Fibrosing mediastinitis

(Panel A) Mediastinal adipose tissue (A) and lymph node (arrow) are intimately admixed with the fibrosing process at upper right and lower left. Hematoxylin and eosin, ×4.
(Panel B) A low power survey shows a broad area of fibrosis, with a less cellular area (top half) adjacent to a more cellular area at bottom. Hematoxylin and eosin, ×7.6.
(Panel C) The more cellular area contains spindled mesenchymal/fibroblastic cells, and small lymphocytes, all in a densely sclerotic background. Hematoxylin and eosin, ×20.
(Panel D) The collagen is often present in alternating bundles of finely fibrillar collagen (pale) and coarser, more dense fibrils (darker). Note the focus of small lymphocytes at upper left (thick arrow). Hematoxylin and eosin, ×20.