Beware Overcalling Spinal Metastases in Patients with Known Primary Malignancy on Magnetic Resonance Imaging

Purpose or Learning Objective: (1) To understand the overall frequency of unexpected musculoskeletal (MSK) findings in retrospective reviews; (2) to describe the importance of a correct diagnosis of incidental bone lesion versus marrow infiltration, especially in a setting of known primary malignancy; (3) to introduce and improve characterization of spinal tumor mimics, such as focal marrow hyperplasia (FNMH), Schmorl's node, hemangioma, enostosis, and benign notochordal cell tumors (BNCTs); and (4) to discuss image optimization, novel magnetic resonance imaging (MRI) techniques, and the use of auxiliary imaging modalities.

Methods or Background: The overall frequency of unexpected MSK findings in retrospective reviews is ~ 2 to 10%; the prevalence of incidental findings on cross-sectional imaging is much greater. Therefore, it is important to understand that not all marrow lesions in the setting of known malignancy represent metastatic disease.

We explore the many potential bone metastasis mimics in known malignancy: FNMH, Schmorl's node, hemangioma, enostosis, and BNCTs. The background etiology, locations, incidences, and classical signs including occasional atypical imaging appearances in the spine are presented in detail, particularly referencing the differences in lytic and osteoblastic metastases with high-quality imaging examples.

Successful lesion characterization relies on optimizing imaging in the first instance including not relying on non-MSK dedicated imaging.

Results or Findings: We address and reference imaging techniques available to radiologists to aid successful lesional characterization:

1. Dedicated bone tumor MRI protocols of the spine are recommended that afford familiarity include T1-weighted sequences that are of most benefit when assessing marrow infiltration.

2. Novel MRI techniques lend further information in a lesional diagnostic work-up: diffusion-weighted imaging and its ability to detect restricted diffusion; chemical shift imaging or Dixon can detect microscopic fat within lesions as signal dropout.

3. Mainstream imaging such as computed tomography still has a place in complex cases with some benign/non-neoplastic lesions having characteristic features.

4. Hybrid metabolic imaging including specific lesion-specific radiotracers are used increasingly to assess for early bone disease.

Conclusion: To have a better understanding of potential spine bone metastatic mimics, their characteristic imaging features, and to recognize when to best optimize imaging assessment of these lesions reduces the risk of misdiagnosis, unnecessary intervention, and treatment, particularly in the setting of a known primary malignancy.

Publication History

Article published online:
26 May 2023