USEFUL INTERNAL STANDARDS FOR DISTINGUISHING INFILTRATIVE MARROW PATHOLOGY FROM HEMATOPOIETIC MARROW AT MRI

The objective of this study was to establish internal standards on MRI differentiating infiltrative marrow pathology from hematopoietic marr ow, The T1-weighted images of 74 patients (51 biopsy-proven; 23 clinic al follow-up) were reviewed retrospectively The relative signal intens ity of bone marrow was compared to adjacent skeletal muscle (n = 65) a nd/or nondegenerated intervertebral disk (n = 53). Twenty foci were hy perintense compared to muscle, of which 17 (85%) cases represented nor mal red marrow (P < .0001); 45 were isointense or hypointense compared to muscle, of which 44 (98%) represented infiltrative marrow processe s (P < .0001), Twelve were hyperintense compared to disk, of which 12 (100%) represented normal red marrow (P < .0001); 41 were isointense o r hypointense compared to disk, of which 40 (98%) represented infiltra tive marrow processes (P .0001). On T1-weighted spin-echo MRI, skeleta l muscle and intervertebral disk may serve as internal standards for d ifferentiating infiltrative pathology from normal hematopoietic marrow , Marrow lesions that are relatively isointense or hypointense to musc le and/or disk should not be considered normal hematopoietic marrow.