Image Quiz

Subclavian Vein Thrombosis, Brachial Plexopathy, and Sternoclavicular Pain and Popping in a Sixteen-Year-Old Boy (continued)

Answer: Osteochondroma of the medial part of the clavicle.


Fig. 2		 Fig. 2 Sagittal computerized tomographic scan of the medial part of the left side of the chest, demonstrating an osseous lesion projecting posteriorly from the medial aspect of the clavicle and confirming cortical and medullary continuity between the lesion and the host clavicle.

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A computerized tomographic scan demonstrated an osseous tumor that was located <5 cm lateral to the sternoclavicular joint and projected posteroinferiorly toward the first rib (Fig. 2). The cortical and medullary continuity between the lesion and the host clavicle favored the diagnosis of an osteochondroma, which is rarely found in the clavicle. Only 4 mm of space remained between the tumor and the first rib. These findings, combined with the known subclavian thrombosis and brachial plexopathy, suggested that an osteochondroma was creating a mass-effect compression of the adjacent subclavian vessels and brachial plexus. Besides the typical appearance of an osteochondroma, the computerized tomographic scan did not reveal an obvious cartilage cap or soft-tissue mass, which would otherwise have raised concern about malignant transformation.

The patient elected surgical decompression. An oblique clavicular osteotomy was performed distal and lateral to the lesion. Elevation of the medial clavicular fragment revealed a large, irregularly shaped osseous tumor compressing the neurovascular structures. After elevation of adherent soft tissues, the tumor was excised from the posterior aspect of the clavicle with an oscillating saw. The clavicular osteotomy site was reduced and was secured with lag screw-and-plate fixation (Fig. 3). The tumor measured 3.3 × 1.6 × 1.6 cm. The cartilage cap was small and without evidence of malignant transformation. The pathologic diagnosis was benign osteochondroma (Fig. 4).


Fig. 3		 Fig. 3 Radiograph, made three months after surgery, showing union with stable fixation at the site of the clavicular osteotomy.

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Fig. 4		 Fig. 4 Photomicrograph revealing some orderly organization of cartilage cells undergoing endochondral ossification (above), with an expected transition to trabecular bone (below). The cartilage cap was typical, small, and without evidence of malignant transformation (hematoxylin and eosin, ×4).

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Discussion

We have described a rare case of thoracic outlet syndrome, with axillary-subclavian vein thrombosis and brachial plexus compression, secondary to an atypical medial clavicular osteochondroma. The axillary-subclavian vein has a unique position in the thoracic outlet at the junction of three major anatomic structures: the neck, the shoulder girdle, and the thorax. Our patient's strenuous overhead work as a butcher probably exacerbated the thoracic outlet compression, causing depression of the shoulder girdle and scissoring the subclavian vein between the clavicular tumor and the first rib. An extrinsic anatomic compression mechanism is present in most cases of effort-induced subclavian thrombosis, or Paget-Schroetter syndrome. Anatomic sources of this extrinsic compression include congenital clavicular pseudarthrosis, cervical ribs, clavicular nonunion, clavicular malunion, hypertrophy of the scalenus anterior, hypertrophy of the subclavius, a prevenous phrenic nerve, abnormal insertion of the pectoralis minor muscle, clavicular tumors, and an abnormally small space between the clavicle and the first rib.

According to the Mayo Clinic registry, only 0.5% of about 750 reported solitary osteochondromas were located in the clavicle. Of the nine solitary clavicular osteochondromas that have been reported in the English-language literature, two developed in the medial third of the clavicle, one developed in the middle third, and six developed in the lateral third. In contrast to the lesion in our patient, both of the other medial clavicular tumors reported in the literature were asymptomatic. However, most lateral clavicular osteochondromas are symptomatic because of either extrinsic mechanical irritation of the rotator cuff or other mechanical alteration of shoulder girdle function. Filis et al. reported the case of a patient with thoracic outlet syndrome resulting from a lateral clavicular osteochondroma who was managed with extensive decompression, including tumor excision and anterior scalenectomy. We believe that primary bone tumors of the clavicle, albeit rare, should be added to the differential diagnosis of sternoclavicular pain and thoracic outlet syndrome. Our main conclusion based on this rare case is that effective imaging with radiographs, magnetic resonance images, and computerized tomographic scans of the thoracic outlet and the medial part of the clavicle must be performed when there is any doubt about the cause of thoracic outlet syndrome. In the case of our patient, there also could have been a diagnostic role for contrast-enhanced computerized tomographic imaging, which could have been used to directly visualize the osteochondroma that was compressing adjacent contrast-enhanced vessels.

Osteochondromas are thought to arise from either trauma or a deficiency in the perichondral ossification groove of Ranvier. Since this tumor arises in association with physeal growth, bones developing by means of intramembranous ossification, such as the skull, clavicle, and spine, are rarely involved. In humans, the clavicle represents a remnant of an ancestral dermal exoskeleton and serves to stabilize the shoulder girdle. Histologic studies of human embryos have indicated that the clavicular mesenchymal anlage ossifies primarily through two intramembranous primary ossification centers, appearing at six weeks and fusing at seven weeks. Both the sternal and acromial ends of the clavicle have articular cartilage, but, after birth, a secondary ossification center develops in the cartilaginous sternal end only. This medial (sternal) secondary ossification center and physis contribute almost 80% of the clavicle's longitudinal growth, whereas the primary ossification centers contribute little to the increase in clavicular length. This secondary ossification center unites with the rest of the clavicle by or before the twenty-fifth year. It seems plausible that an osteochondroma of the medial part of the clavicle develops from the physis associated with this secondary ossification center.

Reference

1. Mollano AV, Hagy ML, Jones KB, Buckwalter JA. Unusual osteochondroma of the medial part of the clavicle causing subclavian vein thrombosis and brachial plexopathy. A case report. J Bone Joint Surg Am. 2004;86:2747-50.