SPONTANEOUSLY-ARISING DISEASE Ependymal Cyst in the Cerebrum of an African Green Monkey (Chlorocebus aethiops) K.-S. Chang * , S.-R. Lee † , S.-W. Kim † , Z.-H. Cho ‡ , H.-Y. Son x , D. Kim * and K.-T. Chang † *College of Veterinary Medicine, Kangwon National University, Chuncheon, Kangwon 200-701, † National Primate Research Center (NPRC), Korea Research Institute of Bioscience and Biotechnology (KRIBB), Cheongwon, Chungbuk 363-883, ‡ Neuroscience Research Institute (NRI), Gachon Medical and Science School, Incheon 405-760 and x Department of Veterinary Pathology, College of Veterinary Medicine, Chungnam National University, Daejeon 305-764, South Korea Summary A focal lesion was detected by magnetic resonance imaging in the right caudal occipital lobe of the cerebrum in an African green monkey (Chlorocebus aethiops). Neurological signs were not observed in this animal. At necropsy examination, an 8 mm wedge-shaped intracranial cavity was found, which apparently did not communicate with the ventricles. Microscopically, the inner surface of the cavity was lined by ciliated cuboidal epithelium with positive immunoreactivity for S100 protein, glial fibrillary acidic protein and cytokeratin. Based on the gross, microscopical and immunohistochemical findings the lesion was classified as an ependymal cyst. To the best of our knowledge, this is the first report of an ependymal cyst in an African green monkey. Ó 2011 Elsevier Ltd. All rights reserved. Keywords: African green monkey; cerebrum; ependymal cyst Ependymal cysts are benign, non-infectious and non- inflammatory lesions of the central nervous system that are believed to originate from aberrant migration of ependymal cells during development (Moriyama et al., 2007). Despite being benign, ependymal cysts can be associated with neurological signs if they enlarge or press into critical neural structures. Epen- dymal cysts are lined by cells with features consistent with the cells lining the ventricles (Hirano and Hirano, 2004; Bergin et al., 2008). Most human ependymal cysts have been reported in the cranial cavity and less commonly within the spinal cord. Most of the cysts within the cranial cavity do not communicate with the ventricles (Takci et al., 2006). Ependymal cysts have been reported in non-human primates, rats and dogs (Gotow and Hashimoto, 1980; Bergin et al., 2008; Wyss-Fluehmann et al., 2008). A 17-year-old, female African green monkey (Chlorocebus aethiops) of 3.25 kg body weight under- went magnetic resonance imaging (MRI) to obtain baseline measurements for screening of neurodegener- ative diseases in aged monkeys. A cyst-like structure was found in the right caudal cerebral hemisphere (Fig. 1). The lesion approached the posterior horn of the lateral ventricle; however, a connection with the ventricle was not detected. The lateral ventricles appeared symmetrical. This animal was unsuitable for neural imaging studies and was subsequently humanely destroyed and submitted for necropsy examination. The occipital lobe of the right cerebral hemi- sphere contained a triangular to wedge-shaped fluid-filled cavity. The cavity was confined entirely to the white matter and measured approximately 0.8 cm in diameter at its widest aspect. No other sig- nificant gross lesions were observed and the cavity did not communicate cranially with the ventricular system (Fig. 2). The brain and samples of major organs were fixed in 10% neutral buffered formalin. Tissues were pro- cessed routinely, embedded in paraffin wax and Correspondence to: K.-T. Chang (e-mail: changkt@kribb.re.kr). 0021-9975/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcpa.2011.01.005 J. Comp. Path. 2011, Vol. 145, 235e239 Available online at www.sciencedirect.com www.elsevier.com/locate/jcpa