Postoperative Imaging Appearance of Iliac Crest Free Flaps Used for Palatomaxillary Reconstructions

Conventional Imaging Appearance

On postoperative CT imaging, the osseous component of the ICFF appears as a thick sheet of bone with 2 cortical layers and a sclerotic trabecular surface. The bone has a hyperattenuated cortex and intermediate attenuation of the trabecular layer (Fig 4). The osseous component of the flap may be used to restore the normal osseous boundaries of the maxilla, alveolus, orbital rim, and pyriform aperture. The ilium is thickest at the spine and narrows posteriorly but appears on 2D imaging as a uniformly thick sheet of bone.¹⁷

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FIG 4.

Axial imaging of a normal ICFF demonstrating a thick sheet of bone with a hyperattenuated cortex and intermediate attenuation of the trabecular surface. An osteotomy site is demonstrated and filled with corticocancellous bone (arrow). Images were obtained in the immediate postoperative period. Left cheek prominence is an expected immediate postoperative finding in the flap setting. Normal cheek cosmesis will be obtained over time.

When the internal oblique muscle is used to obliterate the maxillary cavity, it is seen on imaging as opacification of the maxillary antrum.¹² Transposition of the internal oblique muscle through the defect creates a neopalate medial to the neoalveolar ridge formed by iliac bone. The muscular components of the flap will appear striated and thin.¹ McCarty et al¹ have reported that in the initial postoperative period, the muscular components of the flap may appear hypointense on T1-weighted images and hyperintense of T2-weighted images and enhance with gadolinium contrast. However, as the muscle atrophies and becomes more fatty, it will appear heterogeneous on both T1-weighted and T2-weighted images and more hypoattenuated on CT.¹⁸ Muscle denervation after flap harvest is believed to contribute to the increased enhancement of the muscular components of the flap over time.¹⁹ The muscular enhancement with gadolinium should not be mistaken for tumor recurrence.¹⁹ Sharp boundaries between the muscular components of the flap and nearby native structures generally indicate a benign process.⁷ Familiarity with flap maturation is important, specifically the tendency of the muscular portion of the flap to progress toward fatty atrophic changes, to avoid false identification of recurrent disease. The fatty components of the flap should contain no areas of nodularity or focal enhancement.¹

Contouring of the iliac bone can be accomplished by performing a unicortical osteotomy in the lateral surface and the iliac crest, which permits the bone to be “green stick fractured,” if a bend in the bone is required to accommodate to the normal architecture of the palatomaxillary complex. By creating this cut in this orientation, the DCIA and DCIV are preserved along the medial surface. The resulting “open osteotomy” is usually filled with corticocancellous bone chips that are harvested from the remaining iliac bone. Over time, this osteotomy will form solid bone. It should be noted that the goal of reconstruction is to place the neoalveolar maxillary ridge in direct apposition to the mandibular alveolus to facilitate dental restoration and normal occlusal relationships.

Osseointegrated dental implants are often inset into the ICFF (Figs 3 and 5).¹² Postoperative imaging evaluation is crucial for accurate monitoring of the angular position of the implants, their relationship with the adjacent bone, and the condition of the implants over time.²⁰ Periapical radiographs, panoramic radiographs, and CT imaging can all be used to evaluate dental implants.²¹ In particular, CT imaging can be used to evaluate bone-to-metal contact and identify any implant complications, such as hardware loosening.²²

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FIG 5.

Normal appearance of reconstructive plates and osseointegrated dental implants (arrow).

The ICFF also accommodates a mesh alloplast, which can be screwed to the anterior face of the iliac bone and lateral orbital rim to restore the orbital floor and reestablish a normal orbital volume (Figure 1B, -C). Imaging can be used to evaluate the position of these reconstructive techniques in the postoperative period and can also assess the orbital volume if there is any evidence of dystopia after disruption and reconstruction of the orbital floor. Any plates used in the procedure should appear level with both the new and native bone, and no lucency should be seen surrounding any screws (Fig 5).¹

Although the DCIA and ascending branches are important components of the flap, they are generally too small to be visible on standard diagnostic imaging but can be readily seen on CTA or MRA. The normal course of the DCIA and DCIV extends from the lingual surface of the iliac bone and passes either medial or lateral to the mandible to reach recipient vessels in the neck to revascularize the free flap.

Optimal Timing of Postoperative Imaging

The following postoperative imaging recommendations are based on author experience and may be approached more flexibly depending on individual institutional guidelines. Initial posttreatment imaging should be used to evaluate the appearance of the flap itself. Radiologists can ensure that no osteolysis nor bony erosion are present.¹ Initial posttreatment images can serve as a baseline to document any changes caused by treatment (both surgical and nonsurgical). These images can also provide a comparison for future examinations to better detect possible complications.²³ The CT portion of the examination should be used to evaluate the osseous borders of the flap for union, ensure that all fixation plates are still flush with the bone, and monitor for hardware lucency surrounding any inset screws.¹ Bridging new bone may be observed at the interface between the iliac bone and the native bone of the midface. Additionally, radiologists should re-examine preoperative scans in the postoperative setting to establish the extent and location of resection.¹ An understanding of both the preoperative and initial postoperative scans will assist in avoiding incorrect identification of recurrence on future imaging. For example, lymph nodes are sometimes transposed as part of the flap. This finding should be noted on baseline imaging to avoid falsely identifying such lymph nodes as recurrent disease on future imaging.

Approximately 12 weeks after treatment (either postsurgery or postradiation treatment), a PET/CT examination with contrast is recommended. This examination can be used to detect any persistent or recurrent tumor or metastases and to distinguish between treatment-related changes and new neoplastic changes.¹ The CT with contrast and the PET scan should be used in combination to evaluate the muscular portion and borders of the flap as a baseline. These scans will also improve the future detection of any recurrent, residual, or persistent disease.¹ MR imaging can be useful in detecting perineural invasion, intracranial extension, and cartilaginous involvement, among others.¹ As such, this imaging technique should be used in patients in whom there is a concern for risk for perineural invasion.⁷ Depending on a patient’s tumor type and surgical margin status, clinician familiarity with perineural extension of disease at the time of preoperative imaging interpretation is also recommended. Subsequently, surveillance imaging is recommended every 4 months for 2 years after surgery.⁷ The authors concede that the imaging intervals specified may not conform to the practice of all institutions.