J Toxicol Pathol 2012; 25: 179–182 Case Report Spontaneously Occurring Intracranial Lipomatous Hamartoma in a Young BALB/c Mouse and a Literature Review Tomo Sasaki1,2, Katsuhiko Yoshizawa1, Yuichi Kinoshita1,3, Hisanori Miki1, Ayako Kimura1, Takashi Yuri1, Norihisa Uehara1, and Airo Tsubura1 1 Department of Pathology II, Kansai Medical University, Moriguchi, Osaka 570-8506, Japan 2 Department of Toxicological Research, Research Laboratories, Maruho Co., Ltd., Kyoto, Kyoto 600-8815, Japan 3 Division of Cytopathology, Kansai Medical University Takii Hospital, Moriguchi, Osaka 570-8507, Japan Abstract: An intracranial lipomatous hamartoma was found in the third ventricle of a 7-week-old female BALB/cAnNCrlCrlj mouse. The nodule was composed of mature white adipose cells, which contained one large fat droplet, and there was no evidence of cytologi- cal atypia. The brain parenchyma at the retrosplenial granular cortex and the hippocampus in the cerebrum were slightly compressed, and the choroid plexus was dislocated downward. Scattered capillary vessels penetrated the nodule from the surrounding tissue. Based on these findings, the lesion was diagnosed as a lipomatous hamartoma that occurred from the roof of the third ventricle. This extreme- ly rare tumor-like nodule represents an overgrowth of the mature adipocyte population as a malformation rather than a true neoplasm. (DOI: 10.1293/tox.25.179; J Toxicol Pathol 2012; 25: 179–182) Key words : brain, cerebrum, lipoma, lipomatous hamartoma, mice, third ventricle Spontaneous primary tumors and tumor-like lesions used in an acute chemical toxicity study. The mice used in of the rodent central nervous system (CNS) are not well the study were housed in plastic cages with paper-chip bed- defined. In the mouse CNS, tumor-like lesions, such as li- ding (Paper Clean, SLC, Hamamatsu, Japan) in an air-con- pomatous hamartoma and epidermoid cysts, are rarely en- ditioned room at 22 ± 2°C and 60 ± 10% relative humidity countered1. Intracranial lipomatous hamartoma is a benign with a 12-h light/dark cycle and fed a commercial diet (CMF lesion characterized by the accumulation of mature adipose 30 Gy; Oriental Yeast, Chiba, Japan) and tap water ad libi- tissue within the ventricles or midline of the brain2,3. Intra- tum. All procedures were in accordance with the guidelines cranial lipomatous hamartoma never shows evidence of in- for animal experimentation at Kansai Medical University. vasion or any other indication of malignancy4. Therefore, it The mouse was anesthetized with isoflurane (Forane®; is considered to be a malformation and not a true neoplasm. Abbott Japan, Tokyo, Japan) and sacrificed by abdominal Although intracranial lipomatous hamartoma is thought to aortic transection. A complete necropsy was conducted. No be related to a neural tube closure defect during embryo- abnormalities were observed when the mouse was alive or genesis4 and may be associated with dysgenesis of the cor- during the necropsy. The brain and other organs were fixed pus callosum and lateral displacement of the adjacent blood overnight in 10% neutral buffered formalin. Coronal sec- vessels5, the histogenesis remains uncertain. In the present tions of the cerebrum and cerebellum were embedded in report, we describe the histopathological features of a lipo- paraffin, sectioned and stained with hematoxylin and eosin matous hamartoma in a young BALB/c mouse. (HE). Sequential sections were immunohistochemically The lipomatous hamartoma occurred in a 7-week-old stained for 1 h at room temperature with anti-proliferating female BALB/cAnNCrlCrlj mouse that was purchased from cell nuclear antigen (PCNA) antibody (monoclonal, clone Charles River Laboratories Japan, Inc. (Atsugi, Japan) and PC10, 1:100 dilution; Leica Biosystems, Newcastle upon Tyne, UK), anti-glial fibrillary acidic protein (GFAP) anti- bodies (polyclonal, 1:500 dilution; Dako, Carpinteria, CA, Received: 12 December 2011, Accepted: 28 February 2012 Mailing address: Katsuhiko Yoshizawa, Department of Pathology USA) or anti-alpha-smooth muscle actin (α-SMA) antibody II, Kansai Medical University, 10-15 Fumizono, Moriguchi, Osaka (monoclonal, clone 1A4, 1:500 dilution; Dako). Antigen re- 570-8506, Japan trieval was necessary for PCNA and GFAP visualization and TEL: 81-6-6993-9432 FAX: 81-6-6992-5023 was conducted by pressure-cooker heating (Pascal, Dako). E-mail: [email protected] The antigen-antibody complexes were identified using a ©2012 The Japanese Society of Toxicologic Pathology streptavidin-biotin (LSAB) staining kit (Dako) according to This is an open-access article distributed under the terms of the Cre- the manufacturer’s instructions. The reaction products were ative Commons Attribution Non-Commercial No Derivatives (by-nc- nd) License <http://creativecommons.org/licenses/by-nc-nd/3.0/>. visualized with 3-3’-diaminobenzidine tetrahydrochloride. 180 Intracranial Lipomatous Hamartoma in a BALB/c Mouse (Fig. 2f). A detailed pathological examination of the organs and tissues revealed no additional lesions in the brain and no distant metastases (data not shown). None of the other study animals had brain abnormalities; therefore, this lesion was believed to be spontaneously occurring and unrelated to chemical exposure. The lesion was a well-demarcated nodule located in the ventricle and composed of multiple clusters of mature white adipose cells, which are characteristics of a benign lipomatous lesion. The cells had a low level of proliferative activity, as no PCNA signals were seen in the nodule. The characteristics of the lipomatous lesion were not suggestive of a choristoma, which is an overgrowth of heterotopic nor- mal mature resting adipocytes. Rather, the lesion contained Fig. 1. Lipomatous hamartoma in the third ventricle of the cere- an overgrowth of the mature adipocyte population that brum. HE stain, bar = 1 mm. normally occurs at the site of origin; therefore, it was diag- nosed as a lipomatous hamartoma that developed from the roof of the third ventricle. This lipomatous lesion appears Histopathological findings were reviewed by a toxicologic to have occurred in the interstitium of the choroid plexus pathologist certified by the Japanese Society of Toxicologic of the third ventricle, and the choroid plexus was displaced Pathology and the International Academy of Toxicologic downward by the adipose tissues. Capillary vessels in the Pathology (K.Y.), according to the previously defined histo- nodule appeared to be nutrient vessels from the surround- pathological terminology and diagnostic criteria3,5. ing tissue; hence, our case should be distinguished from an Histopathologically, a well-demarcated nodule was angiolipoma, which includes numerous small vessels. Other observed in the third ventricle (Fig. 1). It was composed elements, such as neural tissues, bone and cartilage, were of well-differentiated adipocytes resembling those seen not present4,6,7. in adipose tissue, and each adipocyte contained one large The terms “lipoma,” “lipomatous hamartoma” and fat droplet (Fig. 2a). Cytological atypia was not observed. “choristoma” have been used for lesions similar to our case, PCNA signals were not seen in any nuclei of the cells in the and these lesions have been reported in several kinds of nodule (Fig. 2b), suggesting a low level of proliferation. The laboratory animals and humans. Lipomas of the CNS have brain parenchyma at the retrosplenial granular cortex and been observed in the pig, horse, cow, dog, rabbit and fox8. the hippocampus in the cerebrum were slightly compressed; In humans, lipomas or lipomatous hamartomas are also rare however, no degenerative changes were seen in the adjacent disorders in the CNS6,9,10. The recent World Health Organi- tissues (Fig. 2c). GFAP-positive glial cells did not proliferate zation (WHO) classification of tumors of the CNS11 still con- within the nodule or the surrounding parenchyma (Fig. 2d). tains the term “lipoma” for humans. Lipomas are classified Scattered capillary vessels penetrated the nodule from the as mesenchymal, non-meningothelial tumors and described surrounding tissue (Fig. 2e) and were visualized by α-SMA as “benign lesions that microscopically resemble normal immunohistochemistry (data not shown). The choroid plex- adipose tissue.” Additionally, lipomatous hamartomas is us, which is usually located in the roof of the third ventricle, used as a synonym of lipomas in the AFIP Atlas of Tumor was displaced downward due to compression by the nodule Pathology12, and it is noted that a malformative mass com- Table 1. Literature Review: Intracranial Lipomatous Lesions in Rodents Occurrence / Species Report type Diagnosis Frequency Reference total number of animals Mouse NCTR* database Lipoma 15/45,983 (BALB/c) 0.033% (BALB/c) Morgan KT et al., 1984 0/31,427 (other strains) AFRC and MRC Neuropatho- Lipoma 110/75,070 (some strains 0.15% (some strains Fraser H et al., 1986 genesis Unit database including BALB/c) including BALB/c) The Jackson Laboratory Lipomatous hamartoma 52 (0 in BALB/c)/nearly 0.52% Adkison DL et al., 1991 database 10,000 NTP** historical data Lipoma 1/4,894 (B6C3F1) 0.02% (B6C3F1) Haseman JK et al., 1999 Rat NTP** historical data Lipoma / Lipomatous 0/7,786 (F344) 0% (F344) Haseman JK et al., 1990 hamartoma Case report (first report in rat) Intracranial lipoma 1/Unclear (Wistar) - Brander P et al., 1995 *NCTR: National Center for Toxicological Research. **NTP: National Toxicology Program. Sasaki, Yoshizawa, Kinoshita et al. 181 Fig. 2. Histopathological and immunohistochemical findings of a lipomatous hamartoma. (a) The mass is composed of well-differentiated adipocytes, which contain a single large fat droplet, without atypia. HE stain, bar = 25 μm. (b) PCNA signals are not seen in any nuclei of the adipocytes in the nodule. Bar = 25 μm. (c) Brain parenchyma of the retrosplenial granular cortex and the hippocampus in the cerebrum were slightly compressed (arrow). HE stain, bar = 200 μm. (d) GFAP-positive glial cells did not proliferate in the nodule and surrounding brain parenchyma. Bar = 200 μm. (e) Scattered capillary vessels penetrated the nodule from the surrounding tissue (arrowhead). HE stain, bar = 100 μm. (f) The choroid plexus was displaced downward due to compression by the nodule. HE stain, bar = 100 μm. posed of mature adipose tissue is more appropriately called expect a neural tube closure defect during embryogenesis4. a “lipomatous hamartoma.” According to the diagnostic cri- Their histogenesis remains uncertain; however, the term “li- teria from goRENI3, a lipomatous lesion in the cerebrum is pomatous hamartoma” may be more appropriate6,9. defined as a lipomatous hamartoma in rodents. Intracranial Previous reports of lipomatous lesions in the rodent lipomatous lesions are frequently localized in the medial CNS are summarized in Table 1. According to the National line and especially the corpus callosum, where one could Center for Toxicological Research database4, lipomas were 182 Intracranial Lipomatous Hamartoma in a BALB/c Mouse found in 15 of 45,983 (0.033%) BALB/c mice and 0 of 31,427 tumors found in several strains of mice. J Natl Cancer Inst. mice from other strains. Fraser et al. identified lipomas in 72: 151–160. 1984. [Medline] 5. Morgan KT, and Sheldon WG. Lipoma, brain, mouse. In: 110 of 75,070 (0.15%) mice including BALB/c mice13. The Monographs on Pathology of Laboratory Animals, Nervous characteristics of the present case were similar to those of the System. TC Jones, U Mohr, and RD Hunt (eds). Springer- above cases. In contrast, The Jackson Laboratory2 evaluated Verlag, Heidelberg. 130–134. 1988. nearly 10,000 mice, and lipomatous hamartomas were found 6. Lindboe CF. Leptomeningeal lipomatous hamartoma over- in none of the BALB/c mice but were found in 52 (0.52%) lying a midline cleft of the ventral pons. Clin Neuropathol. mice of other strains. Regarding B6C3F1 mice, only 1 of 16: 309–311. 1997. [Medline] 4,894 (0.02%) mice had a lipomatous hamartoma according 7. Turnquist SE, and Miller RB. Intracranial ossifying lipoma to the National Toxicology Program (NTP) historical data14. in a juvenile pig. Vet Pathol. 30: 580–582. 1993. [Medline] These data indicate that intracranial lipomatous lesions in [CrossRef] mice are extremely rare. In rats, there are only two reports of 8. Luginbühl H, Frankhauser R, and McGrath JT. Sponta- intracranial lipomas, one case in a Wistar rat15 and none in neous neoplasms of the nervous system in animals. Progr Neurol Surg. 2: 134–135. 1968. F344 rats (NTP historical data16). This suggests that the oc- 9. Budka H. Intracranial lipomatous hamartomas (intracra- currence of lipomatous lesions in rats is lower than in mice. nial “lipomas”). A study of 13 cases including combina- To the best of our knowledge, BALB/c mice are not tions with medulloblastoma, colloid and epidermoid cysts, commonly used in toxicity and pharmacological studies, angiomatosis and other malformations. Acta Neuropathol. and historical control data for BALB/c brain lesions have 28: 205–222. 1974. [Medline] [CrossRef] not been well reported. Our case provides valuable infor- 10. Zámecník J, and Kyncl M. Lipomatous hamartoma of the mation on the histopathology of an intracranial lipomatous brain—malformations of the subarachnoid space. Cesk Pa- hamartoma in a BALB/c mouse. tol. 37: 163–167, 2001 (article in Czech and abstract in Eng- lish). [Medline] Acknowledgments: The authors thank Ms. T. Akamatsu for 11. International Agency for Research on Cancer (IARC). her technical assistance and Ms. A. Shudo for manuscript WHO Classification of Tumors of the Central Nervous Sys- tem, 4th ed. DN Louis, H Ohgaki, OD Wiestler, and WK preparation. The authors declare that they have no compet- Cacenee (eds). WHO Press, Geneva. 2007. ing financial interests. This research was supported in part 12. Peter CB, and Brend WS. Tumors of the Central Nervous by a Grant-in Aid for Scientific Research (C) from the Japan System. AFIP Atlas of Tumor Pathology, 4th series, fascicle Society for the Promotion of Science (22591954). 7. American Registry of Pathology, Washington DC. 2007. 13. Fraser H. 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