Idiopathic fibrosclerotic disorders and other inflammatory pseudotumors.
[focal myositis]
Fibroinflammatory disorders constitute heterogeneous clinical conditions whose cause and pathogenesis are largely unknown. Inflammatory pseudotumor has been applied in a generic sense to several of these disorders, which present as a mass displacing surrounding anatomic structures or leading to organ dysfunction secondary to compressive growth around the ureter(s), common bile duct, or great vessels in the mediastinum. The fibrosclerosing disorders of retroperitoneal fibrosis, sclerosing mediastinitis, sclerosing cholangitis, orbital pseudotumor, and Riedel thyroiditis are seemingly related in a clinical sense because there are well-documented cases of patients with two or more of these conditions and reports of these disorders presenting in family members. Although the pathogenesis of the fibrosclerotic disorders has not been elucidated, autoimmunity in the context of an established collagen vascular disease or the setting of inflammatory periaortitis in retroperitoneal fibrosis has been one suggested mechanism. In the course of the diagnostic evaluation of an individual with a suspected fibrosclerotic disorder, it is imperative to exclude an underlying infection or malignancy. This caveat is especially relevant to sclerosing mediastinitis as a presentation of histoplasmosis or to retroperitoneal fibrosis secondary to a sclerosing large cell lymphoma. Sclerosing mesenteritis has some clinical and pathological overlap with the fibrosclerotic disorders, but its nosologic and pathogenetic relationship is uncertain at this time. There are several other fibroinflammatory processes, such as focal myositis, inflammatory fibroid polyp of the gastrointestinal tract, calcifying fibrous pseudotumor, and sclerosing peritonitis, which are probably unrelated to inflammatory myofibroblastic tumor or the primary fibrosclerotic disorders.
