FL usually involves enlarged lymph nodes populated by abnormal follicles (see adjacent picture) that when examined histologically contain a mixture of centrocytes or centroblast surrounded by non-malignant cells, mostly T-cells. The centrocytes, which typically outnumber centroblasts, are small to medium-sized B-cell lymphocytes that characteristically exhibit cleaved nuclei; the centropblasts are larger B-cell lymphocytes without cleaved nuclei. Rare cases of FL may show lesions that contain tissue infiltrations dominated by B-cells with features of precursor (i.e. "blast") cells, monocytes, or malignant mantle cells such as those found in mantle cell lymphoma. Immunochemical analyses reveal that these cells generally express B-cell surface markers including the CD10 (60% of cases), CD20, CD19, CD22, and CD79 but not CD5, CD11c, or CD23 cell surface proteins; genomic analyses reveal that these cells contain t(14:18)(q32:q21.3) translocation (85-90% of cases), 1p36 deletions (60-70% of cases), and with far less frequency the other genomic abnormalities listed in the above sections on Pathophysiology and Presentation and course. None of these protein markers or genomic abnormalities are diagnostic for FL, e.g. the t(14:18)(q32:q21.3) translocation is found in 30% of diffuse large B-cell lymphoma and in a small number of reactive benign lymph nodes. Rather, the diagnosis is made by a combination of histological, immunological, and genomic abnormalities. According to World Health Organization (WHO) criteria, differences in the microscopically determined morphology of these tissues can be used to diagnose and categorized FL into the following 3 Grades with grade 3 having A and B subtypes:

Grade 1: follicles have <5 centroblasts per high-power field (hpf).
Erythema induratum is a panniculitis on the calves. It occurs mainly in women, but it is very rare now. Historically, when it has occurred, it has often been concomitant with cutaneous tuberculosis, and it was formerly thought to be always a reaction to the TB bacteria. It is now considered a panniculitis that is not associated with just a single defined pathogen. The medical eponym Bazin disease was historically synonymous, but it applies only to the tuberculous form and is dated. Pathophysiology
Predisposing factors include abnormal amount of subcutaneous fat, thick ankles and abnormally poor arterial supply. Abnormal arterial supply causes low-grade ischemia of ankle region. The ankle skin becomes sensitive to temperature changes. When weather is cold, ankle is cold, blue and often tender. In hot weather, ankle becomes hot, edematous, swollen and painful. Chilblains may be present. On palpation, small superficial and painful nodules are felt. They break down to form small and multiple ulcers. Fresh crops of nodules appear in periphery of ulcer and ultimately break down. In nodular stage, pain is present; while it subsides in ulcerative stage. Diagnosis
Mainly clinical. Eponym
The name Bazin disease honors Pierre-Antoine-Ernest Bazin. Additional images
References
External links
 Media related to Erythema induratum at Wikimedia Commons
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