Giant cell tumour of sacrum

Clinical History

17-year-old male patient presented with progressively increasing low back pain and numbness in the toes of the right foot for the past 2 months. MRI of lumbosacral spine without gadolinium was obtained as screening investigation.

Imaging Findings

MRI revealed a large expansile lesion with extensive soft tissue component arising from sacral vertebrae and both sacral alae (Fig. 1). The mass showed heterogeneous low to intermediate signal intensity on T2WI with curvilinear area of low signal intensity on T1WI and T2WI (Fig. 2). Few small foci of high intensity on T2WI and STIR sequence were seen within the soft tissue mass in keeping with cystic or necrotic components. As the imaging findings were suggestive of a neoplastic mass of the sacrum, surgical biopsy and histopathological analysis were performed. Microscopy showed a neoplastic lesion composed of evenly dispersed giant cells interspersed with proliferating mononuclear stromal cells. Occasional mitosis was found. Findings were consistent with giant cell tumour.

Discussion

Giant Cell Tumour (GCT) is a relatively common skeletal tumour, accounting for 4%–9.5% of all primary osseous neoplasms and 18%–23% of benign bone neoplasms. GCT is typically benign and solitary. However, multiple lesions have been described and 5%–10% of lesions may be malignant. [1] It occurs most commonly in 3rd to 5th decades of life and affects both males and females with slight female preponderance. [2] The most common specific location of GCT is about the knee. The single most common site is the distal femur followed by the proximal tibia, distal radius, sacrum (4%–9%) and proximal humerus. [1]
Sacral lesions are frequently large with destruction of the sacral foramina, but this nonspecific finding is also observed with other large sacral lytic lesions. A sacral GCT commonly involves both sides of the midline, and an extension across the sacroiliac joint is frequent. This feature is infrequent in GCT of long bone as the epiphysis serves as barrier and limits invasion of the joint. [3] CT improves detection of cortical thinning, pathologic fracture, periosteal reaction and degree of osseous expansile remodelling compared with radiography. [1]
MRI of a GCT often show heterogeneous signal intensity on all pulse sequences. Generally, the tumour is of low to intermediate signal intensity on T1-weighted images (WI). Interestingly, GCT have low to similar signal intensity to the normal spinal cord on T2-WI. This reflects the relative collagen content of fibrous components and haemosiderin within the tumour. Although this feature is not unique to giant cell tumours of the spine, it is quite helpful in making a differential diagnosis because most other sacral neoplasms (metastases, myeloma, lymphoma and chordoma) show high signal intensity on the long-TR MR images. This appearance may be the initial imaging characteristic suggestive of a correct diagnosis. Evidence of recent haemorrhage may also be apparent with areas of high signal intensity on T1-WI and T2-WI or fluid–fluid levels on the MR images. Cystic areas (similar to those seen in aneurysmal bone cyst) and regions of old haemorrhage with haemosiderin deposits are common. [3] Intralesional curvilinear areas of low signal intensity have also been described previously in plasmacytoma and vertebral haemangioma. [4] A solitary bone plasmacytoma needs to be considered in a differential diagnosis. However, heterogeneous signal intensity on T2-WI heterogeneous enhancement, and cystic changes are unusual in vertebral haemangioma. [3] GCT shows a variable degree of enhancement on post contrast study. The patient is offered radiation therapy as large expansile sacral mass is amenable to complete excision.

Differential Diagnosis List

Final Diagnosis

Giant cell tumour of sacrum

URL:	https://www.eurorad.org/case/12953
DOI:	10.1594/EURORAD/CASE.12953
ISSN:	1563-4086