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110 Section II: Intracranial Procedures

A B

Figure 11.2 A massive depressed skull fracture of the right frontal and parietal bones in a 3‐month‐old Yorkshire Terrier caused by a bite wound to the head.
(A) Preoperative and (B) postoperative three‐dimensional reconstruction of the CT scan. The areas within the circle represent the location of the depressed
segment.

(Figure 11.4A). The subcutaneous tissue is undermined and and not through the full thickness of the bone. After ensuring the ros-
reflected ventrally; however, subcutaneous dissection at the cranial tral, dorsal, and caudal connections are complete, a periosteal elevator
aspect of the incision is limited so the branch of the auriculopalpe- is carefully inserted under the flap and above the dura to pry the flap,
bral nerve is avoided, so this tissue is not cut but can be reflected breaking through the groove placed in the ventral aspect of the flap
ventrally with the temporalis muscle. (Figure 11.7A). If the craniotome with a dura guard is used, this ven-
The temporalis muscle is incised in a similar horseshoe fashion tral aspect is cut in similar fashion to the rest of the flap.
using an electroscalpel. The incision can extend rostrally to the bor- As the bone flap becomes loose, the surgeon tries to elevate any
der of the skin incision, to a point 2–4 mm lateral to its attachment dural attachments as the bone is slowly removed. If this is not done,
to the skull, and caudally behind the ear as needed for exposure. A the underlying dura can tear and sometimes result in considerable
periosteal elevator is used to undermine the temporalis muscle. The hemorrhage from the middle meningeal artery and its branches.
author prefers a rounded, wide‐blade, wooden‐handled periosteal Bipolar cautery is used to control this and any hemorrhage from the
elevator in large dogs and a Freer elevator‐dissector in small dogs bone is controlled with a coating of bone wax.
and cats. As the muscle is elevated, it is reflected ventrally If necessary, the craniectomy can be extended using Lempert or
(Figure 11.4B); the inner surface of the muscle is kept moistened Kerrison rongeurs to accommodate exposure of the lesion.
throughout the procedure with frequent bathing in warm saline. The exposed dura is inspected and the surgeon prepares to open
Reflection of the muscle exposes portions of the frontal, parietal, it and create a flap (Figure 11.7B). A number 12 blade is used to
temporal, and sphenoid bones (Figure 11.5). Location of the make the initial opening, then the edge of the dura is grasped with
craniectomy is determined by the location of the lesion and jeweler’s forceps and scissors (tenotomy, Potts) are used to complete
the reason for the surgery. Less invasive procedures (placement of the flap (Figure 11.8). The dural incisions are made along the dor-
ventriculoperitoneal shunt, marsupialization of the ventricle, evacu- sal, rostral, and caudal edges of the opening after ligating or cauter-
ation of blood clots, skull fracture elevations) may require only one izing the middle meningeal artery as ventrally as possible. Two long
or two burr‐holes. Removal of intracranial tumors, of course, does 5‐0 synthetic absorbable stay sutures are placed on the rostral and
require a considerably larger opening. The borders of the craniec- caudal corners of the dura and clamped with small hemostats before
tomy are determined in preoperative planning. Usually, four burr‐ reflecting it ventrally over the exposed reflected muscle tissue.
holes are made, one at each corner of the boundaries, using a All exposed tissues, and most especially the cortical surface, are
perforator or a high‐speed nitrogen‐powered drill with a rounded kept moist throughout the procedure with warm sterile saline solu-
bit (Figure 11.6). The burr‐holes should penetrate the inner cortical tion. If the surgeon chooses to replace the bone flap at the end of the
bone but optimally not damage the dura. Each burr‐hole is inspected procedure, it is kept in a moistened wrap of sterile gauze sponges.
with a small probe to ensure the inner cortical layer is perforated. Extraaxial lesions, such as meningiomas, may be visible from the
The four completed burr‐holes are connected to complete the bone surface; however, this is often not the case. Based on the preopera-
flap using a small burr with the high‐speed nitrogen‐powered drill or tive planning and the advanced imaging, the approximate locale of
a craniotome, preferably with a pediatric dura guard. The dorsal, ros- the lesion (tumor) is determined. A far better method of visualizing
tral, and caudal connections are made. If the drill is used, the span of intraaxial and extraaxial masses is with the use of intraoperative
bone between the ventral burr‐holes is connected, but only grooved ultrasound. This is a very useful tool and the process/technique has