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Reticulin grade 3 (MF-3) in myelofibrosis is characterized by a diffuse and dense increase in reticulin fibers throughout the bone marrow, forming a coarse, widely interconnected and intersecting fibrillar network. There is often associated collagen deposition and possible osteosclerosis, contributing to marked architectural distortion and reduction of normal marrow spaces. In addition, there is increased extrafibrillar antigen deposition, which may show variable distribution; in some advanced MF-3 cases, type III collagen extension may be less extensive despite overall dense fibrosis, as highlighted in Gomori’s reticulin staining. Hematopoietic elements are significantly reduced or displaced, and the marrow may approach a fibrotic or “burnt-out” phase, reflecting advanced disease.