Case of the Month

FIG 1- Radiograph of the pelvis with both hips shows a soft tissue opacity in the right iliac fossa. There is erosion of the right SI joint and the right ala of the sacrum. The right hip joint is abducted and externally rotated. 

FIG 3A and 3B -There is displacement of the bowel loops and the bladder to the left.

Discussion

Telangiectatic osteosarcoma (TOS) is a rare variant of osteosarcoma accounting for 0.4-12% of all osteosarcomas (1).

The peak incidence coincides with the pubertal growth spurt.

Inactivation of p53 gene is one of the most important factors associated with osteosarcoma.

The most common clinical features include pain and swelling at the local site followed by pathological fracture and joint effusions. A few may present with metastasis at diagnosis.

TOS presents as a lytic destructive bone lesion. The metaphyseal region is the most common location but it can extend into the diaphysis and epiphysis.(2,3). The most common location is the metaphysis of long bones like distal femur, followed by proximal tibia, proximal humerus, proximal femur, pelvis, skull bones, and ribs (4).

On radiographs, TOS usually shows geographic bone destruction with a wide zone of transition. More permeative destruction is seen in other bone tumours.(2,3) The margins of the lesions are usually poorly defined, indicating aggressive growth. There is cortical destruction with soft tissue invasion(3,5).

On CT, low attenuating areas are seen within the lesion suggesting haemorrhagic components. Cortical irregularities and soft tissue mass associated with the bony lesion are common features(5,6).

On T1-weighted MRI, the lesion shows a heterogeneous low signal intensity, while T2-weighted image it has a high signal intensity due to the presence of cysts and haemorrhagic components (3,7). On MRI, it may show fluid-fluid levels within the lesion. While fluid levels are present in 95% of ABCs, they are seen in approximately 74% of osteosarcomas (3,7).

 The tumour usually contains multiple cystic spaces surrounded by thickened septae containing atypical cells. These septae can   show nodular or solid components and enhance on imaging (3,5).

The radiographic appearance of telangiectatic osteosarcoma can resemble other conditions like aneurysmal bone cyst and giant cell tumour. The presence of osteoid matrix in telangiectatic osteosarcoma helps to differentiate both. 

Definitive diagnosis is established by histopathological examination. Both ABC and telangiectatic osteosarcoma may show presence of blood-filled spaces lined by atypical stromal cells (2,8). Due to presence of cystic spaces core-needle biopsies may yield inadequate sample, resulting in false-negative results (6,7).  The criteria for diagnosing TOS include the identification of empty or blood-filled cystic spaces separated by septae, along with the presence of high-grade atypical cells. (8).

ABC is an expansive destructive, haemorrhagic, tumour-like condition and is a benign reactive vascular process. Mesenchymal stromal cells in ABC are benign in nature. Central giant cell granuloma and central giant cell tumour does not show large sinusoidal spaces.(9)

TOS is characterized radiologically and histologically based on - predominantly expansile lytic lesion with minimal sclerosis, grossly cystic medullary mass radiologically, and new bone formation with blood filled spaces lined by malignant cells with limited osteoid formation (9).

Accurate imaging interpretation is essential for proper diagnosis and treatment.

The sacral location possess additional challenges due to the complex anatomy and potential for misdiagnosis. The expansive growth pattern of TOS often leads to cortical destruction and soft tissue invasion, making surgical excision difficult. (7,10) 

The management of TOS typically involves a multimodal approach. Neoadjuvant chemotherapy followed by surgical resection remains the standard treatment protocol. Complete surgical resection is difficult due to the tumour’s infiltrative growth pattern and proximity to critical structures (5,10).

Achieving negative surgical margins is more difficult in TOS compared to other subtypes of  osteosarcoma (7,10)

Conclusion:

Telangiectatic osteosarcoma of the sacrum presents unique diagnostic and therapeutic challenges, considering its proximity to bowel and pelvic organs. Misdiagnosis of TOS as ABC may lead to diagnostic delay and poor treatment outcomes. Future research should focus on establishing standardized treatment protocols and exploring therapeutic options to increase survival rates.