Osteoblastoma of the trapezium: A rare case report

Clinical History

A 16-year-old male patient presented with a 1-year history of progressive right wrist pain.
He visited other medical centres where he was treated for de Quervain's tenosynovitis.
The pain was located in the distal scaphoid pole, more intense at night and not related to trauma or manual activities.

Imaging Findings

Posteroanterior X-ray of right wrist shows an osteolytic lesion of trapezium (Fig. 1).
Magnetic resonance imaging (MRI) confirmed the presence of signal changes at scapho-trapezium (ST) articulation, soft tissue mass and inflammatory changes extending into the extensor tendons compartment. The differential diagnosis was made between benign and malignant tumour and inflammatory lesion. (Fig. 2 and Fig. 3).
A CT was also performed and confirmed the osteolytic lesion at scapho-trapezium articulation. (Fig 4, Fig. 5 and Fig. 6).
The Dual-Phased bone Gammagraphy study detected a moderate hypervascularization with osteoblastic increased activity on the right hand (Fig. 7).
Histological analysis of the trapezium showed connective tissue containing osteoid and primitive bone rimmed by osteoblasts next to numerous giant cells. There was no area suspicious for malignancy (Fig. 8).
The treatment was tumour curettage with allogenic bone grafting. (Fig. 9).
At 12-month follow–up evaluation, no recurrence was observed (Fig. 10).
The patient remains asymptomatic without limitations in his activities.

Discussion

Osteoblastoma represents 1% of all primary bone tumours [3] and is a rare pathology in the carpus, and has never been described in the trapezium to the best of our knowledge.

It affects men more than women with an incidence of 2-3:1, and more frequently patients younger than 30 years [2].

It is often seen in long bones, but it has a predilection for vertebral bodies.
Osteoblastoma is locally aggressive and resembles osteoid osteoma but it is larger in size (> 2 cm) and in contrast, pain is inconsistently relieved with salicylates [7, 4]. The pain is not intense and poorly localized, which can lead to a delayed diagnosis [1, 6]. Osteoid osteoma shows indeed the characteristic radiolucent nidus.

There are also differences in the natural history of both tumours: Osteoid osteoma tends to regress, while osteoblastoma is progressive and may undergo malignant transformation, although this still remains a controversy [8].

X-ray and CT are the "gold standard" for the diagnosis; CT examinations are best used to further characterize the lesion with regard to the presence of a nidus and matrix mineralization. However, when it presents with an aggressive pattern and soft tissue mass, MR is mandatory. Typical osteoblastoma has decreased signal intensity on T1 and variable on T2-weighted images. Due to calcified matrix, osteoblastoma can manifest as heterogeneously hypointense relative to marrow on non-fat-suppressed T2-weighted images [2].
Despite the fact that osteoblastomas accumulate radionuclide on bone scintigraphy studies, it is not specific [2].

For the differential diagnosis a percutaneous excisional CT-guided biopsy is appropriate. The histological characteristics between osteoid osteoma and osteoblastoma may be challenging. Both are osteoid formers but in the latter bone trabeculae are wider, longer and less cohesive [8].

Osteoblastoma easily recurs after incomplete surgical removal (around 20% of recurrence rate). Curettage and grafting are the treatments of choice and for recurrence en bloc resection with arthrodesis [3, 5]. A close monitoring of these patients is mandatory [2].

Osteoblastoma is an uncommon benign tumour, rarely found in the hand. So it should be recognized as a still possible cause of long term wrist pain.

For the diagnosis, plain films and CT examinations are the "gold standard", but for the more aggressive type, MR can be a useful tool.

Differential Diagnosis List

Final Diagnosis

Osteoblastoma

URL:	https://www.eurorad.org/case/10120
DOI:	10.1594/EURORAD/CASE.10120
ISSN:	1563-4086