PET-CT standardized uptake values are increased in focal nodular marrow hyperplasia: a review of indeterminate marrow lesions at a large teaching hospital

Focal nodular marrow hyperplasia (FNMH) is a benign entity that can create diagnostic uncertainty for the radiologist and, if not recognized, can lead to unnecessary intervention or cause interruption in potential treatment due to the need for follow-up imaging for clarification. Current research suggests lesions with a standardized uptake value over 3.6 on fluorodeoxyglucose positron emission tomography and CT scans should be considered metastatic rather than benign. The aims of this study are to analyze the multimodality characteristics of FNMH, educate the reader, and recommend imaging techniques to improve specificity in the absence of histological analysis. Patients who underwent cross-sectional imaging and nuclear medicine studies between 2018 and 2023 were collected, after concerns were raised as to the nature of indeterminate bone marrow lesions. Data were collected on demographics, malignancy, site of index lesion, imaging characteristics, and follow-up. A total of 9 eligible patients were collected. All patients underwent CT and MRI scanning. 8 of the 9 had Positron emission tomography CT (PETCT), of which 7 had standardized uptake values for PETCT exceeding 3.6 using different radiotracers. All but one of the cases were conservatively managed; the remaining case received radiotherapy to their lesion. FNMH can demonstrate higher PET standardized uptake values (SUV) than previously reported in the literature. This has important implications for treatment as the SUV overlaps with those of metastatic bony lesions. Work is needed to improve the distinction between benign and malignant lesions that lie at this threshold of uptake level.