Duplication of clavicle, poorly understood and a very rare incidental congenital anomaly: Radiographic and multislice CT demonstration

Clinical History

The patient presented with swelling in the region of left shoulder of long duration. He did not have restriction of movements or history of trauma. His concern was cosmetic. On palpation the bony swelling was mobile and hard. There was no restriction of movements, muscle bulk and power was normal.

Imaging Findings

Radiographs obtained in antero-posterior and axial view showed well defined cortical bone below the clavicle overlying the coracoid process (Fig. 1). Isotropic CT examination with additional volume rendering and reformatted images showed a well defined cortical bone 22.4 x 9.2 mm below the clavicle (Fig. 2, 3). The lateral end of the bone was rounded and the medial end was articulating with the coracoid process (Fig. 4). There was no osseous connection with clavicle, sternum or neighboring ribs.
Features suggestive of duplication of clavicle: os subclaviculare was reported.

Discussion

The clavicle is the first bone to begin the process of ossification during development of the embryo, during the 5th and 6th weeks of gestation. However, it is one of the last bones to finish ossification, at about 21–25 years of age. It forms by intramembranous ossification. Even though it is classified as a long bone, the clavicle has no medullary cavity like other long bones. It is made up of spongy bone with a shell of compact bone. It is a dermal bone derived from elements originally attached to the skull.
The whole clavicle develops from a cartilaginous anlage. In the middle part of the clavicle, an osseous cuff develops very early by the ossification in the perichondrium. In the lumen of this cuff, a cartilaginous cork persists which is resorbed and replaced by bone and marrow later than in other bones. It is possible that cartilaginous nests may persist in the middle part of the clavicle. Duplication of the clavicle has been reported in the literature [1-6]. The first accounts in the literature were incidental radiographic findings attributed to an embryological phenomenon [2-4]. Golthamer [3] described the incidental finding of a supernumerary bone just below the clavicle and termed it “os subclaviculare”. He reported this as a congenital anomaly and clinically insignificant. Twigg and Rosenbaum [2] reported a “bifid” clavicle in a 40-year-old man. They concluded that this was an anatomic variant, “Without clinical significance and of purely anatomic interest”. Oestreich [4], suggested that partial clavicular duplication was developmental, but that one variety of the lateral clavicle hook could be an acquired lesion or occur congenitally [4].
Ogden [5] described a traumatic aetiology and stated that it was likely that the early reports occurred as the result of unrecognised injuries. In a skeletally immature person, the clavicle is enclosed in a thick periosteal sleeve. The physis of the bone is inherently weaker than the acromioclavicular joint ligaments and trauma to the shoulder usually results with a fracture instead of an acromioclavicular joint sprain. After the resulting injury, a new clavicle can form if the proximal clavicle remains displaced. New growth occurs from the distal epiphysis and toward the proximal diaphysis. The final result is a duplicate clavicle [5]. All authors have agreed that duplicate clavicles are clinically insignificant [6].
This case report illustrates the utility of volumetric CT scanning in showing the anatomical details of rare congenital anomalies and its anatomical relationship with neighboring mileu.

Differential Diagnosis List

Final Diagnosis

Duplication of clavicle: os subclaviculare

URL:	https://www.eurorad.org/case/9376
DOI:	10.1594/EURORAD/CASE.9376
ISSN:	1563-4086