Pseudogout Causing Thoracic Outlet Syndrome

Abstract

Abstract Introduction/Objective Calcium pyrophosphate dihydrate (CPPD) crystal deposition or pseudogout is a common entity encountered in routine practice. However, when a common entity presents in uncommon locations with unusual clinical manifestations, it creates a diagnostic conundrum. Pseudogout commonly occurs in the joint extremities including knee, wrist, shoulder, hip, and ankle joints. The sternoclavicular joint is a rare site for pseudogout with very low incidence. To the best of our knowledge, there are only two other cases of pseudogout mimicking a tumor causing vascular obstruction in the literature. Methods/Case Report A 63 year old male presented with an enlarging supraclavicular mass. A computed tomography angiography scan of the chest revealed an irregular soft tissue mass located behind the medial clavicle measuring up to 4 cm and was noted to compress and partially occlude the right subclavian vein. Partial occlusion of right axillary vein, right internal jugular vein, and right brachiocephalic vein were also noted on imaging. The venous compression led to outflow obstruction and resultant recurrent deep vein thrombosis of the right upper extremity. Due to compression by the mass, he required stenting of the right subclavian vein which unfortunately reoccluded. Subsequently, the patient underwent excision of the mass and partial resection of the first rib with decompression of the thoracic outlet. The excisional biopsy revealed dense rhomboid-shaped CPPD crystal depositions in irregular nodules within a background of fibrinoid material and fragments of unremarkable cartilaginous tissue. The patients compressive symptoms were relieved following the excision. While clinically and radiologically the mass was concerning for a malignant tumor, histological examination provided a definitive diagnosis of a benign process. Results (if a Case Study enter NA) NA. Conclusion Pseudogout is a rare mimicker of bone and soft tissue tumors and differentiation from an enchondroma, or grade 1 chondrosarcoma becomes a challenge especially on small tissue biopsies and is a possible diagnostic pitfall.