Pelvic bone giant cell tumour

Clinical History

A 55-year-old woman presented with pain in the left groin region.

Imaging Findings

An expansile geographic lytic lesion with a narrow zone of transition and cortical thinning was found involving the left acetabulum.
On MR images, the lesion showed predominantly low signal intensity at the T1 and T2-weighted images. No cystic component nor fluid-fluid levels were noted. Solid enhancement was seen after Gadolinium-Based Contrast Media administration.

Discussion

Giant cell tumour of bone (CGTB) is a relatively rare, usually benign, bone tumour, that can be locally aggressive and even metastasize to the lungs. They are typically solitary [1].
The vast majority of lesions occur after physeal closure and are typically seen in young adults, between 20 and 50 years of age [1].
Most of the tumours develop at the end of the long bones but may also occur in flat bones and apophysis [2].
Pelvic location is relatively rare, with the acetabulum appearing the commonest site [3].
CGTB consists of numerous multinucleated osteoclastic giant cells uniformly distributed amongst a proliferation of mononuclear stromal cells that express RANKL, which appears to be play an important role in the pathogenesis of these lesions. Tumours often contain haemorrhagic areas [2].
The typical imaging appearance is a geographic lytic lesion with a well-defined margin without surrounding sclerosis, often with mild bone expansion. The lesion typically abuts the articular surface. More aggressive features such as broader zone of transition, cortical thinning, cortical break-through and soft-tissue mass can also be present. There is no matrix calcification [1].
The degree of aggressiveness by imaging does not correlate with histology and does not appear to predict well either the risk of local recurrence or the development of lung metastases.
On T2-weighted images areas of low signal intensity are typically seen due to large amounts of haemosiderin, fibrosis or high cellularity [1].
Fluid-fluid levels might be seen due to secondary aneurysmal bone cyst (ABC) component, which has been reported in 14% of cases [4].
The presence of enhancing solid components helps differentiate CGTB with secondary ABC from primary ABC [1].
Surgery is the treatment of choice for resectable tumours. In general, intralesional curettage is usually recommended. Combination of curettage with bone cement (polymethylmethacrylate, PMMA) increases local control [5, 6].
In conclusion, GCTB shoud be considered in the differential diagnosis of pelvic bone lytic lesions, particularly when meeting the aforementioned epidemiologic and imaging features.

Differential Diagnosis List

Final Diagnosis

Pelvic bone giant cell tumour

URL:	https://eurorad.org/case/14294
DOI:	10.1594/EURORAD/CASE.14294
ISSN:	1563-4086