• History of prior nasal or sinus surgery may compromise flap harvesting and selection of tissue for skull base reconstruction.
• Previous sphenoid surgery may have compromised the posterior septal branch of the sphenopalatine artery, the primary blood supply to the nasoseptal flap.
• Note prior or planned radiation therapy as this will affect healing and the choice of repair.
Perform a Detailed Endoscopic Exam
• Note evidence of prior sinonasal surgery, septal perforations, loss of turbinate/septal tissue, wide sphenoidotomy, and presence of septal deviation.
• Perform a pedicle assessment if there is a mass or has been previous surgery in the area.
• Check that endoscopic visualization of the potential defect will be possible to permit full closure.
• Note the potential geometry of the skull base defect that will result after resection.
1. Angles of the skull base surface may make placement of a graft more difficult and require longer flaps.
• Ensure adequate septal mucosal flap area in patients being considered for rotational septal flap repair.
1. Younger patients have a relative shortness of the nasal septum compared to the skull base.
• An important clinical rule is that coverage of two contiguous skull base areas is possible but not coverage of three.
1. Units are the clivus, sella/planum, cribriform, and frontal sinus.
• A defect in the coronal plane, if it extends lateral to the pterygoid, usually requires sacrifice of the ipsilateral maxillary artery and, therefore, a contralateral pedicled flap is necessary.
• Raising any pedicled flap should occur early in the procedure to ensure that vascular supply to the flap remains intact and facilitates speed of reconstruction once the lesion has been removed.
2. The flap can be stored in the ipsilateral maxillary sinus or nasopharynx for protection.
• Any pedicled mucosal flap should be designed as oversized for the defect because flap length is lost when contouring the flap to the skull base defect, and the flap usually will contract slightly as it heals.
• The flap pedicle may cause functional problems in the nose. It may be necessary to skeletonize the pedicle fully to ensure minimal mucosal trapping postoperatively and that no sinus is fully obstructed.
• Functional nasal mucosa from grafts or flaps should not be buried under any graft or intracranially to prevent mucocele formation.
• The most common points of failure of flap repairs are the dependent parts due to pressure and the most superior parts because of the danger of flap migration.
• Consider a Draf III frontal sinusotomy for frontoethmoidal skull base defects to facilitate flap placement, ensure a functioning frontal cavity, and allow for direct access for tumor surveillance.
• The majority of small defects <1 cm in the anterior skull base can be repaired using single-layer free grafts.
1. Rates of success are higher than 90%, but in high-flow leak situations success rates are much lower at 50% to 70%.
2. The differences between various methods and materials are minimal.
• Popular due to availability, biocompatibility, negligible costs, and rapid incorporation into the surrounding tissue
Fat
• Loss of 50% of its volume over time
• Unsuitable for an infected cavity
• Typically used in a plug fashion to fill intracranial dead space or the skull base defect
• Should not be used as a single repair modality but rather should be used in conjunction with an additional graft
Fascia
• Harvest sites include temporalis fascia and fascia lata
• Fascia lata has characteristics similar to dura, whereas temporalis fascia is thinner
• May be placed as an underlay between dura and skull base or as an overlay in the sinus cavity
• Best used as adjuvants to vascularized flaps rather than as alternatives
Bone/Cartilage
• Harvest sites include the vomer and septal cartilage, conchal cartilage, split calvarial grafts, rib and iliac crest.
• Used in underlay fashion as part of a multilayer repair with additional layer covering the bone/cartilage graft
• Bone/cartilage may be considered to prevent herniation of intracranial contents such as in the sella after pituitary surgery; however, indications for rigid support are controversial, and bony defect reconstruction is not always required.
• Disadvantages include risk of sequestra with large rigid grafts and poor tissue healing
• Readily harvested from the nasal septum floor or turbinates
• Inking the mucosal surface of graft with surgical marker prior to harvest may facilitate correct mucosal placement with glandular mucus-secreting side directed toward the nasal cavity.
• Graft contracts by nearly 20% during the healing process, which can lead to repair failure if the edges of the graft are not integrated into the surrounding mucosa when the contraction occurs.
• Engineered collagen products (eg, Biodesign® from Cook Medical, Bloomington IN; DuraMatrix® from Stryker, Portage, MI)
1. Can be used alone for reconstruction of small to large defects as single layer or in conjunction with pedicled or free mucosal overlays for larger defects
2. Consist of collagen-rich animal tissues that have been processed to remove all cells and antigens; optimized to encourage fibroblast in-growth, angiogenesis, and new collagen formation
3. All mucosa must be removed from the bone onto which the onlay is placed and adequate boney or dural edges must be available for inlay to permit direct contact required for revascularization.
4. Advantages include no need for graft/flap harvesting, good tissue handling characteristics during graft placement, readily available commercially, and avoids the need for prepping an additional surgical field.
5. Disadvantages include cost, potential risk of infection and some degree of inflammatory response to the non-autologous tissue, and may theoretically act as epileptogenic foci.
• Acellular human dermis (AlloDerm® from LifeCell Corporation, Branchburg, NJ)
1. Described for use in skull base reconstruction as single layer
2. Disadvantages include significant rate of postoperative crusting and local infections; theoretical risk of prion-mediated diseases
• Tissue glues (eg: Tisseel, Baxter, Deerflield, IL; DuraSeal, Covidien, Irvine, CA)
1. Used to hold final layer in place during postoperative period.
2. Use of these materials is not always required; limited evidence pertaining to endoscopic skull base reconstruction is available.
3. Glues may not provide added benefit to repair.
LOCAL PEDICLED FLAPS (Table 41–2)
• Repair method of choice for large defects >3 cm, and high flow CSF leaks, patients with prior radiation, or history of poor local wound healing
• Defect location and complexity guide vascularized flap choice.
• Nasoseptal flap is a mainstay in skull base reconstruction, but when unavailable anterior/sellar defects can be managed by anteriorly pedicled flaps or an endoscopically harvested pericranial flap, and clival/posterior defects can be reconstructed with an inferior turbinate or temporoparietal flap.
• Onlay vascularized flaps can be used when bony or dural edges are limited to allow for inlay grafts.
Nasoseptal Flap (aka Hadad-Bassagasteguy Flap)
• Advantages of the nasoseptal flap include consistent vascularity, long and robust pedicle, ease of harvesting, and the ability to customize its size and shape.
1. Can cover defects encompassing up to 50% of the anterior skull base and span from orbit to orbit
• Disadvantages include postoperative crusting from donor site on the exposed septal cartilage, decreased olfaction, and limited reach anteriorly in the frontal sinus.
• Overall success rate >95%
• A technical learning curve exists, however, with the first 25 patients reconstructed in one series having a 24% leak rate, whereas the last 200 patients had a leak rate of 4%, according to an article by Patel et al on endoscopic skull base reconstructive options and limitations.
• Preoperative planning is required to avoid sacrificing the nasoseptal flap during resection.
1. Technique may be unavailable due to tumor involvement of the septum, in cases with a septal perforation, or when previous sphenoidotomies have compromised the flap vasculature.
• In the pediatric population <10 years old, the nasoseptal area is often significantly smaller than the age-corresponding skull base defect because cranial growth occurs earlier in life, meanwhile septal growth is not complete until puberty when midface growth accelerates.
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