Arthritis and ankylosis in twy mice with hereditary multiple osteochondral lesions: with special reference to calcium deposition.

A murine autosomal recessive mutant named twy (tiptoe walking-Yoshimura) mouse showing multiple osteochondral lesions including ankylosis of the vertebral column and limb joints underwent sequential histopathological analysis of posterior limb joint lesions and intervertebral disc lesions. In the articular cartilage, a decrease in alcian blue-positive extracellular matrix and the presence of degenerated collagen fibers were found at the age of around 4-8 weeks. Calcium deposits in the articular cartilage were found at that time and later in the articular space and synovial tissue. Calcium deposits were also found in the intervertebral discs at 4 weeks. Using electron microscopy, some of the crystals were seen inside small vesicles. In both joints, degeneration of, and calcium deposition in, the articular cartilage progressed with age, finally producing bony ankylosis. These histological observations suggest that calcification and degeneration of the articular cartilage are the major factors in the pathogenesis of joint disorders in the twy mouse, and this mutant mouse provides a good model for studying the process and mechanism of osteoarthritic lesions, destructive arthritis and ankylosis.

Inflammatory pseudotumor of the stomach: report of a highly infiltrative case with electron microscopic and immunohistochemical studies.

A large, poorly demarcated, elevated lesion over the area ranging from the lower end of the esophagus to the lesser curvature of the cardiac region was examined in a 19 year old woman, and demonstrated an irregular and highly infiltrative proliferation of spindle cells over the full thickness of the gastric wall. Although the spindle cells grew mainly in the submucosa, they penetrated the muscularis propria, leaving intact muscle tissue that formed an irregular, island-like pattern, and reached the subserosa. The cells were identified as myofibroblasts by light microscopy, immunohistochemistry and electron microscopy. The present case is considered to be of an inflammatory pseudotumor due to extremely infiltrative growth of myofibroblasts. This lesion differed from inflammatory fibroid polyp (similarly consisting of proliferating myofibroblasts accompanied by inflammatory cells) in terms of age at onset, tumor size, pattern of cell proliferation and main inflammatory cell component. This report also discusses the relationship between this lesion and a very recently advocated new entity, inflammatory fibrosarcoma of the mesentery and retroperitoneum, which is a tumour closely simulating inflammatory pseudotumor.