Follow-Up or Forget It? Managing Indeterminate T1-Hypointense Spine Lesions

Let's talk about an imaging finding that we encounter not uncommonly.

You're reading a spine MRI, and there is a small vertebral marrow lesion.

It's low signal on T1 weighted imaging, maybe a little bright on fluid-sensitive sequences, but there are no clearly aggressive features.

And then comes the question: What do we do with it? Do we call it indeterminate and recommend follow-up? Do we get a CT? Does the patient need another MRI and another MRI? And perhaps more importantly, how worried should we be, uh, about malignancy? And that's the clinical dilemma this study tries to address.

We know that intrinsically T1 hyperintense vertebral lesions are almost always benign outside of the uncommon hemorrhagic or proteinaceous metastases.

Low T1 signal lesions, however, are much less straightforward.

The differential is broad and includes, you know, benign osseous lesions, degenerative disease, focal red marrow metastatic disease, and much less commonly, primary aggressive or malignant bone tumors.

The Society of Skeletal Radiology introduced the Bone Reporting and, uh, Data System or Bone RADS in 2022 to provide a framework for managing incidental bone lesions.

But those guidelines were not specifically designed for the spine, and there has been relatively limited validation using MRI.

And more importantly, there really hasn't been any good longitudinal data telling us what happens to these indeterminate, uh, low T1 signal vertebral lesions over time.

So the authors asked a very practical question: When a vertebral lesion looks indeterminate on MRI but lacks aggressive imaging features, how often does it actually turn out to be malignant? This was a retrospective study of spine MRI lesions performed between 2017 and 2025 in which an osseous lesion had been specifically reported as indeterminate.

The authors initially reviewed 538 exams with 278 lesions ultimately meeting the inclusion criteria as you can see in Figure 1.

Patients with known osseous metastatic disease were excluded, and for each lesion, the authors evaluated the MRI signal characteristics and available follow-up imaging.

And the lesions were classified according to their eventual outcome, such as stable for at least two years, or unchanged on shorter follow-up, follow-up between two and 24 months, uh, or characterized as benign or degenerative on subsequent CT or MRI, or ultimately malignant.

The authors also stratified patients according to their cancer history, including those with no known malignancy or known malignancy without metastatic disease and patients who were subsequently found to have metastatic disease.