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Chapter 12: Suboccipital Craniectomy/Foramen Magnum Decompression 117

Figure 12.5 Sagittal T2‐weighted MRI of canine patient with Chiari‐like
malformation changes (cerebellar herniation and syringomyelia). Figure 12.7 Patient positioning for suboccipital craniectomy/foramen mag-
num decompression. Note the additional area surgically prepared (inset)
over the dorsal aspect of the wing of the ilium for harvesting a fat graft.

Occipital
protuberance

C2 Spinous
process

Figure 12.8 Intraoperative photo showing dissection through the superfi-
cial cervical musculature with an incision extending caudally from rostral to
the occipital protuberance to the caudal aspect of the C2 spinous process.

Figure 12.6 Illustration showing caudal aspect of the canine skull. The area occipital dysplasia and the muscles lie just dorsal to a thin periosteal
encompassed by the dotted lines represents the area removed for most sub- membrane or simply directly overlie the dural membrane
occipital craniectomy/foramen magnum decompression procedures. (Figure 12.9). Vigorous dissection in these instances can cause
severe damage to the cerebellum.
Gelpi or other self‐retaining retractors are placed at the cranial
and caudal aspects of the exposure. Hemostasis is achieved with
along the midline through the biventer cervicis muscles and rectus monopolar or bipolar electrocautery. The exposed tissues are peri-
capitis dorsalis (Figure 12.8) [2–5]. The cranial attachment of the odically lavaged with warmed sterile saline solution.
nuchal ligament can be palpated as it attaches to C2 and the occipi- At this juncture, the surgeon inspects the area to ensure ade-
tal protuberance is exposed. A Freer periosteal elevator is used to quate exposure for the procedure. For intracranial tumor
elevate the musculature from the occipital bone, the dorsal arch of removal, the dissection can be carried laterally and dorsally to
C1, and the spinous process of C2. Frequently, the various muscle the nuchal line and occipital protuberance, respectively. The
arterial and venous branches are encountered and can produce con- occipital condyles are the ventrolateral extent of the dissection
siderable hemorrhage. At some juncture, branches of the great and the foramen magnum is the ventrocaudal extent. Often,
auricular artery are breached on both sides and require bipolar cau- slightly less lateral exposure is used for FMD procedures in the
tery to control [4,5]. surgical treatment of Chiari‐like syndrome. The dorsal atlanto-
The surgeon must carefully evaluate the structure of each patient’s axial membrane spans the gap between the caudal ventral extent
occipital bone before beginning periosteal elevation of the muscles. of the occipital bone and the dorsal arch of C1. This membrane
Some patients, especially the smaller breeds, will have extensive is fibrous and usually thickened in patients with Chiari‐like