Indeterminate T1-Hypointense Spine Lesions: Prevalence of Malignancy in the Absence of Aggressive Imaging Features

T1-hypointense bone lesions are commonly encountered on spine MRI and lack consensus for appropriate management. This study assessed the outcomes of indeterminate low-T-signal vertebral lesions to better inform follow-up management decisions.

This institutional review board-approved retrospective study was conducted on individuals who underwent a spine MRI between 2017 and 2025 on which an osseous lesion was reported as "indeterminate." Five hundred thirty-eight examinations were reviewed, and lesion signal characteristics and follow-up were collected. Lesions were categorized as stable, no follow-up, incomplete follow-up, benign or degenerative on CT/MRI follow-up, or malignant. A minimum interval of 24 months was required for stability, with incomplete follow-up defined as 2-24 months. Lesions were also classified as stable if a CT performed >2 years later demonstrated no change or no detectable abnormality. Cancer history was categorized as no known malignancy, prior or active malignancy without metastatic disease, and confirmed metastatic disease. Examinations were excluded if there was incomplete imaging or a known history of metastasis to bone.

Two hundred seventy-eight lesions met the inclusion criteria, of which 58% had ≥2 months' follow-up. Sixty-one percent were T1-isointense to skeletal muscle, 34% were hyperintense, and 5% were hypointense. Sixty-three percent of patients with follow-up had no malignancy history, and 9% had metastatic disease. Of lesions with follow-up, 55% were stable at ≥2 years, 33% were unchanged at 2-24 months, and 10% were typically benign or degenerative on follow-up. Three cases (2%) were malignant, all diagnoses of new bone metastases in the setting of known or concurrently diagnosed metastatic disease. All lesions were isointense to muscle on T1WI and hyperintense to marrow on STIR images.

Low-T1-signal bone lesions are typically benign in the absence of aggressive features or extraskeletal metastatic disease. Primary malignant osseous spine tumors are very rare, with none present in our cohort. The Society of Skeletal Radiology Bone Reporting and Data System suggested follow-up timing may not be appropriate for spine lesions, given the increased prevalence of both benign and metastatic lesions relative to primary bone tumors. Six to 12 weeks may be more reasonable follow-up timing when there is elevated concern for metastasis; follow-up may not be necessary in low-risk populations.