Teaching Case

A 77-year-old male patient with newly diagnosed prostate cancer attends for a Tc-99m bone scan, which lead to the suspicion of humeral metastasis. The patient was asymptomatic, with a mildly raised PSA and had a normal bone profile.

Bone scan revealed faint focal uptake in the left proximal humerus (Fig. 1). Initial radiograph showed a 'sclerotic lesion' at the area of bone scan uptake (Fig. 2). Subsequent radiographs demonstrated gradual resolution of the sclerotic focus, with new focal lysis and mineralisation away from bone which was initially interpreted as periosteal reaction (Fig. 3, 4). The rapid radiographic evolution raised suspicions of humeral metastasis. Shoulder MRI showed a small ovoid area of altered signal in the anterior humeral cortex corresponding to the abnormality seen previously, but no marrow oedema or soft tissue mass (Fig. 5, 6). Subsequent CT of the humerus showed a corresponding well-defined concave cortical remodelling but nil else (Fig. 7). No metastases were seen on CT chest/abdomen/pelvis. All imaging was subsequently reviewed by regional MSK/sarcoma radiologists and the diagnosis of calcific tendinopathy of the pectoralis major was made, and not bony metastasis. Biopsy was deemed unnecessary.

Bony involvement is an uncommon, but well recognised, feature of calcific tendinopathy that may be confused with other pathologies, including malignancy [1-4]. The underlying pathophysiology is thought to be related to hypervascular inflammatory changes, with contributing effects of muscular traction, which induce focal resorption of the adjacent bone [3].

The tendinous insertion of the pectoralis major at the proximal humeral diaphysis is one of the commonest locations of calcific tendinopathy associated with osseous involvement [1]. To the best of our knowledge, this is the first report of pectoralis major calcific tendinopathy mimicking prostate cancer metastasis. The calcific deposit overlying the proximal humerus on the initial radiograph was misinterpreted initially as a sclerotic bony lesion. The rapid resolution of this, however, is unusual for a metastasis, but is often seen in the natural history of calcific tendinopathy. The remaining features of cortical erosion at the site of the pectoralis tendon insertion, mild uptake on scintigraphy and absence of a soft tissue mass are also recognised features of osseous involvement in calcific tendinopathy [1-4]. Although periosteal reactions have been reported in calcific tendinopathy [1], it was felt that the mineralisation away from bone seen in our case (Fig. 4) was perhaps more in keeping with calcific deposit within the pectoralis major tendon. More aggressive features that may be seen (not present in our case) include marrow oedema [1, 4] and enhancement of the surrounding tissues [4].

An important learning point from this case was the need to always obtain a second projection. Should a true lateral projection have been performed at the time of the initial radiograph, the reporting radiologist would have realised that the sclerotic lesion was not in fact intraosseous, but in the adjacent soft tissues, and thus would have avoided the need for subsequent MRI/CT to further investigate this.

Radiologists should be aware of the unusual appearances and sites of calcific tendinopathy, which in itself is a very common pathology. Biopsy was fortunately avoided in this patient, but if performed, chondroid metaplasia may be seen and the misdiagnosis of chondrosarcoma may be possible [4]. Recognition of this benign entity is therefore of utmost importance to avoid unnecessary biopsy with its inherent risks and patient distress.