4.15\ Box Osteotomy

Hypertelorism can be corrected by performing box osteotomy, which involves creating a frontal

bone flap to help remove excess interorbital bone and to mobilize the orbits. Once the orbits are repositioned closer to one another, they can be secured with plates and screws (Fig. 4.39).

4.16\ Absorbable Hemostatic

Agents

4.16.1\ Discussion

Several types of topical absorbable hemostatic agents are available for neurosurgical procedures, including cellulose-, gelatin-, and collagen-based agents and thrombin and fibrin glue.

Oxidized regenerated cellulose, such as Surgicel, is available in the form of a fabric that can be used to line the margins of resection cavities or packed tightly to control a more focal source of bleeding. Implanted oxidized cellulose has been reported to mimic abscesses and masses on postoperative imaging. On CT, oxidized cellulose often displays low attenuation, and on MRI, it usually shows low signal on T2, but variable T1 signal (Fig. 4.40). Sometimes, the presence of high T1 signal can potentially mimic residual tumor on contrast-enhanced images. The hemostatic agent ultimately resorbs over the course of months.

Gelatin hemostatic agents, such as Surgifoam and Gelfoam, are available in powder or sponge form. On CT, the sponge usually displays air attenuation during the early postoperative period, but becomes higher attenuation as it absorbs cerebrospinal fluid/blood, resulting in high T2 and low T1 signal on MRI (Fig. 4.41), for example. Eventually, the sponge resorbs and is no longer apparent on imaging. Although gelatin foam hemostasis may incite varying degrees of granulomatous reaction, complications related to the use of these agents are unusual.

Gelatin-thrombin matrix (Floseal) functions as a sealant that acts at the end stage of the coag-

ulation cascade. The material has a rather characteristic appearance of a pseudomass with relatively low signal speckles in a background of hyperintensity on T2-weighted MRI (Fig. 4.42), when clusters have formed with fluid absorbed by the granules and retained in the matrix. These microbubbles and clot formation in the matrix cause magnetic field inhomogeneity with T2* effects evident by blooming susceptibility of the gelatin-thrombin matrix in the surgical cavity.

Neurosurgical procedures can involve a great degree of complexity and occur over extended periods of time, and the contents of the surgical cavity can be obscured by blood products. These circumstances can make it difficult for the neurosurgeon to visually identify surgical paraphernalia left within the surgical field. However, radiopaque markers can help to localize a retained sponge or instrument with imaging when the surgical count is not reached. For example, cottonoids are compressed rayon cotton pledgets or strips used for hemostasis, soft tissue protection, and tissue dissection that contain radiographically detectable markers (Fig. 4.43). Typically, cottonoids are not thrown off the field into a kick bucket when soiled as are other larger sponges. Rather, they are kept on the sterile field or discarded in a separate area to prevent them from being picked up with larger sponges leading to incorrect counts. Radiographs with at least two orthogonal views are usually sufficient for localizing retained surgical paraphernalia. Nevertheless, when other metallic implants are intentionally present, the task can be more difficult, and CT may be useful.

Fig. 4.40  Oxidized regenerated cellulose. (a) Axial CT image obtained after recent surgery shows globular low-­ attenuation material with the right frontal lobe surgical cavity (arrow). The Surgicel (arrows) has relatively low

signal on T2-weighted (b), T1-weighted (c), and SWI (d) sequences. Photograph of Surgicel (e) (Courtesy of Patricia Smith and Sarah Paengatelli)

Fig. 4.41  Gelatin foam. Axial CT image shows a folded sheet of Gelfoam (arrow) deep to the craniotomy, which has higher attenuation than the surrounding pneumocephalus but lower attenuation than the surrounding fluid. Axial T2-weighted (b) and T1-weighted (c) MR images

about 1 month after surgery show the hemostatic agent between the duraplasty and cranioplasty (arrows). Photograph of Surgifoam (d) (Courtesy of Patricia Smith and Sarah Paengatelli)

Fig. 4.42  Gelatin-thrombin matrix. Axial T2-weighed (a), T1-weighted (b), and SWI (c) MR images show a somewhat foamy appearance of the clustered hemostatic

agent within the deep right cerebral (arrows), which has developed blood clots

Fig. 4.43  Retained cottonoid. Immediately following resection of a large frontal meningioma, the neurosurgeons informed the radiologist that cottonoids were left behind. Postoperative frontal radiograph (a) and CT

in soft tissue (b) and bone (c) windows show the linear metallic structures associated with the cottonoids left the surgical bed (arrows) (Courtesy of Shehanaz Ellika MD). Photograph of cottonoids (d) (Courtesy Jene Bohannon)