Imaging Analysis for Metastatic Risk Assessment in Adamantinoma: The Aid of Radiology in the Absence of a Histological Grading—An MRI-Based Risk Model Proposal

<b>Background:</b> Adamantinoma is a very rare primary malignant bone tumor. A histopathological grading is still lacking, and as a result, metastatic risk stratification at diagnosis is challenging. Due to this, imaging could play a role in prognosis prediction and treatment strategy assessment. We aimed to evaluate baseline imaging features and their correlation with the development of metastatic disease. <b>Methods:</b> We retrospectively collected clinical (metastatic disease) and radiological data at baseline (Conventional Radiography, CT, MRI) of all consecutive patients with a histopathological diagnosis of adamantinoma at our sarcoma center between 2006 and 2022. Tumor location, dimensions, main radiological pattern (lytic, sclerotic, mixed), Lodwick-Madewell grading, periosteal reaction, multifocality, soft-tissue extraskeletal component, peritumoral edema, peritumoral enhancement, and vascular invasion were analyzed. Associations between the above-mentioned radiological features and metastatic disease at diagnosis or during follow-up were assessed. <b>Results:</b> Twenty-two patients were included (15 [68.2%] women, median age 27 years old, range 7-58 years old). Six out of twenty-two patients (27.3%) developed distant metastases (only two of them were dedifferentiated adamantinoma): two patients (9%) presented with metastatic disease at diagnosis, while four patients developed metastases during follow-up (18.2%). The following radiological features represent a significant risk for metastatic disease (<i>p</i> = 0.01): (i) presence of an extra-skeletal component (Odds Ratio [OR] = 75.40; 95% CI = 3.15-1802.71), (ii) vascular invasion (OR = 121.00; 95% CI = 4.28-3424.73), (iii) diffuse peritumoral edema (OR = 75.40; 95% CI = 3.15-1802.71), (iv) peritumoral enhancement (OR = 84.33; 95% CI = 2.93-2423.26). All other features analyzed were not significantly associated with the onset of distant metastases. Based on these above-mentioned MRI features, we built two risk models for metastatic disease (excluding peritumoral enhancement, which was not available in five patients, to be applicable on unenhanced MRIs): Model (A) = simultaneous presence of two of those three features (2/3) with a sensitivity of 100% (54.07-100%) and a specificity of 93.75% (69.67-99.84%). Model (B) = simultaneous presence of all three features (3/3) with a sensitivity of 83.33% (35.88-99.58%) and a specificity of 100% (74.1-100%). <b>Conclusions:</b> An accurate evaluation of baseline imaging studies (particularly MRI) in patients affected by adamantinoma may significantly aid in prognosis prediction and the selection of high-metastatic-risk patients. For these patients, strict follow-up controls and more aggressive treatments should be suggested after multidisciplinary discussions in sarcoma centers.