Ultrasound‐guided atlanto‐occipital puncture for cerebrospinal fluid analysis on the standing horse

Abstract

The atlanto-occipital site (AO) is convenient for retrieving an adequate volume and quality of cerebrospinal fluid (CSF) in the diagnosis of neurological disease in horses. However, general anaesthesia is not always possible for horses displaying severe neurological signs, or for economical reasons. The objectives of the present work were to determine the feasibility and safety of ultrasound-guided CSF puncture at the AO site on the standing horse. Seven horses (six healthy and one mildly ataxic) were sedated with acepromazine (0.02 mg/kg bodyweight intravenously or 0.04 mg/kg bodyweight intramuscularly) and detomidine (0.01 mg/kg bodyweight intravenously), and placed in stocks or in a recovery stall with the head kept on a headstand. Puncture was performed by ultrasonographic guidance with a parasagittal technique, as previously described, using a 20 g, 3.5 inch spinal needle. In all horses, no adverse reaction was observed when crossing the dura mater and 20 ml of CSF was rapidly retrieved without any blood contamination. Ultrasound-guided CSF puncture can be performed easily at the AO site on a healthy standing horse. Regarding the potential risk of this procedure, safety measures and close observation are essential. Further studies on a larger amount of ataxic horses are also required before considering this technique as an alternative option for CSF puncture.

Ultrasonographic Examination of the Spinal Cord and Collection of Cerebrospinal Fluid from the Atlanto-Occipital Space in Cattle

“…All but one sample were clear and colourless and all had no or minimal microscopic evidence of blood contamination. Compared with samples from horses, the erythrocyte count of CSF samples was higher [15,16] or similar [17] in the cattle of the present study, but smaller than in samples collected using blind puncture without ultrasonographic guidance [8,9]. A minimum erythrocyte count of about 2000 to 3000 cells/μl is required to render a CSF sample grossly discoloured or turbid [10,11,22], and blood contamination often goes macroscopically unnoticed [9,11,12].…”

Ultrasonographic examination of the spinal cord and collection of cerebrospinal fluid from the atlanto-occipital space in cattle

“…In longitudinal section, the spinal cord appeared as a hypoechoic band characterised by the hyperechoic central canal and the hyperechoic pia mater visible on the dorsal and ventral surfaces. It was circular in cross-section, and the internal structure was partially heterogeneous in both planes as described in the horse [ 15 , 16 , 18 ]. The subarachnoid space surrounding the spinal cord was anechoic to hypoechoic, had a heterogeneous internal structure and was bordered by the hyperechoic pia mater and the hyperechoic arachnoidea and dura mater, but the latter two structures could not be differentiated.…”

“…The internal structure of the subarachnoid space appeared heterogeneous in both planes in the cows of the present study. The mean height of the subarachnoid space dorsal and ventral to the spinal cord was 8.9 mm and 8.4 mm, compared with about 1.5 cm for the dorsal section in the standing horses [ 16 ]. This difference may relate to the larger body size of horses compared with cattle.…”

“…A complication was reported in horses when the angle between the needle and dura was small, which resulted in the needle pushing the dura mater ventrally, instead of perforating it [ 15 ]. This complication is referred to as tenting phenomenon and has been described in human beings [ 21 ] and in another study on horses [ 16 ]; however, these authors did not feel that the angle of the needle relative to the dura mater was the cause. The tenting phenomenon increases the risk of accidental puncture of the spinal cord, but was avoided in horses by using ultrasonographic guidance [ 15 ].…”

“…In the second technique, puncture of the subarachnoid space is achieved through a parasagittal oblique plane while monitoring a parasagittal oblique image. These techniques have also been used in the standing sedated horse [ 16 ]. Another study described collection of CSF between the first two cervical vertebrae using a parasagittal approach while observing the spinal cord on a cross-sectional image in the standing horse [ 17 ].…”