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Large, extremely intricate labyrinthine structures were observed during an electron microscopic examination of a secretory meningioma that originated in the sphenoid ridge of a 73-year-old man. In many neoplastic cells, these labyrinthine structures formed round-shaped regions within the cytoplasm, and profiles indicated their internal structure consisted of numerous thin fragments of cytoplasm and intervening flocculent material. These labyrinthine structures did not exhibit apparent topographic association with pseudopsammoma bodies, and direct communication with the extracellular space by very thin channels was rarely observed. The structures resembled the “intracytoplasmic lumina” commonly seen in epithelial neoplasms; but they did not appear to be true “intracytoplasmic” closed structures but rather deep and elaborate invaginations of the plasma membrane into the cytoplasm. These structures are distinct from pseudopsammoma bodies and might represent another expression of the epithelial properties of neoplastic cells in this subtype of meningioma. Although their pathogenesis or significance remain unknown, these structures may significantly increase the surface area of neoplastic cells and facilitate the uptake of extracellular material.

An isolated proliferation of pericytes is a unique vascular reaction seen almost exclusively in the stroma of secretory meningioma. We report the results of immunohistochemical and ultrastructural studies of a pericytic proliferation that was found in two cases of meningioma (a secretory meningioma of the sphenoid ridge and a parasagittal atypical meningioma showing predominantly fibroblastic features). Pericytes had hyperchromatic nuclei and scant cytoplasm, and showed stratification or formed small clusters within the walls of small blood vessels. They occasionally showed close contact with pseudopsammoma bodies in secretory meningioma. Pericytes showed immunoreactivity for α-smooth muscle actin but were not immunoreactive for desmin. They also exhibited characteristic ultrastructural features of pericytes, including the presence of microfilaments and abundant pinocytotic vesicles, and investment by the basal lamina. This isolated pericytic proliferation is likely a peculiar response of the vascular wall, probably induced by some cytokines secreted from neoplastic meningothelial cells. The close contact of proliferating pericytes with pseudopsammoma bodies suggests a close pathogenetic association between them. The occurrence of pericytic proliferation that was found in our second case (atypical meningioma with predominantly fibroblastic features) is exceptional and has not been documented to date.

We report the autopsy findings of a case of disseminated mucormycosis caused by Cunninghamella bertholletiae, a rare pathogenic fungus of the family Mucoraceae. The patient was a 49-year-old woman with B-lymphoblastic leukemia with hyperdiploidy, who died of progressive heart failure 4 months after induction chemotherapy successfully brought about complete remission of the leukemia. Granulocyte colony-stimulating factor (G-CSF) had been administered along with anti-neoplastic drugs, and her blood neutrophil count was markedly elevated. Autopsy revealed disseminated mycotic thromboembolism and abscess formation in the heart, lung, liver, kidney, and spleen. The most marked feature was a large mural thrombus in the left ventricle containing numerous fungal hyphae. In the myocardium and disseminated foci in visceral organs, giant cell-rich, fibrotic reactions to the mycotic infection were observed. Both the formation of a large intra-ventricular mural thrombus and giant cell reactions are rare findings in mucormycosis. We considered that the recovery and marked increase in neutrophil count induced by chemotherapy and G-CSF administration prolonged the clinical course and pathologically elicited an atypical, giant cell reaction to the mycotic infection. The prolonged clinical course also contributed to the formation of an unusually large intra-ventricular mural thrombus.

We report a case of segmental arterial mediolysis (SAM) that involved the middle colic artery, and present some pathologic alterations found in mesenteric small arteries and veins. The patient, a 52-year-old woman, underwent an emergency laparotomy for acute intra-abdominal hemorrhage, and a segment of the transverse colon with hemorrhagic mesocolon was excised. Microscopic examination demonstrated two separate lesions of SAM in the middle colic artery. The involved arterial segments showed a partial to circumferential loss of the media (mediolysis) and intima associated with the formation of a pseudoaneurysm. Smooth muscle cells adjacent to the mediolysis showed various degenerative changes. In addition, we found multiple, tiny foci of degenerative lesions affecting the outer media in the wall of small arteries. Subendothelial vacuoles and nodular intimal proliferation were also noted in small veins. Whereas SAM chiefly affects large or medium-sized arteries, small blood vessels, including veins, are also affected. The present case is unusual in that degeneration of medial smooth muscle cells was clearly observed in the arterial walls, and the small veins were affected by lesions similar to those in arteries. We suspect that a phenotypic modulation of vascular smooth muscle cells induced by some genetic vulnerability plays a role in the pathogenesis of SAM.

A 74-year-old man presented with symptoms suggestive of acute pancreatitis, and a mass lesion measuring 25 mm was detected in the pancreatic head. Cytological and histopathological examinations of EUS-FNA specimens taken from the lesion demonstrated small cell (neuroendocrine) carcinoma. Tumor cells were immunoreactive for cytokeratin, synaptophysin, chromogranin A, CD56, and TTF-1, and PET-CT of the chest revealed a small tumor in the upper lobe of the left lung. Pulmonary carcinoma, particularly small cell carcinoma, infrequently presents with a solitary metastatic lesion in the pancreas as an initial manifestation and clinically simulates a primary pancreatic neoplasm. Because primary small cell carcinoma of the pancreas is very uncommon, metastasis from the lung should always be considered when evaluating pancreatic neoplasms showing a “small cell” morphology. Immunohistochemistry for TTF-1 is useful for determining the pulmonary origin of this type of neoplasm, and its application to cytology specimens is recommended.