Skull Base Reconstruction Treatment & Management

Updated: Nov 17, 2015
  • Author: Mario J Imola, MD, DDS, FRCS, FACS, FRCSC; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Treatment

Preoperative Details

A wide variety of options, ranging from grafts and alloplastic implants to local, regional, and distant revascularized free flaps, are available for skull base reconstruction (see the summary of options for skull base reconstruction, below).

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Options for skull base reconstruction

Grafts

Grafts are free nonvascularized pieces of tissue, which are transferred into a defect, that initially heal by passage of nutrients into the graft cells via diffusion from the recipient bed. Over a period of days to weeks, angiogenesis causes revascularization of the graft, a process by which new blood vessels grow into the graft tissue. Advantages of tissue grafts include relatively easy harvest and insetting with minimal donor site morbidity. The single major disadvantage is the very limited ability to reliably repair extensive defects using grafts because of an absent blood supply immediately after tissue transfer. Large pieces of nonvascularized tissue undergo partial or complete necrosis, particularly in a hypovascular recipient surgical bed, as occurs with preexisting radiation or surgical scarring. Contamination of grafts placed into mucosal surface defects also decreases chances of survival.

In the past, skin grafts have been placed directly over the dura or even onto dural patches, resulting in an unacceptable rate of graft loss with subsequent dural exposure, cerebrospinal fluid (CSF) leak, and fulminant meningitis, eventually leading to death in some cases. The risk of graft necrosis when used as the only barrier over exposed portions of the carotid carries potentially lethal consequences. As such, the authors recommend that larger areas of dura and carotid segments exposed to the upper respiratory tract be covered with vascularized tissue to reduce the possibility of CSF leak, intracranial infection, or arterial rupture.

Currently, the principal uses of grafts in skull base reconstruction are as (1) fascial grafts used as dural patches, (2) fat or dermal-fat grafts used to obliterate relatively small well-contained cavities and restore lost soft tissue bulk, and (3) bone grafts used to restore resected osseous structure in critical locations.

  • Fascia grafts: These grafts are usually available within the local field by harvesting from the deep temporal fascia or from pericranium, which although technically not a fascial layer, handles similarly surgically. Both materials can be successfully used to patch holes in the dural cover, but the superficial layer of deep temporal fascia provides a thicker, more durable membrane than pericranium. Temporal fascia is in more limited supply when a single piece is desired to close large defects. In cases of recurrent tumor with depletion of local fascial stock during previous surgery or in cases of extremely large dural defects, harvest of readily obtainable distant fascia (eg, fascia latae of the lateral thigh) may be necessary. [3]
  • Fat and dermal fat grafts: Most commonly, these materials are taken from the abdomen through a periumbilical incision. Fat grafts are typically used in small-to-moderate sterile cavities as commonly occur following lateral skull base surgery of the middle and posterior cranial fossae. Disadvantages include a volume reduction of up to 50% over time and an inability to heal in the setting of wound infection, necessitating removal of the fat. Communication of the resection cavity with mucosal surfaces is a contraindication to fat grafting; prior radiation is a relative contraindication.
  • Bone grafts: These grafts are readily obtained as split-thickness calvaria, which can be harvested from the inner table of bone segments removed during the craniotomy access or separately as outer table grafts from intact portions of the parietal bones. If the skull has been depleted previously or very large quantities of bone are required, the iliac crest is a suitable second-choice source for bone grafts. Note that many osseous defects of the skull base can go unrepaired without significant deformity or dysfunction.
  • Allografts: These tissues are obtained from human sources and are treated appropriately before use in patients to eliminate or greatly reduce risk of microbial transmission. Various materials are available as allografts, including lyophilized dura, freeze-dried bone, chemically treated acellular dermis, and fibrin glue. In general, allografts tend to survive less well than autografts but bear consideration when autogenous tissues are otherwise lacking.

Local flaps

Local flaps involve the transfer of vascularized tissue located adjacent to the defect under reconstruction. The flap tissue is mobilized and repositioned into the defect using various techniques such as rotation, transposition, or advancement. The blood supply to local flaps is via the preservation of a vascular pedicle at the base of the flap, which maintains continuity with the donor site following transfer. Advantages of local flaps are (1) location within the operative field of skull base procedures, (2) relative ease of dissection, and (3) generally, little donor site morbidity. Unfortunately, well-vascularized tissue with sufficient bulk for use as a reliable local flap in the cranial base region is generally in short supply. This situation is particularly true for larger defects located deep within the skull base.

  • Forehead and scalp flaps
    • These flaps are local cutaneous tissue transfers that were some of the earliest methods available to repair skull base defects. The midline forehead and extended glabellar flaps are based on the supratrochlear arteries and can be used to repair small central defects in the cribriform plate region. More laterally oriented forehead-scalp flaps based on the supraorbital or superficial temporal arteries have also been described.
    • Overall, the forehead-scalp flaps have limited application in current approaches to skull base reconstruction for a variety of reasons, including (1) limited surface area of tissue that can be mobilized, (2) relatively restrictive cutaneous bases that limit the mobility and reach of the flap, (3) difficulty in passing the thick pedicle through the cranial vault, (4) creation of a skin defect in a donor site within the surgical field, and (5) significant deformity at the donor site. With the advent of more reliable methods to transfer vascularized soft tissue, the forehead and scalp flaps are seldom used today.
  • Galeal-pericranial fascial flaps [4]
    • The deep scalp layers between the temporal lines can be dissected as vascularized membranes supplied by the supraorbital and supratrochlear arteries. These fascial layers are best used in repair of the anterior skull base. The pericranium provides a much more delicate layer of tissue, and its blood supply is somewhat questionable; however, harvesting of pericranial flaps carries virtually no donor site morbidity. The galea aponeurotica encloses the frontalis muscle anteriorly. The galeal-pericranial flap combines the galea aponeurotica and frontalis muscle layers with the underlying periosteum to create a much sturdier membrane with substantially improved blood flow.
    • Care should be taken when lifting this flap because violation of the subdermal fat and hair follicles can result in alopecia or scalp necrosis. Dissection of the flap in a way that leaves some fascia and muscle on the scalp side, effectively splitting the galea-frontalis layer, is advised. Galeal-pericranial flaps can be extended in length beyond the coronal scalp incision by dissecting posteriorly in a plane superficial to the desired layer before cutting down to bone.
  • Temporal flap system
    • The temporal region is the source for a variety of local flaps that can incorporate any combination of the temporoparietal fascia (superficial temporal fascia), the deep temporal fascia, the temporalis muscle, or parietal bone. The temporoparietal fascia is supplied by the superficial temporal artery and is confluent with the galea over the central scalp. This fascia is harvested by elevating immediately deep to the subdermal fat and hair follicles and (analogous to the galea-pericranial flap) carries a real risk of alopecia or scalp loss along the edges of the incision when large segments of fascia are elevated. When extended to its full limit at the cranial midline, the temporoparietal fascial flap can be rotated to seal dural defects in the depths of virtually all infratemporal-middle fossa or posterior fossa defects. Notably, the temporoparietal flap does not provide bulk to fill large soft tissue defects.
    • The temporalis muscle is supplied by the middle temporal arteries, which are branches of the superficial temporal arteries, and by the deep temporal arteries, which branch from the maxillary artery to enter the medial aspect of the muscle. Despite several early reports advocating its use for reconstruction of anterolateral, middle, and posterior fossa defects, many clinicians now realize that the temporalis muscle's usefulness is in fact quite limited. The major drawbacks of the temporalis muscle relate to its limited reach and mobility, compromised vascularity due to interruption of its blood supply during exposure of the skull base, and significant donor site deformity following its mobilization from the temporal fossa. In special situations, harvesting the muscle with segments of parietal calvaria in continuity with the overlying galea-pericranium as a composite pedicled flap may be desirable.
    • Septonasal mucosal flaps can occasionally be used to help seal defects in the roof of the nasal and ethmoid cavities. Unfortunately, the viable mucosa remaining after tumor removal often is greatly compromised, and these flaps are generally used during transnasal endoscopic approaches to remove very small tumors or when repairing CSF leaks.

Regional flaps

Regional flaps are tissues near the head and neck but not adjacent to the defect. These flaps are based on relatively long pedicles that allow the distal portion of the flap to reach into the defect, while the base remains attached to the donor site. Typically, regional flaps are musculocutaneous in design and consist of an island skin paddle overlying a major muscle through which perforating vessels pass to supply the skin. [5] Musculocutaneous flaps provide a large quantity of well-vascularized soft tissue. During the 1970s, musculocutaneous flaps revolutionized head and neck reconstruction following tumor ablation of the oral cavity and oropharynx. However, when applied to skull base reconstruction, these flaps are significantly limited in their ability to reach into the various defects, and tethering by the muscular pedicle restricts their mobility. [6]

  • Pectoralis major myocutaneous flap
    • The pectoralis major muscle can be used as a vascular pedicle to supply an island of skin overlying its lower insertions along the lower parasternal region of the chest. The flap is based on the pectoral branch of the thoracoacromial artery and requires that the whole muscle be dissected completely free of its attachments so that it can be rotated superiorly around the clavicle. Unfortunately, of all the regional flaps, the reach of the pectoralis major myocutaneous flap into the skull base is the most limited and, when tunneled under the neck skin, cannot reliably be used to close defects of the orbits or the paranasal sinuses involving the anterior skull base. In the lateral skull base, extension superior to the ear is difficult.
    • Other shortcomings include a very thick subcutaneous fat layer in patients who are obese and a relatively high incidence of partial skin loss at the distal end of the flap in cases with tension on the pedicle. Furthermore, loss of the pectoralis muscle considerably weakens the shoulder-upper arm functional unit and is especially problematic in patients undergoing simultaneous neck dissection with potential impairment of the trapezius muscle.
  • Lower trapezius flap: The trapezius muscle can be used to create flaps with a variety of designs, depending on the vascular supply included in the flap base. For skull base reconstruction, the inferiorly based trapezius island flap with blood supply from the dorsal scapular artery and vein is the most useful design because of its long arc of rotation. The overlying skin paddle can be placed low on the back, extending beyond the tip of the scapula. The skin paddle can be tailored to cover large cutaneous defects of the lateral skull base; it is much better suited to this task than the pectoralis flap. If no loss of skin has occurred, the flap can be deepithelialized to seal the dura and to provide bulk for contour restoration. Donor site morbidity is minimal when function of the rhomboid major and upper trapezius fibers is preserved. In addition, flap necrosis occurs if the dorsal scapular artery has been transected during concurrent or previous neck dissection.
  • Latissimus dorsi flap: The latissimus dorsi muscle is a broad fan-shaped muscle that can be used to carry a very large segment of overlying skin on a long arc of rotation across the axilla. This muscle receives its blood supply from the thoracodorsal artery and vein, which are branches off the subscapular vessels.
    • Dissection of the flap involves (1) transecting its origin from the spinous process, (2) completely elevating the muscle off the chest wall, (3) separating it from the serratus anterior muscle, and (4) cutting the tendinous insertion into the humerus.
    • The flap is then left attached only by its neurovascular pedicle and is passed through the axilla into the neck between the pectoralis muscles and over the clavicle.
    • When elevated to its fullest extent, the latissimus dorsi flap can reach into most skull base defects but is particularly well suited for repair of massive defects of the lateral cranial base following large skin resections, as happens with extensive parotid or external ear malignancy involving the auricle.

Revascularized free flaps

Revascularized free flaps are the most recent major advances in head and neck reconstruction. [7] These flaps are dissected in the same way as pedicled flaps, usually from sites distant to the defect. The vascular pedicle is divided, and the tissue is transferred to the defect. Blood supply is reconstituted as quickly as possible by microsurgically anastomosing the artery and vein of the flap's vascular pedicle to a suitable artery and vein at the recipient site. Free flaps have facilitated the ability to reconstruct the most complex of skull base defects that previously led to major complications.

  • Radial forearm flaps: Radial forearm flaps are based on the radial artery. Although bone harvest is an option, they are typically harvested as fasciocutaneous flaps to limit the significant donor site morbidity that results from including a portion of the radius. Advantages include a long vascular pedicle and ease of dissection. The biggest limitation is the relatively small surface area of skin available and the lack of sufficient bulk to restore extensive soft tissue defects. [8]
  • Rectus abdominis flaps
    • Rectus abdominis flaps are based on the deep inferior epigastric artery and vein and can be harvested as either a myogenous or a myofasciocutaneous flap. Early in the application of free revascularized flap reconstruction to skull base defects, the rectus abdominis flap became the workhorse free flap for anterior and middle cranial base reconstruction.
    • Advantages of the flap include (1) potential for a very large cutaneous skin paddle, (2) ease of harvest, (3) long vascular pedicle, and (4) versatility in allowing simultaneous work while tumor removal is completed.
    • Disadvantages include an overly bulky reconstruction when taken as a myocutaneous flap in individuals who are obese. Because of this problem, the rectus abdominis flap is often harvested as a muscle-only flap to restore lost bulk, with skin grafting used as necessary in cutaneous defects. When used in this fashion, the rectus flap undergoes considerable atrophy and is poor for long-term restoration of soft tissue contour.
  • Scapular/parascapular and latissimus free flaps
    • The subscapular artery and vein are branches from the middle third of the axillary vessels, which divide into the circumflex scapular and thoracodorsal vessels. The scapular/parascapular free flap is based on the circumflex scapular artery and can be harvested as either a fasciocutaneous flap of scapular/parascapular skin or as an osseomyocutaneous free flap, if the lateral scapular bone is included. The greatest advantage of subscapular system free flaps is their versatility in reconstructing complex, large, composite defects with missing bone, soft tissue, skin cover, and mucosal cover.
    • The scapular/parascapular free flap is based on the circumflex scapular artery and can be harvested as either a fasciocutaneous flap of scapular/parascapular skin or as an osteomyocutaneous free flap, if the lateral scapular bone is included. The greatest advantage of subscapular system free flaps is their versatility in reconstructing complex, large, composite defects with missing bone, soft tissue, skin cover, and mucosal cover.
    • Latissimus dorsi flaps are based on the thoracodorsal artery and can be harvested as either a myogenous or a myocutaneous flap. Advantages include a very large, relatively thin, and pliable cutaneous skin paddle in combination with a long vascular pedicle.
    • Drawbacks of the scapular/parascapular or latissimus flaps include the need for patient repositioning in order to harvest and significant donor site dysfunction when bone is harvested. In addition, the scapular/parascapular flaps have a relatively short vascular pedicle that often necessitates interpositional vein grafting to reach the recipient vessels.
    • By combining the scapular/parascapular and latissimus dorsi components, a so-called axillary megaflap can be harvested to repair massive head and neck defects.
  • Gastro-omental free flaps: These flaps can include either a segment of gastric mucosa in combination with omentum or omentum alone. Gastro-omental flaps are based on the gastroepiploic artery and veins.
    • The gastro-omental flap has several features that make it ideal for skull base reconstruction, and it may evolve into the free flap of choice in the future. Advantages include (1) a relatively long vascular pedicle; (2) excellent healing properties, which are particularly useful in an irradiated bed; and (3) the ability to restore soft tissue bulk with omental fat, which has predictable long-term volume characteristics and conforms to fit the complex 3-dimensional voids of skull base resections extremely well.
    • Gastric mucosa is a very good restoration for mucosal defects because it provides a moist, lubricated, nondesquamating lining.
    • Disadvantages are relatively minor and include the potential for peritoneal cavity and abdominal wall complications, delayed hemorrhage from the gastric mucosa ulceration, and excess gastric secretions.

Summary of options for skull base reconstruction

See the list below:

  • Grafts
    • Skin
    • Fascia
    • Fat or dermis-fat
    • Allografts - Dura, dermis, bone
  • Local flaps
    • Forehead and scalp flaps - Cutaneous
    • Galeal-pericranial - Fascial
    • Temporal system - Muscle, fascial, osseus
    • Septonasal - Mucosal
  • Regional flaps
    • Pectoralis major - Myocutaneous
    • Latissimus dorsi - Myocutaneous
    • Inferior trapezius - Myocutaneous
  • Revascularized free flaps
    • Radial forearm - Fasciocutaneous
    • Rectus abdominis - Myofasciocutaneous
    • Subscapular - Osseo/myofasciocutaneous
    • Latissimus dorsi - Myocutaneous
    • Gastro-omental - Fascial/mucosal
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Intraoperative Details

For a variety of reasons, skull base reconstruction should be performed on a primary basis at the time of tumor removal. In general, considerations in selection of the most appropriate technique for a skull base reconstruction can be grouped into the following categories: (1) dural repair, (2) soft tissue barrier, (3) osseous reconstruction, (4) surface defects in mucosal lining or skin cover, and (5) reconstruction of adjacent head and neck defects. These considerations are discussed in detail below for each skull base region.

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Approaches to skull base reconstruction

Anterior cranial base

See the list below:

  • Dural repair: Invariably, following extirpation of tumors involving the anterior cranial base, dural defects ensue that involve some part of the olfactory apparatus and potentially other areas, depending on the degree of dural resection necessary to obtain negative margins. Ideally, repair these defects using an autologous fascial graft of pericranium or temporalis fascia carefully cut to fill the defect and sewn to intact dura around the periphery to create watertight closure.
  • Soft tissue barrier
    • Anterior skull base resection frequently results in wide-open communication between the intracranial space, sinonasal cavities, and nasopharynx. Because of this communication, skull base reconstruction should include a vascularized soft tissue barrier to seal and protect the dura in most cases, especially when large areas of communication exist, a watertight dural closure is not possible, or in patients who have had radiation therapy.
    • The galeal-pericranial flap provides an ideal choice for such defects and has evolved into the workhorse flap for anterior skull base reconstruction. [4] This flap can cover wide areas of the anterior skull base and can reach posteriorly to the sphenoid sinus and upper clivus, if care is taken during the initial exposure to lengthen the flap posteriorly behind the scalp incision. If possible, secure the fascia with sutures to the deep margins of the bony defect, which can be further reinforced using resorbable collagen, fibrin glue, or nasal packing.
    • In certain situations, a free flap is the best option for establishing a soft tissue barrier along the anterior cranial base. [3, 7] These cases include (1) revision surgery in which the galeal-pericranial flap was harvested previously; (2) secondary reconstruction with loss of the frontal bone and gross intracranial infection; and (3) free flap reconstruction of adjacent facial structures such as the orbit, nose, or maxilla.
    • In previously irradiated patients, the galea-pericranial flap can be used for less extensive resections; consider free tissue transfer in more extensive defects or when the viability of the galea-pericranium is questionable. Several different free flaps can be used as a soft tissue barrier for the anterior skull base, including the radial forearm fasciocutaneous flap, the rectus abdominis myofascial flap, or the omental flap. Local forehead-scalp skin flaps provide inadequate coverage, although they may be adequate in very limited resections. Regional musculocutaneous flaps generally do not reach the anterior skull base and can only be inset into the cranial base when an accompanying adjacent facial defect of the frontal or orbitomaxillary region exists.
    • For very limited skull base defects, such as in the repair of CSF leaks through an extracranial approach or following removal of tumors with small areas of skull base involvement (1- to 2-cm defects), septonasal flaps provide a good option to seal the dural repair. Septonasal flaps are especially suitable for endoscopic skull base surgery. [9, 10, 11, 12]
  • Osseous reconstruction
    • This reconstruction of the anterior skull base begins with the design of the osteotomy segments during exposure. In general, place burr holes away from the forehead skin and limit them to the least number required. Frontal osteotomies typically have passed 1-2 cm above the supraorbital rims; but in many cases, these procedures can be accomplished in a subfrontal fashion, which places the inferior bone cuts in a nonvisible location and widens the access angle into the anterior cranial base, while decreasing the amount of frontal lobe retraction required to dissect into the sphenoclival region.
    • When inclusion of the nasal bones with the frontoorbital bone segment is desirable, preservation of a small rim of the inferior nasomaxillary bridge decreases the possibility of a step deformity at the upper lateral cartilage junction with the nasal bones. Pre-plate the osteotomized segments before full mobilization to facilitate anatomic repositioning during the reconstructive phase of the surgery.
    • Undertake calvarial repair for defects larger than 1-2 cm along any part of the cranium directly beneath the scalp to prevent indentation and contour deformities. This practice holds true along the frontal vault, parietal regions, and the superior or lateral orbital rims. Bone grafts are typically used for the orbital rims. Titanium mesh or bone substitutes are becoming increasingly popular to replace defects in the flat bones of the skull. [13] The orbital roof can be left unreconstructed unless the majority of it is resected, in which case consider repair so that pulsations from the frontal lobes are not transmitted to the globes, potentially causing visual disturbances and pulsatile exophthalmos. The osseous floor of the midline and central bony skull base (ie, cribriform plate, roof of the ethmoid labyrinth, planum sphenoidale, sphenoclival area) is not typically replaced with bone following removal.
    • In the past, neurosurgeons believed that bony reconstruction was necessary along voids in the skull base to prevent brain herniation, but except for extremely large defects, this is unnecessary provided a soft tissue barrier has been constructed and the dead space has been obliterated.
  • Mucosal/skin defects: In general, repair of mucosal defects of the anterior skull base does not require restoration with a comparable epithelium. Mucosalization of the vascularized soft tissue barrier used to seal the skull base defect occurs by migration from the remaining adjacent respiratory mucosa. This migration resurfaces the defect with a moist nondesquamating lining, which is preferable to reconstruction with a cutaneous flap, which sheds keratin, is prone to crusting, and can become malodorous. Defects in the skin cover following anterior cranial base resections typically accompany simultaneous removal of adjacent facial skin and usually are the result of cutaneous or sinonasal malignancy that has invaded the skull base. Repair in this scenario is best accomplished using a revascularized free flap.
  • Associated head and neck reconstruction: Defects occurring in combination with anterior skull base resections can be involved with loss of maxillofacial support and skin cover and soft tissue contents in the nose, orbits, and maxilla. Free flaps provide the ideal method of repair and can be used to simultaneously provide an excellent soft tissue barrier for the intracranial space. Options include fasciocutaneous flaps, such as the radial forearm or rectus abdominis and latissimus dorsi myocutaneous flap, which are useful to replace large areas of facial skin loss. The scapular and fibular osseomyofascial flaps can be used in cases in which restoration of skeletal support in addition to skin and soft tissue loss is desirable. Optimization of form and function often requires secondary placement of osseointegrated implants to retain customized facial or dental prosthesis.

Middle and central cranial base

See the list below:

  • Dural repair: The principle of achieving a watertight closure of dural defects, using autologous fascial patches when necessary, applies to the middle and central cranial base as well as the anterior skull base. Unfortunately, particularly when defects have occurred in the parasellar region, complete closure of the leaks may not be possible. In these situations, overlaying of a well-vascularized soft tissue barrier onto the dura is advisable.
  • Soft tissue barrier
    • A number of different options can be used for soft tissue closure of the middle/central cranial base, depending on extent of dural resection, status of its repair, degree of soft tissue loss, and whether the sinonasal tract or nasopharynx has been opened. In cases with intact dura or limited dural injury repaired with a watertight closure and no breach of the upper respiratory tract, small soft tissue defects can be restored most readily using abdominal fat grafts. Unfortunately, when fat grafts are used to obliterate larger defects, long-term atrophy leaves unacceptable contour defects.
    • In cases with extensive dural injury, a vascularized soft tissue barrier is advisable, particularly when the repair is not watertight. Options include the temporoparietal fascial flap when little to no accompanying loss of soft tissue bulk exists. Large soft tissue deficits are ideally restored with revascularized free flaps. Myogenous free flaps, such as the rectus abdominis or latissimus dorsi, undergo considerable atrophy over time because of deinnervation, and therefore, substantial overcorrection is necessary to restore adequate volume in the long term.
    • The omental free flap is much more predictable in restoring lost soft tissue bulk and affords an excellent material to seal the intracranial space. Of all available options, a rich vascular supply of the omentum, combined with its freedom of movement, imparts the omentum with the best 3-dimensional adaptability to safely fill complex skull base voids. When free flaps are not feasible, consideration can be given to pedicled regional flaps to provide a soft tissue barrier and bulk. Both the inferior trapezius and the latissimus flaps can be used, although the inferior trapezius has proven to be somewhat more reliable and versatile. Mucosal resection of the nasopharynx or sinonasal tract is an absolute indication for reconstruction using vascularized soft tissue to prevent salivary contamination of the dura and carotid artery. In this situation, free flaps are the only option to safely and reliably close the defect.
  • Osseous reconstruction: In general, bone loss encountered with approaches to the middle/central skull base does not result in problems. Osteotomies involving the lateral orbit, zygoma, frontoorbital, or squamous temporal region are pre-plated, and the segments can be returned to their anatomic position concurrent with closure. If these areas mandate removal because of tumor involvement or are lost because of necrosis or infection, consider bone grafts, hydroxyapatite bone substitutes, or titanium mesh. [14] Resection of the floor of the middle fossa is usually performed with drills and/or rongeurs, and replacement of this bone is unnecessary provided underlying voids have been obliterated with soft tissue reconstruction. When the glenoid fossa has been osteotomized and removed, take care to reposition it into its preexisting location because small changes in the position of the condylar head result in substantial occlusal shifts and mandibular dysfunction.
  • Mucosal/skin defects: Restoration of significant loss in mucosal surface can be achieved only with free flaps. Historically, the rectus abdominis free flap was used most often; however, long-term problems include cicatrization and stenosal scarring of the nasopharynx. The gastro-omental flap provides a better repair, with a lubricated mucosal surface less prone to shrinkage and distortion of the nasopharyngeal airway. Lost skin cover overlying the middle cranial base can be replaced with either free flaps or pedicled myocutaneous flaps, depending on other reconstructive requirements.
  • Adjacent head and neck reconstruction
    • Nearby structures that may require reconstruction include the lateral face, mandible, and auricle. Cheek skin can be replaced using local cervicofacial rotation flaps, pedicled myocutaneous flaps, or free flaps, depending on the other reconstructive concerns and nature of the defect. [15] Complete removal of the outer ear is best repaired using osseointegrated implants to retain a prosthetic auricle. Attempts to fabricate ears from adjacent tissues typically used for autologous auricular reconstruction are unsatisfactory because of the extensive violation of these tissues that accompanies skull base surgery.
    • The issue of mandibular reconstruction following skull base surgery remains controversial. Some authorities advocate not replacing condylar-ramal segments removed during exposure, citing greater degrees of trismus and deviation when reconstruction is undertaken; others prefer not to resect the condyle if at all possible during exposure but favor reconstruction of the ramus-condyle-temporomandibular joint in the occasional instance that resection is necessary for exposure or because of tumor involvement.

Posterior cranial base

See the list below:

  • Dural repair: Posterior cranial base surgery usually involves transmastoid, retrosigmoid, or suboccipital approaches to the cerebellopontine angle. Unfortunately, dural repairs along the adjacent brainstem are virtually impossible to perform in a watertight fashion. However, these procedures almost always target benign tumors and do not have accompanying loss of skin cover or mucosa of the respiratory tract. Despite the inability to completely repair the dura, most patients do well with an adequate soft tissue barrier to obliterate any dead space.
  • Soft tissue barrier: The majority of posterior cranial base tumors do not result in significant soft tissue deficits following resection. Fat grafts are commonly used as the only soft tissue barrier to obliterate the resection cavity. The temporoparietal fascial flap is a good local option when a vascularized soft tissue barrier is desirable.
  • Osseous reconstruction: Loss of the mastoid prominence is commonly associated with posterior cranial base surgery. Variable amounts of the occipital area may also be lost. In selected cases, removal of the mastoid prominence may be possible using an osteotomy technique and pre-plating so that it is returned to its anatomic position as a cortical shell during the reconstructive phase of the procedure. Large occipital defects that have been drilled away can be repaired with titanium mesh or hydroxyapatite bone substitutes, if they will cause visible deformity.
  • Mucosal/skin defects: Defects in skin cover or mucosal lining are very uncommon with posterior cranial base tumor resections. Defects in skin cover over the temporal region probably are the best situation in which reconstruction using pedicled flaps (eg, latissimus dorsi, inferior trapezius) can be used successfully.
  • Adjacent facial reconstruction: Uncommonly, loss of an auricle may necessitate reconstruction.
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Secondary cranial base reconstruction

Occasionally, repair of skull base defects may be necessary on a secondary basis. This situation most commonly is the result of wound healing complications following a major craniofacial–skull base procedure.

Indications

The most common indication for secondary reconstruction is a CSF leak that does not close with conservative management and lumbar drainage. Depending on size of the dural defect, extent of cranial base resection, and status of adjacent tissues, surgical management requires revision of the dural repair and introduction of a new vascularized soft tissue barrier. A free flap often is necessary to ensure an effective seal in cases with large defects widely open to the respiratory tract, particularly if the surgical field has been irradiated previously.

Another problem that can require secondary reconstruction in the anterior skull base is pneumocephalus with subsequent intracranial infection, bone necrosis, and loss of calvarial segments. This situation usually occurs following extensive anterior cranial base procedures and is primed by incomplete dural closure and inadequate soft tissue reconstruction in conjunction with the patient's ability to create significant positive nasopharyngeal pressure, which pushes air and secretions through the dura. Positive nasopharyngeal airway pressure occurs when the patient can swallow against obstructed nares or blows his nose. Repair of such defects requires extensive debridement of nonviable dura and bone, followed by a dural patch and introduction of a free flap to obliterate the dead space and to create a soft tissue barrier. Repairs use vascularized tissue as well as bony reconstruction, which is most readily accomplished using alloplastic titanium mesh and hydroxyapatite bone substitutes.

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Postoperative Details

In the early postoperative period, close monitoring of the viability of flaps used in skull base reconstruction is necessary. This is particularly important when revascularized free flaps have been used. If possible, a portion of the flap should be externalized to allow for periodic visual monitoring using color, turgor, capillary refill, and bleeding with pin-prick as indicators of perfusion status. When the free flap is completely buried, other methods of monitoring can be used such as Doppler assessment over the course of the vascular pedicle. More recently, buried Doppler probes placed directly on the flap vessels have become commonly used and provide the earliest detection of impending blood flow problems.

In addition, detecting any hematomas that may occur and compromise blood flow through the vascular pedicles is important. Immediate exploration and drainage of fluid collection is required. Cerebrospinal fluid leaks become apparent in the postoperative period as watery rhinorrhea, watery otorrhea, or a fluid collection. Suspicion of CSF within any fluid drainage can be evaluated using the clinical halo sign or laboratory tests to assess for glucose and protein in the drainage. Recently, assay of beta-2 transferrin has emerged as a foolproof diagnostic tool to evaluate possible CSF leaks.

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