PELVIC MARROW IN ADULTS

The appearance of hematopoietic marrow in magnetic resonance (MR) imag ing is variable and differences between normal and pathologic marrow m ay be subtle. To aid in the evaluation of this problem, we reviewed 82 consecutive pelvic MR examinations in men with no evidence of osseous metastases. Images were evaluated with regard to the overall fraction of residual hematopoietic marrow present and the characteristics of t his marrow. The patient population in our study was older (mean age 66 years) than the patient populations in previous papers documenting no rmal marrow patterns The overall amount of hematopoietic marrow presen t was less in this older patient population, with 80% of patients havi ng less then 40% residual hematopoietic marrow. A consistent pattern o f morphologic change was noted as hematopoietic marrow converted to fa tty marrow with increasing age. Initially, hematopoietic marrow tended to appear diffuse, heterogeneous, and with poorly defined margins on MR imaging. As conversion to fatty marrow continued, hematopoietic mar row became more focal and sharply defined, usually in the form of isla nds of residual hematopoietic marrow. Periarticular hematopoietic marr ow predominated in the sacroiliac region (72% of patients) with little residual hematopoietic marrow noted in the symphysis pubis (5%) and h ip joints (30%). Hematopoietic marrow persisted longer in juxtacortica l locations (87%), was always symmetric (100%), remained less intense than fat on T2-weighted images (100%), and usually had a central focus of fat (98%). These morphologic criteria may be of value in establish ing the MR appearance and patterns of marrow in the pelvis, and in the recognition and confident diagnosis of foci of hematopoietic marrow.