# Concavities of the margins of focal bone lesions on MRI: a retrospective study of 586 cases

## TL;DR

This study found that concave margins on MRI scans of bone lesions are more common in benign tumors like fibrous dysplasia and osteonecrosis.

## Contribution

The study introduces concave margins as a potential imaging marker for distinguishing benign from malignant bone lesions.

## Key findings

- Benign lesions and tumors showed significantly more concave margins than malignant ones.
- Osteonecrosis and fibrous dysplasia frequently exhibited two or more concave margins.
- Concave margins suggest a non-aggressive nature of focal bone lesions.

## Abstract

Except for a few specific lesions, the analysis of the margins of focal bone lesions with MRI has been largely overlooked in the literature. We observed that some lesions exhibited concave margins, suggesting a non-aggressive nature. This study aimed to determine whether concave borders are more frequently present in certain types of focal lesions of the long bones on MRI, particularly in benign lesions.

MRI examinations of 586 focal intraosseous lesions of the long bones were retrospectively reviewed. Each lesion margin was independently classified by two musculoskeletal radiologists as concave, non-concave, or cortical. The number of concave margins was analyzed according to the lesion type and its classification as tumoral (benign or malignant) or non-tumoral.

The study group included 15 different types of lesions (75.1% tumors, 24.9% non-tumoral lesions). The number of concave margins per lesion varied significantly by lesion type (p < 0.001). Benign lesions and benign tumors had more concave margins than malignant lesions (p < 0.001). All osteonecrosis lesions, 44.8% of fibrous dysplasia lesions, 20.8% of abscesses, 14.8% of chondroblastomas, 12.5% of Langerhans cell histiocytosis lesions, and 2.9% of metastases showed at least two concave margins. No lesions in the other groups had more than one concave margin.

Our study revealed that several intraosseous lesions tend to exhibit concave margins. The presence of at least two smooth and regular inward-curved margins was most commonly found in benign lesions and benign tumors, such as fibrous dysplasia.

This study shows that at least two smooth, inward-curved margins are more common in benign bone lesions and tumors and may help in recognizing fibrous dysplasia in non-fatty lesions.

Identifying concave margins may help in recognizing benign bone lesions and tumors.Concave margins are mainly observed in osteonecrosis and fibrous dysplasia.Concave margins suggest a non-aggressive nature of focal bone lesions.

Identifying concave margins may help in recognizing benign bone lesions and tumors.

Concave margins are mainly observed in osteonecrosis and fibrous dysplasia.

Concave margins suggest a non-aggressive nature of focal bone lesions.