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86 Section I: Diagnostics and Planning

the mamillary processes of caudally lying lumbar vertebrae to later-
ally on the ends of the spinous processes of a vertebra lying two
segments cranially, immediately beneath the supraspinous liga-
ment. The lumbar portion of the interspinales muscle is covered by
the multifidus, running between contiguous edges of spinous
processes.
With regard to ligaments of the caudal lumbar spine, three are
described: from dorsal to ventral, the supraspinous, the inters-
pinous, and the ligamentum flavum (interarcuate or yellow) [4]. In
the dog and cat, as compared to humans, the supraspinous in the
lumbar spine is imperceptible and the interspinous ligaments are
poorly developed except dorsally, perhaps because of the major
degree of flexion of the lumbar spine exhibited by dogs and cats [7].
The weak interspinous ligaments, interspersed with muscle bundles
of the musculus interspinalis, connect adjacent vertebral spines.
Ventrally to the interspinous ligament lies a much more consistent
ligamentum flavum or interarcuate (yellow) ligament, consisting of
connective tissue between the arches of each adjacent vertebra. Figure 8.1 Aseptically prepared skin area for a lumbar tap.
Because of its consistency, a “popping” can sometimes be noticed
when the spinal needle perforates this ligament. Ventral to the fla-
vum ligament lies the epidural space in the vertebral canal, which keratinized cells and iatrogenic intraspinal epidermoid tumors [8].
separates the ligaments and the vertebral arches from the dura cov- In humans, 40% of intraspinal epidermoid tumors are considered a
ering the spinal cord. The caudal lumbar dural sac and subarach- late complication of lumbar puncture and associated with using
noid space (lumbar cistern), where CSF collection and intrathecal nonstylet needles [9].
injection of substances is performed, extend approximately 2 cm In humans, the incidence of headache after lumbar puncture is
beyond the end of the spinal cord, approximately at the level of the related to the diameter of the needle: smaller needle sizes (smaller
L6–L7 intervertebral disc in large and medium‐sized dogs and at hole in the dura) are associated with reduced frequency of headache
the lumbosacral junction in small‐breed dogs and cats [4]. A pair of [10]. Use of atraumatic (pencil‐point) spinal needles instead of the
valveless internal vertebral venous plexuses are located on the floor conventional “cutting” needle also reduces this risk [11]. Obviously,
of the vertebral canal, decreasing in size caudal to the level of the this complication is difficult to prove in veterinary patients. On the
fourth or fifth lumbar vertebra. other hand, the narrower (22G) longer needles (2.5–3.0 inch) are
more flexible and more difficult to place. In most large dogs, it is
necessary to use 20G needles to reduce needle bending. Most
Procedure smaller dogs require only a 22G 1.5‐inch needle.
Technically, lumbar taps are more difficult to perform than cerebel-
lomedullary cistern puncture, and are more likely to result in Position
iatrogenic blood contamination. A successful lumbar puncture Correct patient positioning is key to a successful tap. The author
technique requires practice. Using a lumbar spine skeleton prefers to position the patient in right lateral recumbency with the
model for constant referral to anatomical structures is helpful. clipped lumbar area away from the operator, and maintaining the
Fluoroscopy guidance simplifies accurate needle placement but is pelvic limbs in neutral position with a pad between the limbs to
not essential. As previously mentioned, lumbar puncture is per- keep them as parallel as possible (Figure 8.2). If the operator is left‐
formed at L5–L6 or L4–L5 in dogs, while a more caudal L6–L7 or handed, left lateral recumbency is preferred. The operator is then
lumbosacral space can be attempted in cats. Lumbar puncture in facing the ventral abdomen of the patient and needs to bend over
small animals requires general anesthesia in order to prevent move- the animal to insert the needle (Figure 8.3). It is extremely impor-
ment while proceeding. tant to keep the lumbar spine of the patient as straight and parallel
to the table as possible. This keeps the midline of the caudal lumbar
Preparation and Equipment spine more parallel to the insertion of the needle; otherwise the
A sufficiently large area of surrounding skin should be shaved needle could be inserted in an excessively lateralized angle away
(from around L4 to L7 with the midline centered on the spinous from the desired interarcuate foramen. Proper positioning can be
processes) and cleaned with an aseptic solution (Figure 8.1). The further accomplished by placing small pads or towels under the
operator performs a surgical scrub and dons sterile gloves. lumbar spine and under the ventral abdomen, and confirmed
Equipment required for a lumbar tap includes: through lateral survey radiographs or fluoroscopy, aiming for over-
• hair clippers; lapping of bilateral spinal anatomical components (ribs, lumbar
• sterile surgical gloves; transverse processes, wings of the ilium).
• spinal needle 20–22 gauge, 1.5–3.5 inch (3.8–8.9 cm), depending The patient can be positioned in sternal recumbency instead of
on the size of the patient; lateral. The sternal position prevents the spine being excessively
• sterile glass tubes free of anticoagulant for CSF collection. rotated, tilted or laterally flexed, as it can be in the case of lateral
Use of a stylet in the needle is considered essential, not only to recumbency. However, the lateral recumbency position is more
decrease the risk of promoting an infection in the vertebral canal, but comfortable for the operator and the whole procedure, particularly
to avoid introduction of epidermal fragments into the subarach- if sequential images are obtained over time during a myelographic
noid space, potentially resulting in implantation of desquamated study to assess the progression of the contrast. Some clinicians