FDG PET/CT May Overestimate Red Bone Marrow Volume

Abstract 4405

Sambuceti, et al. (Eur. J. Nuclear Med Mol Imaging, Aug, 2012. 39: 1326–1338) used a computational FDG PET/CT model to estimate the volume of the bone marrow space and specifically “Red” or actively hematopoetic marrow in 102 nonmetastatic melanoma patients. 34.9 percent of all marrow space was estimated to be populated by “Red” Marrow. There was no associated pathologic bone marrow or peripheral blood count correlation of this FDG PET/CT model. In an attempt to define pathologic correlation of the findings of Sambuceti et al., 102 consecutive pathologic samples of femoral hip replacements were evaluated for their “Red” Marrow content and correlated with the patient's peripheral blood counts. The patients reviewed did not have active carcinoma or recent exposure to chemotherapeutic agents. 48/104(47.1%) of the samples obtained contained active “Red” Marrow”upon microscopic evaluation of femoral head and shaft samples stained with Hematoxylin and Eosin. Of these samples “Red' Marrow averaged 5.05 percent of the pathologic sample volume (range 0–40%) as opposed to 20–30 percent of the estimated bone marrow segmental space calculated to be populated by “Red” Marrow heads of long bones as defined by the FDG PET/CT model. In this study patient gender, height, BMI, weight, red marrow cellularity, peripheral white blood cell counts, platelets, hemoglobin, hematocrit, creatinine did not predict the extent of “Red” Marrow volume. Many variables may affect the results of these studies including: spotty metabolic activity of the marrow, clinical inflammatory effects of bone marrow in long bone heads, pathologic sampling errors, low study power, sample preparation and patient selection. Although there was no clear explanation for this overestimation of pathologic-FDG PET signal, the age of the populations were significantly different (55.9 years old in Sambuceti et al and 62.4 years old in this study). Age was found to have a significant correlation with “Red “Marrow volume in the Sambuceti et al study. The FDG PET scan evaluation may overestimate metabolic activity of “Red” Marrow and thus run the risk of obscuring other bone pathology. Therefore, prospective PET/CT-pathologic-clinical correlation studies are warranted in light of the prognostic, therapeutic, and diagnostic importance of “Red“Marrow activity in FDG PET/CT clinical staging of oncologic disease.