circle) placed medially to the lambdoid suture to include the occipital region in the craniectomy line. c Antero-lateral top-down view of a bifrontal craniectomy line reaching the floor of the middle cerebral fossa. d Antero-lateral top-down view of a bifrontal craniectomy line to lift two bone flaps that leave a bone strip over the superior sagittal sinus

rongeurs down to the temporal cranial base (Fig. 2a) [25, 26, 62]. In doing so, the creation of fractures or the expansion of preexisting traumatic fractures that might cause bleeding may be avoided. Münch et al. [57] state in a retrospective study of 49 patients the importance of the caudal extension down to the temporal base over the size of the craniectomy. The reviewed literature does not support strong recommendation for the positioning and local restriction of the craniotomy. Craniotomy—bifrontal approach The anterior border of the bifrontal craniectomy (Fig. 2c) represents the orbital rim; posteriorly, the craniectomy extends to or 1 cm behind the coronal suture. Depending on the pneumatization of the frontal bone, sparing of the frontal sinus may not always be feasible. If it is entered, it should be cranialized. A vascularized periostal flap can be elevated to

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place it over the cranialized frontal sinus. Caudally, the osseous decompression goes down to the floor of the temporal fossa. The bone flap is elevated in one piece. Alternatively, it can be divided in a smaller and a larger part by adding a unilateral parasagittal craniotomy line. After removal of the smaller bone flap, the SSS can be exposed under vision what may minimize its injury. Then the second and larger bone flap is raised. Another technique is to lift one bone flap on each side at which the SSS remains covered by bone (Fig. 2d). Handling of the bone flap At the end of the craniotomy, the raised bone flap can be left out corresponding literally to the term craniectomy. Alternatively, the bone is reinserted immediately. Leaving the bone flap out If the bone flap is not put back, it is either discarded or preserved in different ways outside or in the patient’s body to be available for later cranioplasty. External storage comprises freezing, radiation, or sterilization in various manners. For internal preservation, the bone flap can be placed in abdominal subcutaneous tissue. Alternatively, the bone flap is inserted in a subgaleal pouch created by blunt or sharp dissection [45, 60]. As the scalp covers the bone flap positioned under the galea, there is less skin at disposal to accommodate brain exceeding the margin of the craniotomy. Hence, the decompressive effect may be reduced. Immediate reinsertion of the bone flap or substitutes Different strategies were developed to combine in one operation the decompressive effect of craniectomy with the advantages of cranioplasty that traditionally was performed at timely distance. Khoo depicts in a technical note the Breplacement of a self-adjusting^ bone flap [41]. Pieces of Raimondi catheter tube are inserted and fixed in holes drilled on the cut surface of the bone flap and the margin of the craniotomy. These constructs act like Bspring catheter connections^ that allow the inward and outward movement of the bone flap according to the protruding brain. For the Bhinge^ technique [21, 35, 44, 68] (Fig. 3a), the raised bone flap is reinserted and either fixed or approximated with sutures or metal plates to the frontal or upper border of the craniotomy. An additional plate fixed only to the bone flap avoids its subsiding. The creation of oblique cut surfaces by using a Gigli saw also prevents the bone flap from sinking. Alternatively, the craniotomy flap remains attached to the temporal muscle and pericranium that act as a hinge [1, 56]. To gain more space intracranially, the internal tabula of the

bone flap can be milled off. Valença et al. [76] modify the raised craniotomy flap by cutting it vertically into two approximate sized parts. The lateral borders of the resulting pieces are fixed with two sutures to the margin of the craniotomy (Fig. 3b). Thus, hinged to the skull, the two bone flaps can open like window lids (Bin-window craniotomy^) in function of the underlying protruding brain. Inclining the craniotome prevents the bone flap from subsiding later. Peethambaran and Valsalmony [61] propose a similar procedure referred to as Bfourquadrant osteoplastic decompressive craniectomy^: They cut the bone flap crosswise to obtain four similar pieces they fix loosely among each other and to the margin of the craniotomy. In a bifrontal craniotomy, Valença et al. [77] reinsert immediately and hinge the bone flap to the skull posteriorly with two sutures (Bcar hood decompressive craniotomy^) (Fig. 3c). In the area of the hinge, the decompression is less effective due to the reduced range of motion of the bone flap. The hinge should therefore be placed far away from the base of the temporal fossa. To avoid this disadvantage of hinges, Ahn et al. perform the Bin situ floating resin cranioplasty^ [4]. A 1-mm-thick resin flap that is about 5 mm larger than the original bone flap and that can ride freely on the escaping brain is molded intraoperatively, implanted, and fixed loosely with sutures. All hinge techniques imply that the volume that is at disposal for the protruding brain under the scalp is detracted from the volume of the reinserted bone flap that may compromise the decompressive effect. Kenning et al. [40] compare in a retrospective review hinge craniotomy (HC) to DC in 50 patients and find that HC seems to be at least as good as DC concerning postoperative ICP control and equivalent early clinical outcomes. Kano et al. [37] found in a retrospective study of 58 patients HC with ICP monitoring effective and safe without a significant difference in outcome. Craniotomy margins Flattening of the sharp surface of the craniotomy border reduces the risk of injury of exceeding brain [74, 76]. Durotomy—duraplasty It is generally recognized that decompressive surgery reduces ICP in a double stage manner with removal of the bone flap and subsequent durotomy [34, 65, 85]. Dura opening is essential for the decompressive effect and as a space gaining maneuver. Numerous fashions of opening the dura are used when performing unilateral decompressive surgery: stellate [15, 33, 44, 62], star-shape [15] or cruciate (Fig. 4a), fish

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Fig. 3 Illustration of the hinge technique of supratentorial decompressive surgery. Dashed line: craniotomy line. Solid line: Margin of the bone flap. Curved arrows: indicate mobility. a The raised bone flap of a unilateral fronto-temporo-parieto-occipital craniotomy is reinserted and anteriorly attached with screws and plates to the skull, whereas the posterior plate is

only fixed to the bone flap (lateral view). b The parts of the bisected bone flap of an Bin-window craniotomy^ are only laterally attached to the skull with sutures and can move outwards (lateral view). c A bifrontal bone flap fixed posteriorly with sutures to the skull can move upwards, Bcar hood decompressive craniotomy^ (antero-lateral top-down view)

mouth (Fig. 4b), horseshoe, dovetail [33], semicircular [62], C-shaped fashion with spoke-wheel relief cuts durotomy [27, 63] (Fig. 4c), and a U-shaped incision based on the sphenoid wing [74] (Fig. 4d). Mracek et al. [56] present a large curved incision with convexity toward the skull base (Fig. 4e). For bifrontal decompressive surgery, Kjellberg and Prieto [42] opened the dura Bfish mouth^ like with incisions parallel to the anterior and caudal border of the craniotomy, directed toward the SSS, and additional incisions close to the pterion. Timofeev et al. [74] propose a BU-shaped^ durotomy pediculated to the SSS. Quinn et al. [62] illustrate a SSS-based shaped dural opening with an incision going down to the floor of the temporal fossa (Fig. 4f). To allow better distension of the swelling brain, two silk ligatures can be applied to the most anterior part of the SSS. The SSS between the ligatures as well as the falx cerebri are then cut through with care to avoid parenchymal and vessel injury [42, 62, 74] (Fig. 4g). Dural opening for a bifrontal craniectomy at which the SSS remains covered by bone is illustrated in Fig. 4h. Yao et al. [83] present a gradual crosswise durotomy and duroplasty performed in 12 patients. Likely that gradual opening of the dura lowers the possible damage of the underlying brain compared to the abrupt loss of counterpressure due to instantaneous complete durotomy.

Like the size of craniotomy, the size and fashion of dural opening are important: If the durotomy is too small, the brain can be compressed under the dural edges, and if the opening is too large, postoperative hydrocephalus or the syndrome of the sinking flap may be favored. After the decompression, the dura is left open. Alternatively, duroplasty that furnishes additional space to envelop the swelling brain with autograft (vascularized periostal flap) or allograft material may be performed. Dura closure with a dural substitute may raise the risk of infection [50]. Different sheets of artificial materials are used as dural graft as well as anti-adhesion barrier. These membranes may be sutured to the margins of the durotomy or are laid sutureless on the cerebral cortex under the dura or onto the dura. Mitchell et al. [55] perform a Blattice duroplasty^ without inserting additional material (Fig. 4i) for the purpose of stepwise pressure reduction and to limit the protrusion of the underlying brain. They cover the exposed dura with a rectangular lattice composed of parallel rows of straight 2-cm-long staggered incisions. Duroplasty may decrease the incidence of postoperative subdural effusion [81], CSF leakage, and wound breakdown with subsequent infection. The necessity of dural closure, however, is still under debate. Güresir et al. conclude that duraplasty is not

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Fig. 4 Durotomy (dotted lines) of supratentorial decompressive surgery (dashed lines: craniotomy lines). Stellate, star-shape, or cruciate (a); fish mouth (b); C-shaped with spoke-wheel relief cuts (c); U-shaped based on the sphenoid wing (d); and curved with convexity to the skull base (e) durotomy for unilateral fronto-temporo-parieto-occipital surgery (lateral view). f Dural incision for bifrontal decompressive craniectomy extending to the temporal floor (antero-lateral top-down view). g In

bifrontal craniectomy (antero-lateral top-down view), the superior sagittal sinus (gray rectangle) is cut anteriorly with the falx (black solid line) between two ligatures (black solid circles). h Durotomies in bifrontal craniectomy with a bone strip left over the superior sagittal sinus (anterolateral top-down view). i Dural opening in the form of a mesh of straight dural incisions (Blattice duroplasty^) for unilateral fronto-temporoparieto-occipital decompression (lateral view)

necessary [26]. They open the dura in a stellate manner and leave it unsutured. The dura and the underlying brain

are then covered by hemostatic material. They found that the Brapid closure technique^ saves operation time and

Fig. 5 a Illustration of a cushion made of a folded rectangular piece of hemostatic sponge and tightened with absorbable thread wound around (anterior top-down view). The cushion acts as a spacer in the subdural space. b Two-dimensional delineation of a subdural Bvascular tunnel^:

The cushions (k) depicted in a act as a protective spacer between the vessels (h) and the overlying dura (b) when brain ( f ) protrudes because of edema (g, arrows). Cephalic bone (a), subdural space (c), arachnoidea (d), pia (e), protective space (double arrows)

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does not create problems to find a dissection plane when performing cranioplasty. There is no study that concludes the superiority of one specific durotomy or duroplasty. Vessels After dura opening as well as postoperatively, brain swelling may cause herniation of cerebral tissue with compression of superficially running vessels under the border of the durotomy. Csókay et al. [14, 15] describe the creation of a protective vascular tunnel performed in 20 patients by placing cushions parallel and on both sides of major vessels at the margins of the durotomy. These pillars maintain the distance between the swelling brain and the overlying dura, thus protecting the vessels that run between the spacers from compression (Fig. 5a, b). Hemorrhages in TBI The removal of epidural and subdural hematomas is generally accepted and performed. The beneficial effect of early evacuation of traumatic intraparenchymal hematomas or contusions is still under debate. International multicenter trials are conducted [24, 52, 53]. Removal of contused or infarcted brain The resection of brain tissue as a space gaining maneuver during decompressive surgery is only exceptionally practiced. Primarily, temporal [86] or anterior temporal lobectomy [11, 32] was described for patients with traumatic temporal lobe contusions or hemispheric stroke [23]. CSF—hydrocephalus According to the Monro-Kellie rule, external ventricular drainage reduces ICP, and consequently, CSF drainage is practiced usually before DC [49]. As the correct positioning of an external ventricular catheter may be technically difficult when ventricles are displaced and narrow due to compression by edematous brain, neuronavigation may be useful. The volume of CSF that can be derived may be too little to lower ICP sufficiently. When external ventricular drain insertion has to be performed at the same time as decompressive surgery, the catheter should be placed before and on the contralateral side of the craniectomy. Thus, ventricular drainage with reduction of ICP can already start before decompression, and neuronavigation can be used that might otherwise lose its accuracy due to the displacement of the brain after decompression. Another advantage of contralateral placement of the EVD is that it is less prone to displacement due to the expanding brain on the decompressed side.

Scalp with galea—wound closure Relaxing incisions of the rigid galea aponeurotica [64] enlarge the inner surface of the cutaneous flap and the volume of the underlying decompressed intracranial compartment. Wound closure over massively swollen brain thus exerts less pressure. Akutsu et al. [5] performed a plasty of the scalp with artificial dermis in five patients with severe TBI to gain additional space. Prophylactic procedures Subgaleal wound drainage derives blood and wound fluid that postoperatively compresses the dura and the underlying brain. If duroplasty is not performed, a subgaleal drainage may favor infection and CSF absorption problems. Sughrue et al., however, inserted in 127 patients who underwent DC without dural closure two Jackson Pratt drains. They were left in place for 3 to 8 days without complications [72].

Conclusion The history of supratentorial space gaining surgery as part of the armamentarium to treat elevated ICP is characterized by the ingenuity to optimize the decompressive effect of the intervention and to accommodate postoperatively swelling brain. Various technical measures had been tried for all involved intra- and extracranial structures. The published innovations that might be intuitively plausible are often experiences of a single institution with few patients treated. The literature reviewed does not supply class I evidence that the improvement of the decompressive effect of single features reduces peri- and postoperative complications and furnishes a better functional outcome of the operated patients. Consequently, there is at present no undoubted design of an ideal decompressive surgery. For the efficacy of DC, it is indispensable to understand the pathophysiological processes and time course of TBI and HIS and the effect of the single decompressive maneuvers on these processes. Therefore, studies are needed that elucidate the nature and time course of brain edema formation and the effect of shear forces on the brain tissue. This knowledge may help to create a model of space gaining surgery that could serve as subject to further studies. Conflict of interest The author declares that he has no conflict of interest or financial disclosure.

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Comments George M. Ghobrial, Jack Jallo, Philadelphia, USA Decompressive hemicraniectomies remain in practice as an emergency, cost-effective, tried, and true measure in a neurosurgeon’s armamentarium for the life-sparing treatment of malignant intracranial hypertension in the setting of traumatic brain injury, extra-axial intracranial hemorrhage, and malignant infarction. Varying surgical techniques are encountered in prospective studies and operative atlases, while nuances and refinements are passed down over each generation through tradition and residency training. While the general goals of surgery remain the same—for the rapid relief of intracranial hypertension and the decompression of the brainstem and critical structures—considerable variation in technique is encountered. The authors set out to answer the question as to what specific technical specifications that contribute to the variation in this technique are supported in the medical literature by way of highquality medical evidence through a review of the literature. The authors

encounter numerous studies demonstrating the early benefits of emergency decompression through lowered mortality. Unsurprisingly, they encounter very few publications addressing various technical nuances, such as an ideal craniectomy flap size. In the question of the benefit of maximizing the craniectomy flap to the fullest extent possible, which for many is the overarching goal of decompression, support is encountered in retrospective studies that larger is better—particularly an improvement in mortality when the anteroposterior diameter exceeded 10 cm.1 While this question seems intuitive to many neurosurgeons, this study highlights the scarcity of high-quality literature in a procedure performed at a relatively high volume. Importantly, this manuscript highlights the fact that level I studies providing favorable2 and unfavorable3 evidence for intervention are performed with different techniques which are not well evaluated in the literature.

References 1. Sedney CL, Julien T, Manon J, et al. The effect of craniectomy size on mortality, outcome, and complications after decompressive craniectomy at a rural trauma center. Journal of neurosciences in rural practice 2014;5:212–7. 2. Vahedi K, Vicaut E, Mateo J, et al. Sequential-design, multicenter, randomized, controlled trial of early decompressive craniectomy in malignant middle cerebral artery infarction (DECIMAL Trial). Stroke; a journal of cerebral circulation 2007;38:2506–17. 3. Cooper DJ, Rosenfeld JV, Murray L, et al. Decompressive craniectomy in diffuse traumatic brain injury. The New England journal of medicine 2011;364:1493–502.