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5 Cisternal Cerebrospinal Fluid Taps

Nora Ortinau

Introduction surface in lateral recumbency. The same procedure can be
Cerebrospinal fluid (CSF) analysis is an important part of a com- performed in sternal recumbency; however, this positioning usu-
plete neurological work‐up. However, while it is useful for limiting ally requires the sample to be drawn by suction into a syringe,
the differential diagnosis list when evaluated in conjunction with necessitating additional manipulation of the needle while in the
imaging results, it rarely yields a definitive diagnosis [1]. The clini- medullary cistern and may enhance the possibility of blood con-
cian should be familiar with the clinical indications for performing tamination. Typically the patient is placed in right lateral recum-
a CSF tap and the risks involved. In the appropriate patient, cisterna bency for right‐handed collectors, and left lateral if the collector is
magna puncture is a relatively straightforward procedure for left‐handed. The hair on the dorsal midline from approximately the
obtaining a sample of adequate size and quality to help form a com- external occipital protuberance to the spinous process of C2 is
plete clinical picture. Cisternal taps are also coupled with injections clipped and the area aseptically prepared.
of nonionic iodinated contrast agents for myelography. Only Proper patient position is of upmost importance in facilitating
approved agents for intrathecal are used for this purpose. the acquisition of CSF from the cisterna magna, and thus staff
Clinician familiarity with anatomical landmarks, sample han- should be familiar with how to position the patient. The patient’s
dling, and the supplies necessary to perform the tap is essential. The dorsum is positioned so it is even with the edge of the table. The
cisterna magna is located dorsal to the caudal brainstem between positioner should grasp the nose, extend the head and neck for-
the foramen magnum and C1 [2]. Important anatomical landmarks ward, and then flex the nose toward the chest, perpendicular to the
include the external occipital protuberance, the widest points of the axis of the spine (Figure 5.1). In large dogs it is often helpful if the
wings of the atlas, and the spinous process of C2 (Figure 5.1) [1,3]. positioner makes a fist, places it at the angle of the jaw, and then
In large or obese dogs, the spinous process of C2 may be very flexes the head around the fist (Figure 5.3), thus affording maxi-
difficult to palpate. mum opening of the cisternal space. The ears, if floppy, are held or
The cells in the fluid begin to degenerate within 30 min [1], and taped out of the way; often it is easiest to have the positioner hold
therefore it is also important to know where the samples will be the ears against the head. When the head is flexed, an imaginary
submitted and when they will be analyzed, as this will determine line is drawn sagittally along the midline and parallel to the table
the type of sample tube needed. The necessary supplies include (Figure 5.1B). At this juncture, the anesthetist makes sure the
sterile gloves, spinal needles, and sample tubes. Typically, a 22G 1.5‐ endotracheal tube is not kinked and the airway is maintained.
inch (3.8 cm) spinal needle with stylet is sufficient for most small
animal patients (Figure 5.2) [1]. In only the very large patient, a
longer spinal needle (2.5 inch, 6.35 cm) may be necessary; however, Sample Acquisition
the longer needles are more likely to deflect laterally and there may Once the patient has been properly prepared and positioned, the
be some loss of digital perception when performing the puncture. collector evaluates the positioning and is ready to obtain a CSF
sample. Sterile gloves are donned and the collector uses the thumb
and second finger of the left hand (if right‐handed) to palpate and
Patient Preparation and Positioning identify the widest point of the wings of the atlas. The dorsal mid-
The patient is intubated and in a surgical plane of anesthesia for line is identified by palpating the spinous process of C2 and the
sample acquisition. Anesthetic protocol is based on clinician prefer- occipital protuberance with the index finger of the left hand
ence and patient status, but should be chosen to have a minimum (Figure 5.4). The spinal needle is held like a dart and slowly inserted
effect on intracranial pressure. The patient is placed on a flat stable through the skin at a point just cranial to the intersection of an

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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