Meningeal cholesterol granulomas in two meerkats (Suricata suricatta)

CHOLESTEROL granulomas form as a result of an inflammatory foreign body response to the accumulation of cholesterol crystals within tissues (Leon and others 2002). In human beings, cholesterol granulomas are an important intracranial lesion, and occur most commonly in association with chronic middle ear disease. Although they are reported in the choroid plexus of the lateral and fourth ventricles in up to 20 per cent of horses at postmortem examination (Jackson and others 1994), cholesterol granulomas are rare findings in other animals. In dogs, they have been reported in the middle ear, maxillary sinus and fourth ventricle and cerebellopontine angle of the brain (Mould 1990, O’Brien and others 1990, Cox and Payne-Johnson 1995). A cholesterol granuloma has been described in association with meningioma in a cat (Schulman 2005). Cholesterol granulomas have also been reported in the intracranial meninges of two meerkats (Suricata suricatta; family Herpestidae) at separate zoos in the USA (Schulman 1997, Sladsky and others 2000). This short communication describes two cases of meningeal cholesterol granuloma in meerkats from collections in the UK. Two meerkats were submitted for postmortem examination to the Royal Veterinary College within a period of 17 months. Case 1, a male meerkat aged three years and five months, was submitted in May 2003 from a private collection in Hertfordshire. The animal was described as off-colour before its death but no blood samples had been taken. Case 2 was submitted in October 2004 from a small zoo in Wales. This adult male meerkat had initially presented two months before its death with marked ataxia, which slowly improved but did not resolve. This animal’s serum cholesterol level had been 11·9 mmol/l in March 2003. An intracranial cholesterolbased mass was suspected, and steps were taken to reduce the level of cholesterol in the animal’s diet. Despite this, the animal developed left-sided weakness 10 days before death, which progressed to hemiplegia; it was humanely euthanased. In both cases, there was a large (3·5 x 1·5 x 1·0 to 1·5 cm and 3·0 x 3·5 x 1 to 1·5 cm), adherent, brown, granular meningeal mass occupying most of the dorsal surfaces of the cerebral hemispheres (Fig 1). Examination of cytological smears confirmed the presence of cholesterol crystals. Brain sections showed compression of the cerebral parenchyma, and in case 2 the ventricular spaces of the brain were dilated. Representative specimens from the brains and other tissues were fixed in 10 per cent neutral-buffered formalin, processed by routine methods for histology and embedded in paraffin wax. Glass slide-mounted sections (5 μm) were stained with haematoxylin and eosin, and further slides were stained for iron using Perl’s Prussian blue. Formalin-fixed specimens of the meningeal mass from case 2 were snap-frozen, cryosectioned and stained with Schultz stain for cholesterol. In both animals the cerebral leptomeninges were markedly expanded by a large, irregularly shaped mass composed of densely packed clusters of cholesterol clefts surrounded by foreign body-type multinucleate histiocytic giant cells and foamy macrophages (Fig 2); many of the macrophages contained haemosiderin, revealed in sections stained with Perl’s Prussian blue. The Schultz reaction for cholesterol was positive in case 2. There was marked cerebral compression and distortion, with multifocal invasion of the Virchow-Robin spaces. Multifocal haemorrhage was noted inside the granulomas, and within the superficial cerebral cortex in case 2. A section of the calvarium from case 2 showed marked invasion and disruption of bone, with mild reactive bone formation. In case 1, smaller, similar masses expanded the pericardium. Other postmortem findings in this animal included intestinal salmonellosis, hepatic lipidosis, mineralisation of the bronchiolar walls and lymphoid hyperplasia of the mandibular lymph node. In case 2, glomerulonephritis, glossitis, gastritis, hepatic lipidosis and lymphocytic thyroiditis were also noted. Based on the gross and histopathological findings, meningeal cholesterol granuloma was diagnosed in both animals. In human beings, one person out of every two to three million is affected by intracranial cholesterol granulomas per year (Francis and others 2005). Cholesterol granulomas have been found in the intracranial dura in human patients, but the incidence in the meninges of any species is not known as they have rarely been reported (Leon and others 2002). The typical histological appearance of densely packed cholesterol clefts with an associated granulomatous inflammatory reaction is diagnostic (Leon and others 2002). Ventricular dilation (as seen in case 2) and hydrocephalus may result from increased intracranial pressure and obstructed flow of cerebrospinal fluid as the mass develops within the skull (Johnson and others 1993). Adjacent bone erosion was noted in case 2 and in one meerkat in a previous report (Sladsky and others 2000), and is often seen in human beings suffering from cholesterol granulomas in the sinus cavities (Leon and others 2002). In the USA, meningeal cholesterol granulomas have been reported in a meerkat from the North Carolina Zoological Park (NCZP) and a second animal in a Californian collection, from which tissues were submitted to the Armed Forces Institute of Pathology (Schulman 1997, Sladsky and others 2000). In the UK there was an unreported case in an adult male meerkat at Cotswold Wildlife Park in 2004 (P. Kettlewell, personal communication). Neurological signs were noted in all the previous cases of meningeal cholesterol granuloma in meerkats but not in case 1 in the present report, which may have been due to poor observation. Other tissues reported to Veterinary Record (2006) 158, 636-637