Malignant pinealoma observed in the deep cerebral parenchyma of a male Wistar rat

Abstract

This report describes a case of spontaneous malignant pinealoma in a 90-week-old male Wistar rat. The tumor mass occurred in the deep cerebral parenchyma and no intact pineal gland was observed in the area between the posterior-dorsal median line of the cerebrum and the cerebellum. The tumor was characterized by a large nodular proliferation occupying the central area of the brain, extending from the dorsal surface to the base of the brain, corresponding to the thalamus. The tumor cells had round to irregular oblong nuclei approximately 5-17 μm in diameter and showed faintly or moderately eosinophilic cytoplasm and indistinct cell boundaries. Immunohistochemically, the tumor cells were positive for synaptophysin and partially positive for neuron-specific enolase (NSE). The tumor showed malignant features including cellular pleomorphism, high mitotic index, necrotic foci, and invasive and extensive growth and was, therefore, diagnosed as an extremely rare malignant pinealoma in the deep cerebral parenchyma.

Keywords: Wistar; pineal gland; pinealoma; rat; synaptophysin.

Fig. 1.

Macroscopic features of the tumor in the transversal cut surface of the formalin-fixed brain passing through the location where the pineal gland is normally present. A yellowish-brown mass occupies the central area of the brain, extending from the dorsal surface to the base of the brain corresponding to the thalamus-pons, and expands from the cerebral median line to both sides of the brain stem. The arrow indicates the border between the tumor and brain parenchyma.

Fig. 2.

(A) Schematic view of the tumor (filled with orange color) in a longitudinal median plane of the brain. The areas filled with black color indicate the dilated ventricles. The blue bar (a–f) indicates the anatomical location where the specimen was prepared. (B) Low-magnification images of each histological specimen stained with hematoxylin and eosin (HE) (a–f). The tumor mass extends from the region where the pineal gland is normally present to the thalamus (d) and pons (e). The mass is invading the third and lateral ventricles and reaches the fourth ventricle (b–f). The third and lateral ventricles in the anterior area of the tumor are moderately dilated (a, b).

Fig. 3.

(A) Tumor cells arranged in sheets and partially compartmentalized by fibrous connective tissues into incomplete lobules or nests. Hematoxylin and eosin (HE). Bar=100 µm. (B) Tumor cells of varying size and shape, with round, oval, or irregular oblong nuclei and faintly eosinophilic cytoplasm with indistinct boundaries. The smaller nuclei of the tumor cells contain richer chromatin. Mitotic figures (arrows) are frequent. HE. Bar=50 µm. (C) Large necrotic areas with coagulation necrosis are present within the tumor. The necrotic tumor cells show karyopyknosis. HE. Bar=200 µm. The inset shows a higher-power view of the necrotic tumor cells with karyopyknosis. Bar=50 µm. (D) At the margins of the tumor mass, tumor cells invade the brain parenchyma and form island-like nests. HE. Bar=200 µm. (E) Pseudo-rosette formation around the blood vessels (arrows) and cyst-like structures containing eosinophilic liquid material (arrowheads). HE. Bar=100 µm. The inset shows a higher-power view of the pseudo-rosette. Bar=50 µm. (F) Tumor cells incompletely compartmentalized into various sizes of nests accompanied by blood vessels by argentaffin fibers. Silver impregnation. Bar=100 µm.

Fig. 4.

(A) The cytoplasm of most tumor cells is positive for synaptophysin. Immunohistochemistry for synaptophysin. Bar=50 µm. (B) The tumor cells are partially positive for neuron-specific enolase (NSE). Positive staining is visible in a small focus comprising tumor cells with relatively large nuclei. Immunohistochemistry for NSE. Bar=50 µm.