A 29-year-old man presents at the radiology department complaining of low back pain since 4 months, not radiating to the leg. There was no history of trauma.
Digital radiography revealed increased density of the left iliac wing (Figure 1).
Computer Tomography (CT) was performed in the same week of the radiograph, confirming sclerosis of the left iliac bone. A sunburst periosteal reaction and osteoid matrix formation in the adjacent soft tissue were seen with extension into the sacroiliac joint (SIJ) (Figure 2).
On Magnetic Resonance Imaging (MRI), the bone marrow of the left ileum was hypo-intense on T1- and T2-weighted images (WI). A large heterogeneous soft tissue component was seen on fat-suppressed (FS) T2-WI, FS T1-WI and T1-WI without FS. Diffusion-weighted imaging (DWI) showed diffusion restriction at the periphery of the lesion. After administration of gadolinium contrast, there was enhancement of the non-mineralised component. Transarticular involvement of the SIJ was seen (Figures 3a, 3b, 3c, 3d and 3e). Neo-adjuvant chemotherapy was started, followed by surgical hemi-pelvectomy and partial resection of the sacrum.
Histopathology confirmed the imaging diagnosis of osteosarcoma.
Osteosarcoma (OS) is the most common primary bone tumour in adolescents, with a slight male predominance. Osteoid matrix formation is characteristic. OS typically occurs in the metaphysis of the long bones, with the knee being the most frequent localisation. Epiphyseal extension and joint involvement are common [1].
Primary involvement of the iliac bone is less common. Tumours located next to the SIJ need a precise evaluation with respect to their relationship to the joint, as this has a significant implication on surgical management. As a general rule, the synovial part of the joint constitutes a barrier, and extension will preferably occur through the ligamentous part of the joint [2]. However, aggressive tumours such as OS will occasionally extend through the synovium.
Non-specific pain and local swelling are usually the first signs of OS. Pathological fractures may also occur.
Radiography is the initial imaging modality of choice. Usually, the osteoid matrix production is sufficient to result in a cloudy moth-eaten area of increased density. Cortical destruction, with often extension into the soft tissues and aggressive periosteal reactions such as Codman triangle, onion skin and sunburst, is readily seen in long bones on radiographs but is far less evident in areas with a complex anatomy and superimposition such as the axial skeleton [1]. CT may play an additional role in detection and characterisation on these locations.
MRI is pivotal in local staging, evaluation of soft tissue extension and articular involvement. T1-WI is the most accurate sequence for the evaluation of tumour extension, which is often overestimated on T2-WI [3]. The osteoid matrix is of low signal on both T1- and T2-WI. DWI complements conventional T1- and T2-weighted imaging by early detection, adequate assessment of tumour extension and follow-up after therapy. Solid components enhance after administration of gadolinium contrast.
Histopathology is required for the final diagnosis. Different histological subtypes are identified depending on the dominant matrix. Sometimes the osteoid matrix is very subtle or cannot be seen macroscopically, which can make differential diagnosis very difficult [2,4].
The differential diagnosis with Ewing sarcoma is important, as it is more common in the pelvis than osteosarcoma. Ewing sarcoma usually presents with a larger soft tissue component and lacks osteoid matrix, although reactive bone formation is possible, which can make histological differentiation challenging [4].
Treatment consists of surgical resection and chemotherapy. Neo-adjuvant therapy is initiated for tumour volume reduction prior to surgery if limb-sparing approach is feasible [3].
Written informed patient consent for publication has been obtained.
Osteosarcoma
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Based on the provided X-ray, CT, and MRI images, a lesion is identified in the right iliac region, with the following characteristics:
Considering the patient’s age (29 years old), symptoms (persistent lower back pain for 4 months, no significant history of trauma), and imaging findings, possible diagnoses and differential diagnoses include:
Based on imaging findings (osteoid matrix formation, bone destruction, and soft tissue involvement) and the patient’s pathological examination results, the most likely final diagnosis for this lesion is:
Osteosarcoma.
If pathological confirmation has not yet been obtained, a further biopsy or consultation with a bone tumor specialist is recommended to establish a definitive diagnosis.
The primary treatment options for osteosarcoma include:
Rehabilitation/Exercise Prescription Recommendations:
This report is based solely on the provided images and related information for academic and reference purposes and is not a substitute for in-person consultation or the medical advice of a licensed physician. If you have any questions or changes in your condition, please seek professional medical services immediately.
Osteosarcoma
