EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2018
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CT Preparation Anaesthesia was induced with i.v. diazepam (Diazepam injection BP)4 at a dose of 0.05 mg/kg bwt and i.v. ketamine (Narketan 10)5 at a dose of 2.2 mg/kg bwt. The foal was intubated and anaesthesia maintained with sevoflorane inhalation agent. The foal was positioned in dorsal recumbency with the cranium in the centre of the CT gantry and a CT examination of the head and proximal neck carried out. A Siemens SOMATOM Volume Zoom M 4 slice helical
computed tomography scanner6 was used to acquire helical images collimated to an acquisition slice thickness of 2 mm from the articulation between the first and second cervical vertebra to the third most caudal cheek tooth. The total scan length was 26.8 cm and scan direction was caudo-cranial. The pitch was 1.75 with exposure at 120 V and 180 mA. The images were exported into a DICOM workstation and
manipulated using Osirix version 3.9.3 64 bit7. The data was reconstructed using both soft tissue and bone algorithms.
CT imaging findings The findings were interpreted by one author with experience of equine computed tomography. At the level of the second cervical vertebra there were multiple, coalescing hypoattenuating areas subcutaneously and dorsal to the right SS tendon with minimum Hounsfield units of –950, consistent with air (Fig 1). Caudally, the NL and the tendons of the left and right SS muscles were well defined. Within the body of the NL 4 cm caudal to the occipital bone were multiple hyperattenuating zones with maximum Hounsfield units of 700, consistent with avulsed bony fragments (Figs 2 and 3 and Supplementary Item 1). Cranial to this there was complete loss of the NL architecture. Present instead was amorphous soft tissue containing multiple coalescing zones of air, measuring –950 HU and hyperattenuating regions representing bony fragments.
Fig 2: Multiplanar reformatted sagittal CT image. Cranial is to the left. The recoiled nuchal ligament (white arrows) is well demarcated caudal to multiple hyperattenuating zones (red arrows) and coalescing hypoattenuating regions (green arrow).
The borders of the SS tendons were difficult to discern
3 cm caudal from the occipital bone to their insertion due to the presence of coalescing round hypoattenuating zones, again representing air and 1.5 cm of the left SS tendon remained at its insertion.
CT imaging diagnosis Computed tomographic diagnosis was complete avulsion of the NL from its insertion on the occipital bone and partial avulsions of the tendons of the right and left SS muscles. It was assumed due to the time between injury and imaging that the pockets of air were present due to the open skin wound rather than from infection.
Treatment and clinical course SS NL SS
The foal recovered well from anaesthesia. It was closely monitored and received ongoing treatment with flunixin, cefquinome, butorphanol and vitamin E. The skin wound was not closed, a dressing was applied and the area kept clean. Over the following 12 h the demeanour of the foal gradually improved. Butorphanol was withdrawn 36 h after admission. The head tilt and low head position did not change, but the foal generally coped well, ambulating freely and nursed from the mare without assistance. An ultrasonographic examination of the poll region was
carried out under standing sedation two days following injury. Images were acquired using a GE LOGIQ e portable ultrasound machine8. Linear array (5–13 MHz) and micro- convex (4–10 MHz) probes8 were used. The NL appeared normal to a point 5 cm caudal to the
Fig 1: Multiplanar reformatted transverse CT image at the level of the second cervical vertebra. Left is to the right of the image. The SS and NL are well defined. There is a pocket of air beneath the skin (red arrow). NL, nuchal ligament: SS, tendon of semispinalis capitis muscle.
poll after which its fibre pattern alignment was not appreciable. The tissue present in this region had a mixed echogenicity including multiple hyperechoic areas, some of which caused acoustic shadowing artefact thus hindering the examination of structures deep to them. These hyperechoic zones were likely a mixture of air and bony fragments. The tendons of the SS muscles were relatively normal to a
point 5 cm caudal from the occipital bone. Cranially from this was an anechoic area extending into the axial border of
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