A Light and Electron Microscopic Study

Abstract. A tumor mass removed from the subcutaneous tissue of the shoulder of a dog had the light and electron microscopic features of extraneuraxial meningioma. The neoplasm probably arose from arachnoid cap cells displaced during embryogenesis. Although intracranial canine meningiomas are common [ 141 no primary menin-gioma, to our knowledge, has been reported outside the central nervous system in dogs or other animal species. Extraneuraxial meningiomas occur occasionally in man and are predominantly in the head and neck area [13]. We are aware of only one such neoplasm in man in which the meningiomatous nature of the lesion was confirmed by electron microscopy [13]. There is no similar ultrastructural study in the veterinary literature. Case History A 2 x 3 x 4-centimeter mass was removed from the subcutaneous tissue of the shoulder of a 7l/z-year-old German Shepherd crossbred male dog. The tumor had been enlarging for several months. Six months after surgery there was neither local recurrence nor metastases. Materials and Methods The tumor was fixed in 4 % neutral buffered formalin. Representative samples were embedded in paraffin and 5-micrometer-thick sections were stained with hematoxylin and eosin (HE), periodic acid-Schiff (PAS), Masson’s trichrome and Gomori’s reticulin for light microscopy. Several 1-millimeter cubes from various areas of the tumor were taken for electron microscopy, fixed in buffered formalin (4%, pH 7. 3, then in 2 % osmium tetroxide, dehydrated in graded alcohols and propylene oxide and embedded in epon 812. Semi-thin sections were stained with toluidine blue. Diamond-cut thin sections were stained with uranyl acetate and lead citrate