Fibrous dysplasia is one of the most common skeletal lesions. The wide spectrum of clinical manifestations ranges from asymptomatic conditions (typical of monostotic forms) to severe skeletal diseases with deformity and fractures for polyostotic fibrous dysplasia. The classical radiological features include: an osteolytic geographic pattern, ground-glass bone matrix, cortical thinning/cortical scalloping, bone deformities and enlargement, concavity of margins (evaluated with MRI), and cystic areas (MRI). All the bones can be affected, and the proximal femur is the most common one (about 30% of cases). Nonetheless, the disease can also affect cranio-facial bones, leading to compression of neural structures, as well as deformation and enlargement of facial bones, leading to the so-called “leontiasis ossea” or “facies leonine”. The polyostotic forms of fibrous dysplasia can be associated with multiple soft-tissue myomas (Mazabraud syndrome) or several endocrine diseases (McCune–Albright syndrome). In every diagnostic step of the disease, as well as in different fibrous dysplasia forms, imaging plays a key role. Indeed, radiology is fundamental to assess the suspicion of fibrous dysplasia in classical monostotic forms, representing the sole diagnostic tool needed in many cases. Imaging is also fundamental to staging and following up on more severe polyostotic forms, as well as for detecting complications. In this comprehensive updated review article, we examine every aspect of the disease, with a main focus on imaging presentation. The indications for biopsy are discussed as well. Most importantly, the article details the potential risk of malignant transformation (osteosarcoma, fibrosarcoma, chondrosarcoma, and other rarer sarcomas, all accounting for <1% of cases) underlying the radiological patterns of these conditions. The occurrence of aneurysmal bone cyst-like changes on fibrous dysplasia is also analyzed in the article. This review article aims to be a comprehensive guide for radiologists and clinicians involved in the care of patients affected by various forms of fibrous dysplasia, and a starting point for future research. Many classical and atypical cases are collected as an iconographic comprehensive representation.

Background/Objectives: Spinal epidural lipomatosis (SEL) is increasingly recognized as a possible radiological indicator of Metabolic Syndrome (MS) and visceral adiposity. However, the precise relationship between visceral adiposity and the accumulation of epidural fat (EF) remains unclear. This study aimed to investigate the association between visceral adipose tissue (VAT) and EF thickness using quantitative MRI analyses. Methods: We retrospectively reviewed all MRI scans performed at our institution over a 7-month period, from May to November 2024. Two radiologists measured and recorded the VAT maximum antero-posterior diameter at the L3 level, EF maximum diameter at the L5-S1 level, spinal canal antero-posterior diameter at the L5-S1 level, and subcutaneous fat (SF) when included in the MRI images (at the L3 level) in all the MRI scans. Results: A cohort of 516 patients was collected (320 women and 196 men; mean age 57.31 ± 18.45 years old). In 508 patients (98.4%) SF and VAT were both measurable, while in 8 patients VAT only was assessable on MRI scans. Pearson correlation identified significant associations between EF and VAT thickness (correlation coefficient > 20%; p < 0.05). A linear regression model confirmed a significant, albeit modest, positive relationship between VAT and EF (R² = 5.4%). A multivariate regression model incorporating age, sex, spinal canal size, VAT, and SF improved the explanatory power (adjusted R² = 16.7%), with VAT, spinal canal diameter, and age emerging as significant predictors of EF (p < 0.001). Conclusions: Our study revealed in a large cohort of patients that EF and VAT are directly associated. On the other hand, SF resulted in not being associated with EF. These findings support the emerging concept that SEL can be a radiological phenotype of visceral obesity and, by extension, of MS. Integrating EF measurement into standard MRI interpretation may facilitate the early detection of SEL and offer additional insights into patients’ underlying metabolic profile.

Background/Objectives: Osteosarcoma is a rare malignancy and the most common primary malignant bone tumor. Metastases commonly affect the lungs and are associated with reduced life expectancy. Calcifications can be present within a metastatic nodule at baseline or can appear during follow-up. We aimed to assess the clinical significance of calcifications in lung metastases, particularly in relation to radiological pattern, histopathological subtype, and treatment response. Methods: A retrospective cohort of patients with osteosarcoma and lung metastases at diagnosis was evaluated for the period 2000–2018. The presence of calcifications inside pulmonary lesions on baseline lung CT and/or follow-up was assessed and recorded. Radiological data were then checked against histopathological data (i.e., osteosarcoma subtypes and chemotherapy response with necrosis percentage) and the radiological pattern of the primary tumor (i.e., osteolytic, sclerotic, or mixed pattern). Results: Of a cohort of 92 patients, 14 were excluded due to having no baseline or follow-up chest CT. Of the 78 patients with an osteosarcoma diagnosis, lung metastases at diagnosis, and chest CT who were enrolled (42 men and 36 women; mean age: 23.8 years [range, 6–73 years]), 70 (89.7%) had a baseline imaging study of the primary tumor (osteosarcoma). The presence of calcifications in lung metastases at both baseline and follow-up was significantly associated with the radiological pattern of the primary lesion (p < 0.0001). Calcifications were not present in the lung metastases of any of the 18 patients (0%) with a lytic radiological pattern at any stage, whereas all 32 patients (100%) with a purely sclerotic pattern had calcifications within lung metastases at baseline or during follow-up; of the 20 patients with a mixed radiological pattern, 11 (55%) had no calcifications and 9 (45.0%) had detectable calcifications. No statistically significant association was found between histopathological subtype and calcification. Osteoblastic osteosarcoma was more frequently associated with calcification (66.0%). During induction chemotherapy, five poor responders and three good responders (necrosis > 90%) developed calcifications (p = 0.72; OR = 0.67; 95% CI, 0.10–3.86). Conclusions: In patients with osteosarcoma, calcifications within pulmonary metastases are strongly associated with the radiological pattern of the primary tumor, and this association is greatest for a pure sclerotic pattern, followed by the mixed one. We found no statistically significant association between the occurrence of calcifications during follow-up and chemotherapy response measured by necrosis percentage of the surgical specimen in our limited cohort; further research is needed.