CASE 9409 Published on 04.09.2011

Osteosarcoma of the rib

Section

Paediatric radiology

Case Type

Clinical Cases

Authors

Ip J, Conceição e Silva JP

Instituto Português de Oncologia de Lisboa, Francisco Gentil
Portugal
Patient

6 years, male

Categories
Area of Interest Thoracic wall, Thorax, Bones, Musculoskeletal system, Oncology, Nuclear medicine ; Imaging Technique MR, CT, Conventional radiography, PET
Clinical History
6-year-old previously healthy boy presented with asymptomatic swelling on the left anterior chest-wall noticed by his mother as palpable well circumscribed mass the week before observation.
Imaging Findings
Chest X-ray (CXR) revealed an occupying-space-lesion located on the left anterior chest-wall adjacent to the 9-11th-ribs. Computed tomography (CT) showed an expanding 68x43mm-lesion, originating on the cortical of 8th/9th left anterior ribs with inhomogeneous density regarding small parts and calcium components with destruction. A biopsy confirmed mesenchymatous malignant tissue. Chest-CT served two purposes: as procedure-guided-biopsy and to evaluate lung metastases. He underwent chemotherapy prior to surgical resection. Bone scintigraphy demonstrated focal osteoblastic lesion involving 8th-10th-ribs. Positron Emission Tomography (PET) showed F18-FDG seldom uptake on left hemithorax. CT and magnetic resonance (MR) prior to surgery showed unchangeable lesion dictating poor therapeutic response. MR documented areas of low signal on T2-weighted images and T2SPIR and iso-hypointense signal on T1-weighted sequences in relation to areas of necrosis/fibrosis. No other sites were involved. The patient underwent surgical resection and pathology confirmed a rib osteosarcoma with 20% of necrosis, classified as poor responser to chemotherapy.
Discussion
Osteosarcoma is the first most common bone cancer in adolescence. It is thought to arise from a primitive mesenchymal bone-forming cell and is characterised by production of osteoid.
The most common locations are the limbs (femurs and humerus) and less frequent the skull, jaw and pelvis. The incidence is slightly higher in African Americans than in Caucasians with male predominance. The incidence of osteosarcoma increases steadily with age; a relatively dramatic increase in adolescence corresponds with the growth spurt and rarely occurs below the age of 5 years. Recent data show secondary involvement of 15–20% of patients with osteosarcoma of whom (85%) have pulmonary lesions as the sole site of metastasis. Outcome and survival rates are closely related to the following factors: chemotherapy response prior to surgery (>90% necrosis, <10% remaining tumour); metastatic involvement at time of diagnosis and margins after resection.

Plain radiograms are usually the first examinations because they have a low radiation dose, easily available and provide cost-effective information to address further investigation. It shows expanded bone lesions with lytic and sclerotic components, sometimes even soft tissue invasion and joint effusion is seen. CT shows cortex partially destroyed with invasion of the soft tissues. It can detect small amounts of mineralised osseous matrix that can be overlooked on plain radiograms. Medullary bone involvement inside the exostosis can be confirmed on MR. Pattern of bone response can be pure lytic or mixed (lytic and blastic). Extraosseous involvement is often present. Extent is preferably demonstrated on T1-W SE sequences over STIR as this can overestimate size because of the surrounding oedema. Contrast enhancement with gadolinium gives information about tissue avidity and shows necrotic/fibrotic areas. Tumour blood supply can be assessed on MR, particularly with STIR and Fat-Sat sequences or alternatively PD sequences.
MRI of the primary lesion is the best method for local staging as it shows the extent of intramedullary disease and tumour behaviour. Chest-CT is the more sensitive method in staging pulmonary metastases and plays an important role on bone destruction characterization.
Some studies demonstrated changes in signal intensity at MR after chemotherapy. The use of Diffuse Weighted Images (DWI) along with the ADC map is being evaluated as routine mean to predict chemotherapy response correlating with histological necrosis degree.
Nuclear Imaging shows increase uptake of radioisotope and scintigraphy confirms a seldom lytic lesion.

New studies are focusing on developing biochemical turnover markers in order to confirm diagnosis and predicting treatment responses.
Differential Diagnosis List
Rib osteosarcoma
Ewing sarcoma and primitive neuroectodermal tumors
Histiocytosis
Nonrhabdomyosarcoma soft tissue sarcomas
Rhabdomyosarcoma
Osteomyelitis
Final Diagnosis
Rib osteosarcoma
Case information
URL: https://www.eurorad.org/case/9409
DOI: 10.1594/EURORAD/CASE.9409
ISSN: 1563-4086

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