Case Report Magnetic resonance imaging of a cholesterol granuloma and hydrocephalus in a horse B. E. B. MAULET*, M. BESTBIER † , E. JOSE-CUNILLERAS † , J. A. SCRINE ‡ AND R. MURRAY † Drève des pinsons 16, B-7850 Enghien, Belgium; † Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU; and ‡ Equine Veterinary Practice, Bognor Road, Horsham, West Sussex RH12 3SH, UK. Keywords: horse; magnetic resonance imaging; cholesterol granuloma; hydrocephalus 74 EQUINE VETERINARY EDUCATION Equine vet. Educ. (2008) 20 (2) 74-79 doi: 10.2746/095777308X273787 Summary Magnetic resonance imaging (MRI) was used to diagnose cholesterol granulomas in the choroid plexuses in the lateral ventricles of a horse. This report provides, in addition to the clinical signs and pathology findings, a precise description of the MRI appearance of a cholesterol granuloma. Case history A 17-year-old hunter-type mare presented with a history of intermittent episodes of malaise with depression of 8 months’ duration. Several short episodes of depression had been noted by the owner over a longer period but resolved without treatment. During the first episode of malaise that required veterinary intervention, the mare was depressed, pyrexic (40.5°C), tended to stay with the head in a corner (not actually head pressing) and showed one episode of circling to the right. A blood sample taken at the time showed: red blood cells 6.43 x 10 12 /l (reference range [rr] 5.42–9.62 x 10 12 /l ), PCV 27% (rr 29.2–46.4%), haemoglobin 96 g/l (rr 95–163 g/l), mean corpuscular volume 51 fl (rr 44–56 fl), mean corpuscular haemoglobin concentration 306 g/l (rr 308–372 g/l), white blood cells 7.3 x 10 9 /l (rr 4.8–10.8 x 10 9 /l), platelets 161 x 10 9 /l (rr 113–299 x 10 9 /l). The mare was treated with dexamethasone (Duphacort Q, 400 mg i.v.) 1 , oxytetracycline (Engemycin 10%, 2800 mg i.v.) 2 and flunixin meglumine (Meflosyl 5%, 600 mg i.v.) 1 . Major improvement occurred within 2 weeks. During the following 6 months, the mare had one brief episode of depression that improved without treatment within 24 h, but was otherwise normal. After those 6 months (2 months prior to referral), she suffered an episode of colic signs, mild pyrexia and lethargy followed immediately by an episode of syncope with unconsciousness of one hour’s duration. On regaining her feet, she had several episodes of ‘petit mal’ seizures (trance-like state), reduced mentation and a tendency to hold her head to the right. Right panniculus reflexes were reduced and right side weakness was apparent during the tail-pull test and hopping tests. No significant abnormalities were detected using extensive diagnostic testing; abdominocentesis, rectal palpation, abdominal ultrasound, gastroscopy, chest and head radiography. Haematology and biochemistry identified no abnormalities other than mildly elevated inflammatory proteins: serum globulin 41 g/l (rr 26–36 g/l) and fibrinogen 4.0 g/l (rr 0.9–3.7g/l). An ELISA test for antibodies to Borrelia burgdorferi was negative. Although lumbosacral cerebrospinal fluid analysis was blood contaminated, analysis demonstrated increased numbers of segmented mature nondegenerate neutrophils once allowance had been made for the blood contamination (red blood cells 0.05 x 10 9 /l, total number of nucleated cell count 0.2 x 10 9 /l, protein 4.9 g/l, creatine kinase 645 iu/l, glucose 3.9 nmol/l, total number of cells 0.17 x 10 12 /l). A 4 week course of treatment with doxycycline (Doxycycline) 3 10 mg/kg bwt q. 12 h per os was instigated. The mare had repeated episodes of depression, approximately every 2–3 days, with lack of awareness of her environment, decreased appetite and sometimes appeared centrally visually impaired with reluctance to lift the right limbs. No abnormal signs had been noted between these bouts. Because the mare did not improve, she was referred to the Animal Health Trust for magnetic resonance imaging (MRI) of the brain and atlanto-occipital cerebrospinal fluid (CSF) centesis under general anaesthesia. Clinical examination On the day of presentation at Animal Health Trust, the mare was in good bodily condition but not overweight. She was mildly lethargic and depressed. A thorough neurological examination was performed and revealed a slightly decreased menace response on the right side. When the sway test was performed at the walk on the right, the mare could be pulled off-stride *Author to whom correspondence should be addressed.