4.3\ Temporal Fossa Implants

4.3.1\ Discussion

Soft tissue deficiency in the temporal fossa can produce cosmetic impairment and can result from the transposition of temporalis myofascial flaps and tumor debulking procedures, among

a

c

other surgeries. The contours of the temporal fossa can be augmented using implants, such as prefabricated porous high-density polyethylene (Fig. 4.3), silicone (Fig. 4.4), and methyl methacrylate (Fig. 4.5). The implants are usually inserted via a hemicoronal approach and can be secured using titanium screws to the underlying bone.

b

Fig. 4.3  Porous polyethylene temporal fossa implant. Axial CT image (a) shows a low-attenuation polyethylene implant with inner ridged surface positioned in the left temporal fossa (arrows). There is also left orbital exen-

teration. Axial T2-weighted (b) and axial T1-weighted (c) MR images in a different patient show a polyethylene implant in the right temporal fossa (arrows) with near-­ anatomic contours of the overlying scalp

4.4\ Mohs Micrographic Surgery

and Skin Grafting

4.4.1\ Discussion

Mohs micrographic surgery is a technique that enables skin neoplasms to be fully resected while maximizing preservation of normal tissues. Mohs surgery consists of removing the tumor via

sequential thin sections, which are concurrently examined under the microscope. The process is repeated until no remaining tumor is identified microscopically. When discernible on imaging, the defects characteristically appear as welldefined cavities in the skin and underlying soft tissues (Fig. 4.6). Large defects can be reconstructed using split-thickness skin grafts (Fig. 4.7), flaps, or synthetic materials such as AlloDerm.

Galeal flaps, such as the retroauricular rotation flap, can be used to cover scalp defects as large as 60% of the scalp surface area. Galeal flaps are comprised of fascia, subcutaneous tissue, and vascular components. In the early postoperative period, a remote donor site defect can be apparent, such as with “flip-flop” flaps (Fig. 4.8). Galeal flaps can incur essentially the same complications as other types of flaps, including infection, tumor recurrence, and necrosis, as well as dehiscence and alopecia.

Free flap transfer is used for repairing complex scalp defects in order to provide functional, cosmetic, and structural support when the use of skin grafts, locoregional flaps, and tissue expanders is not feasible. The latissimus dorsi myocutaneous flap is particularly useful for subtotal and total skull reconstruction, in which there is considerable dead space (Fig. 4.9). Latissimus dorsi flaps can be harvested with ribs (myo-osseocuta- neous) or combined with titanium mesh for added support. Omental flaps are another option for closing large scalp and cranium defects (Fig. 4.10). These contain mostly adipose tissues and are covered by skin grafts. Other donor tissues for free flap transfer include rectus abdominis muscle flaps, scapular flap, radial forearm flap, and anterolateral thigh flap. Vascular supply is typically obtained via anastomosis to the superficial temporal artery and vein or at times the occipital artery. Complications include delayed flap failure,­ which requires secondary reconstruction, neck hematoma, venous thrombosis, skull base infection, large wound dehiscence, small wound dehiscence, donor site hematoma and seroma, and cerebrospinal fluid leak.

Fig. 4.9  Latissimus dorsi muscle flap. The patient has a history of extensive squamous cell carcinoma of the scalp, with invasion of the calvarium. Axial CT image (a) shows titanium cranioplasty of the right occipital and parietal

regions and an overlying muscle flap. Characteristic muscle fibers are apparent in the flap on the axial T1-weighted MRI (b). Axial post-contrast Tl-weighted MRI (c) shows enhancement of at least some of the muscle fibers