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12 Suboccipital Craniectomy/Foramen

Magnum Decompression

Erin Y. Akin and Andy Shores

Indications
This procedure was first described by Oliver [1], and while the indications for
foramen magnum decompression (FMD) have changed, the basic
procedure has stayed much the same [2–5]. The procedure is used to
expose the caudal cerebellum, dorsal aspect of the caudal medulla, and
the most cranial aspect of the cervical spinal cord [2,4]. Indications for
suboccipital decompression and FMD include the following.
1 Neoplasms involving structures of the caudal fossa:
a cerebellum, dorsal aspect of caudal brainstem;
b cranial cervical spinal cord (Figures 12.1, 12.2 and 12.3).
2 Quadrigeminal diverticula (Figure 12.4).
3 Chiari‐like malformation (Figure 12.5).
4 Cerebellar biopsy.

Surgical Anatomy
An illustration of the caudal aspect of the canine skull is shown in
Figure 12.6. The cervicoauricular–occipital complex comprises the
superficial muscles encountered on the dorsal midline. Cranial to
the C3 vertebra the deeper dorsal cervical muscles include the clei-
docervicalis, sterno‐occipitalis, sternomastoideus, rhomoboideus,
splenius, semispinalis capitis biventer, and complexus. All these
make some attachment to the occipital bone and are reflected dur-
ing the dissection process [2,6].
In addition to the numerous arteries and veins associated with
the muscle attachments, the muscular and occipital branches of the
great auricular artery represent the vessels most commonly encoun- Figure 12.1 Transverse T1‐weighted postcontrast MRI of choroid plexus
tered. At least one of these branches also anastomoses with the tumor.
ascending branch of the omocervical artery [6].
The nuchal ligament attaches to the spinous process of the axis. Patient Positioning
The cranial aspect of the axis is the origin of the dorsal atlantoaxial The patient is placed in sternal recumbency on the operating table,
ligament that attaches to the dorsal arch of the atlas. Surgical anat- with the head ventroflexed perpendicular to the axis of the spine
omy for the cat is very similar; however, the nuchal ligament does (Figure 12.7). The positioning is similar to that used for a patient
not exist in this species. undergoing a cisternal spinal tap in dorsal recumbency, with the

Current Techniques in Canine and Feline Neurosurgery, First Edition. Edited by Andy Shores and Brigitte A. Brisson.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/shores/neurosurgery

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