Neuropathological evaluation showed a tumor of low to moderate cellularity composed of different cell populations (Fig. 3A). Dysplastic large ganglion cells with one or two large round nuclei, a large basophilic nucleolus and a bright reticular karyoplasm were conspicuous. The cytoplasm was granular, resembling Nissl-substance. These cells were either scattered throughout the tumor or formed small clusters within a microcystic matrix (Fig. 3E).
The second component was of epithelial derivation. Strongly cytokeratin-positive cells formed small clusters and tubuli (Fig. 3B) with a lobulating reticulin-fiber network. On the basis of their nuclear and cytoplasmic morphology they resembled adenohypophyseal cells, which was corroborated by positive immunoreactivity for GH (Fig. 3C), FSH, prolactin (Fig. 3D) and chromogranin-A. Some cells were also GFAP-positive. Another epithelial component was arranged irregularly with only scarce reticulin-fibers (Fig. 3F). These cells were exclusively GH-positive (Fig. 3G), but did not express other beta-chains of pituitary hormones. Some nuclei were slightly pleomorphic. These areas were adenoma-like, however, lacked the homogeneous cellular picture typical for adenoma. Several small cysts containing PAS-positive material were lined by a flat or cuboidal epithelium. According to the location of the lesion they were interpreted as Rathke´s cysts of the pars intermedia (Fig. 3A). An additional cytokeratin-positive population consisted of diffusely distributed small cells with round nuclei and only scarce cytoplasm. These cells exhibited a peculiar intermediate immunostaining pattern with cytoplasmic globular inclusions positive for cytokeratin (Fig. 3H) and chromogranin-A, neurofilament-positive filamentous material and synaptophysin-positive cell membranes.
Surrounding the mixed neuronal-adenohypophyseal areas a spindle-cell component was present forming a dense matrix of fibres oriented in parallel, in part exhibiting a storiform pattern (Fig. 4A). These cells showed a faint eosinophilic cytoplasm and were embedded within a delicate reticulin-fibre network (Fig. 4B). Nuclei were elongated with tapered as well as blunt ends. The karyoplasm was inconspicuous with membrane-bound heterochromatin and a small eosinophilic nucleolus. These cells were strongly immunoreactive for S-100 protein (Fig. 4C) and to a lesser degree also for vimentin and GFAP. The histomorphological characteristics and the pattern of immunoreactivity were reminiscent of an Antoni A-schwannoma. However, there was also immunostaining for neurofilament (Fig. 4D) and for synaptophysin. Histological sections stained for reticulin-fibers (5A), cytokeratins (5B), protein S100 (5C), beta-HCG (5D), neurofilament (5E), and vimentin (5F). Herring-bodies were not present. All components of the lesion did not exhibit any mitotic figures and the labeling index for MIB-1 was below 2%.