DISCUSSION:
First mentioned by Jaffe et al., PSC is a rare benign tumor affecting the synovial cavity [5]. It is a proliferation of multiple cartilaginous nodules in the synovium of joints, tendon sheaths, and bursae.
These nodules may break free from the synovial membrane to become cartilaginous loose bodies in the joint space [4,10,15,17-20].
According to the literature, this disorder usually occurs in men between the ages of 30 and 50 old-years. It has been reported that knees, hip, elbow, and wrists are the main affected joints in descending order of frequency [10,12,15]. The involvement of the shoulder is unusual in adults, and more exceptional during childhood. To the best of our knowledge, only five cases have been reported in the literature [4,7,12,14,16].
Based on the underlying pathogenesis, synovial chondromatosis may be primary or secondary. The PSC, called idiopathic synovial osteochondromatosis or Reichel syndrome, usually occurs in a previously healthy joint.  In contrast, secondary osteochondromatosis is a sequela of intra-articular pathology as osteochondral fracture, osteochondritis dissecans, and osteoarthritis [4,9,7,11,15,20]. In our case, the young-onset, the absence of a history of trauma, and the unremarkable results of blood tests strengthen the diagnosis of PSC.
It is noteworthy that histopathologic analysis is mandatory to distinguish between these conditions. [4,6,10,15,19]. In a series of 136 presumed synovial osteochondromatosis, Villain et al showed that the histopathological patterns are different. In fact, in primary lesions, the foci of chondrometaplasia in both synovium cells and loose bodies are noticeably disorganized. The chondrocytes are frequently binucleate, and the pattern of calcification is patchy and diffuse. However, in secondary lesions, calcification is zonal and uniformly distributed, and fragments of articular cartilage or subchondral bone are usually in the loose bodies [19]. In the present case, histologic evaluation revealed multiple cartilaginous nodules arranged in clusters and embedded in synovium.
Clinical presentation is often nonspecific [7,15,17]. As a result, patients may experience long symptoms delays before the final diagnosis. Like the current case, most children with PSC of the shoulder were diagnosed between 10 to 14 years old with a diagnosis delay ranging from 1 to 18 months from symptoms onset [4,7,11,12,16].
In a recent literature review of cases with osteochondromatosis occurring in the shoulder, the most common reported symptoms were mainly shoulder pain, uncomfortable feeling during exercises, and locked joint movement [18].  Our report is following data in the literature. Interestingly, a palpable bony mass may occur, as described in two children with PSC of the shoulder [3,20].
Radiographic features vary according to the degree of ossification. In the later stages of the disease, the plain radiographs showed a characteristic image with multiple intraarticular radio-opacities. These calcifications are frequently very similar and uniform in size with a typical nest-like arrangement. Thus, plain radiographs may be normal in the earlier stages (30% of cases) [3,20]. Sometimes, the diagnosis overlaps between differential diagnostics such as osteosarcoma and chondrosarcoma.
Hence, MRI plays a pivotal role in confirming the diagnosis by revealing intra-synovial hypo-intense nodules on T1 and T2-weighted images. MRI also aids in the management of surgical approaches. [2,3,5,17,18].
The optimal therapeutic management of the disease requires surgical removal of any loose bodies [7,8,13,16,17]. Partial synovectomy, optional but often recommended, may decrease the recurrence rate [15,16,20]. Histopathological analysis of the loose bodies and synovial tissue is mandatory as a malign transformation may occur in up to 5% [1,7,17]. The choice of surgical procedure is still a matter of debate [15]. Open surgery remains the mainstay of treatment and is highly recommended in cases of osteochondromatosis with soft-tissue involvement and limited anatomic space access [7].  Moreover, this approach was often preferable in pediatric patients with shoulder involvement [7,12,14,16].On the other hand, the arthroscopic surgery approach may offer less morbidity and earlier postoperative recovery [20]. In line with Hamada et al, we opted for shoulder arthroscopy using the deltopectoral approach [4].  To elucidate further the clinical presentation and the therapeutic management of PSC of the shoulder in children, we analyzed findings reported in the literature (Table 1).
According to the literature, recurrence is common and ranges between 15% and 30% [1,2,15,16].  It’s noteworthy to mention that no recurrence of calcification was reported among pediatric patients with PSC of the shoulder  [6,7,16]. However, close follow-up including imaging in the first two years is warranted [7,16]. In our case, the short duration of follow-up was not sufficient to make a definitive conclusion.
In sum, the present case illustrates a rare entity of PSC that combined the intra and extraarticular involvement of the shoulder. MRI is a powerful key for early diagnosis. The management of this affection, like in adult patients, is based on the chondromyxoid bodies remove through open or arthroscope-assisted surgery. Histological analysis is mandatory since that a malign transformation might occur. Prognosis is excellent, associated with a low-moderate risk of recurrence.