# Spherical coral-like synovial chondroma within a popliteal cyst: a case report

## TL;DR

A rare case of a coral-like synovial chondroma inside a popliteal cyst caused knee pain and limited movement, and was successfully treated with surgery.

## Contribution

This case report presents a previously unreported imaging appearance of synovial chondroma within a popliteal cyst.

## Key findings

- A spherical coral-like synovial chondroma was found inside a popliteal cyst, causing knee joint restriction.
- The unique morphology of the chondroma was not previously documented in medical literature.
- Surgical excision of the cyst and chondroma restored normal knee joint motion.

## Abstract

Popliteal cysts are common lesions, primarily characterized by soft tissue swelling, which may occasionally present with calcifications or small osteochondromas, and can rarely lead to restricted movement. We report a case involving a spherical coral-like synovial chondroma located within a popliteal cyst, which caused significant pain and limited the flexion and extension of the knee joint. Notably, the appearance of the synovial chondroma was strikingly similar to that of spherical coral, and its distinctive imaging features are previously unreported in the literature. Following the excision of both the popliteal cyst and the intra-cystic spherical coral-like synovial chondroma, the patient’s range of motion in the knee joint returned to normal. The unusual morphology may arise from constrained growth within the cyst under pressure during joint movement, potentially influenced by the hyperuricemic microenvironment. Clinicians should consider synovial chondromatosis in the differential diagnosis of complex or calcified popliteal cysts.