Teaching point: The classic sonographic presentation of calcium pyrophosphate dihydrate crystal deposits in the Achilles tendon is reported.

A 71-year-old male presented to the emergency department (ED) for worsening right knee pain for the prior 3-4 weeks. Point-of-care ultrasound (POCUS) of the right knee showed a pseudo-double contour sign. Subsequent ultrasound-guided arthrocentesis of the knee joint was performed, and fluid studies showed the presence of calcium pyrophosphate crystals, which was consistent with pseudogout. Ultrasound for detection of calcium pyrophosphate crystals in pseudogout and chondrocalcinosis has sensitivity of 86.7% and specificity of 96.4% making POCUS a valuable tool for diagnosing crystalline-induced arthropathy in the ED.

A case of tophaceous pseudogout (i.e., calcium pyrophosphate dihydrate crystal deposition disease) in the temporomandibular joint (TMJ) extending into the cranium is reported. A 59-year-old woman was referred to hospital with swelling and pain in the left cheek, and with trismus. Computed tomography imaging revealed a large, granular, calcified mass surrounding the left condylar head, partly destroying the cortex of the condylar head, and extending into the cranium by destroying the glenoid fossa. Magnetic resonance imaging revealed that the soft-tissue mass was of low-signal intensity on T1- and T2-weighted images, and was enhanced after intravenous injection of gadolinium. The mass was clinically and radiographically suspected to be a neoplastic lesion or a synovial osteochodromatosis. However, histological analysis demonstrated that the mass contained granulomatous lesion due to multiple nodular deposits of numerous rod-shaped and rhomboid crystals, which verified the diagnosis of tophaceous pseudogout. The lesion was excised surgically using a preauricular approach. Neither radiographic nor clinical examination demonstrated any signs of mass recurrence in the long-term 8- and 14-year postoperative recall examinations. Tophaceous pseudogout is a rare benign arthropathy that presents with clinical and radiographic features mimicking neoplastic conditions of the TMJ. Therefore, it is recommended that tophaceous pseudogout is considered in the differential diagnosis when a calcified mass lesion of the TMJ is encountered.

Calcification in hyaline and fibrocartilage is caused by the deposition of calcium pyrophosphate dehydrate, commonly referred to as chondrocalcinosis. Clinically, this can lead to arthritis symptoms similar to a gout attack -"pseudogout". Nonetheless, also chronic or asymptomatic disease courses are possible. The prevalence of chondrocalcinosis increases with age. The diagnostic workup of degenerative joint disease, therefore, often reveals calcifications of articular cartilage as harmless incidental findings. However, particularly in patients younger than 60 years of age, chondrocalcinosis can be the symptom of an underlying metabolic disease. This review article highlights these rare diseases and presents unusual manifestations of chondrocalcinosis.