Focal nodular marrow hyperplasia: Imaging features of 53 cases

Abstract

Objective: To describe the characteristic imaging features of focal nodular marrow hyperplasia (FNMH). Methods and materials: Retrospective review of all patients with a diagnosis of FNMH between January 2007 and September 2019. Results: The study included 53 patients, 7 males and 46 females with a mean age of 58 years (range 12–95 years). All had MRI with conventional spin echo sequences showing a poorly defined round/oval lesion with mild T1W iso/hyperintensity compared to skeletal muscle, low T2W turbo spin echo (TSE) signal intensity (SI) compared to marrow fat and variable SI on STIR, but never associated with reactive marrow oedema. All 53 patients had follow-up MRI, with all lesions remaining stable or partially resolving. In-phase (IP) and out-of-phase (OP) chemical shift imaging (CSI) was obtained in 31 of these, with 28 (90.3%) showing >20% SI drop on the OP sequence, while 3 (9.7%) demonstrated <20% SI drop. CT was available in 26 cases, 17 (65.4%) showing mild medullary sclerosis. Single-photon emission computed tomography CT (SPECT-CT) was available in four cases and Flourodeoxyglucose positron emission tomography CT (FDG PET-CT) in 2, all showing increased uptake. Focal uptake was also seen in three of eight patients who had undergone whole body bone scintigraphy. Only one lesion was biopsied, confirming FNMH. Conclusion: The imaging appearances of FNMH have been described on various modalities, particularly MRI with emphasis on the role of IP and OP CSI typically demonstrating >20% SI reduction. FNMH should be recognised and treated as a 'do not touch' lesion which does not require biopsy or prolonged follow-up. Advances in knowledge: We describe and clarify the imaging characteristics of FNMH on MRI, including CSI, CT and various nuclear medicine modalities. An imaging algorithm is suggested for allowing a non-invasive diagnosis.

The Dixon method in musculoskeletal MRI: from fat-sensitive to fat-specific imaging

“…It is important to note that some normal variants of bone marrow (including red marrow islands and focal nodular marrow hyperplasia), as well as some signal abnormality patterns such as bone marrow edema-like signal (usually non-neoplastic in nature), are also hypointense relative to normal bone marrow on T1w sequences [5,6]. However, because these non-bone marrow-replacing lesions usually contain fat, their SI is not quite as low as that of bone marrow-replacing lesions.…”

Current progress and future trends in imaging of musculoskeletal bone tumours

“…Along these lines, another study found that the T2w dixon fat only images provided significantly more contrast than the standard T1w sagittal image for detecting multiple myeloma spinal lesions. 19 Nevertheless, Heynen et al 20 showed that T2w dixon sequences are less sensitive than standard T1w sequences in detecting hip and pelvic occult fractures. The T1w sequence still remains as the current gold standard sequence in identifying areas of marrow infiltration, showing lower signal compared to the surrounding skeletal muscle.…”

“…The T1w sequence still remains as the current gold standard sequence in identifying areas of marrow infiltration, showing lower signal compared to the surrounding skeletal muscle. 20 Chemical shift imaging also provides a useful means for identifying areas of focal nodular marrow hyperplasia (FNMH) which can mimic a bone tumour/metastases. 20 This is especially useful in the setting of known primary malignancy where the patient presents with an 'indeterminate,' lesion.…”

“…20 Chemical shift imaging also provides a useful means for identifying areas of focal nodular marrow hyperplasia (FNMH) which can mimic a bone tumour/metastases. 20 This is especially useful in the setting of known primary malignancy where the patient presents with an 'indeterminate,' lesion. The traditional approach has been to either follow up these lesions or to biopsy, carrying an unnecessary risk.…”

“…FNMH tends to exhibit iso-hyperintense T1 signal compared to surrounding skeletal muscle, with at least 20% signal drop on OOP sequences. 20…”