Hodgkin lymphoma with an interfollicular growth pattern: A clinicopathologic study of 8 cases.

Classic Hodgkin lymphoma (CHL) has four subtypes. Different morphologic variations can be seen in lymph nodes involved by CHL. Primary interfollicular (IF) involvement is not considered a separate subtype but an unusual diagnostically challenging morphologic variant. Our aim was to study the prevalence of IF growth pattern and coexistence of other morphologic variants in lymph nodes involved by CHL, to investigate the diagnostic challenges and clinical importance of this growth pattern, and to find helpful histologic clues in cases with subtle morphologic features to help avoid misinterpretation and missed diagnosis. We performed a retrospective review study over 10years. We searched for diagnosed cases of nodal CHL. We retrieved and reviewed cases of CHL with IF involvement. The clinical and pathologic features of each case were collected and compared. We found 103 cases of CHLs. Eight cases (7.8%) demonstrated IF growth patterns. The age range was between 3 and 48years with an average age of 26years. The male to female ratio was 7:1. Six cases were mixed cellularity HLs. Three cases had associated epithelioid granulomas, one had follicular involvement and one had an associated. HHV-8 negative plasma cell rich Castleman disease. One case was initially missed as benign follicular hyperplasia, one case was referred as CD and three cases were initially suspected as HL. IF growth pattern in nodal CHLs can be missed because it can be mild and focal with subtle morphologic features. The presence of epithelioid histiocytes, eosinophils and other coexistent morphologic variants are helpful histologic clues. In doubtful cases, immunohistochemistry study is essential. The majority were early stage cervical node MCHLs in young adults and children. Pathologists should be aware of this possibility when examining reactive lymph nodes. The clinical significance is limited and needs further validation by larger studies.