# A Giant Baker’s Cyst in a Patient With Rheumatoid Arthritis: An Unusual Case

## TL;DR

A rare case of a very large Baker’s cyst in a man with undiagnosed rheumatoid arthritis is reported, highlighting the need for accurate diagnosis.

## Contribution

The novelty lies in documenting an exceptionally large Baker’s cyst in a patient with undiagnosed rheumatoid arthritis.

## Key findings

- A 24 cm longitudinal axis cyst was identified in the popliteal region via MRI.
- The cyst caused compression of adjacent structures and a mass effect on the medial gastrocnemius muscle.
- The case underscores the importance of timely diagnosis to manage such rare complications.

## Abstract

Baker’s cysts are fluid-filled swellings in the popliteal fossa commonly associated with degenerative and inflammatory joint diseases, including rheumatoid arthritis (RA), as well as with joint injuries. While they are usually small and asymptomatic, in rare cases, they can enlarge significantly and cause clinically relevant complications.

We describe the case of a 69-year-old man with an undiagnosed RA who presented at his first Internal Medicine consultation with a five-week history of progressive swelling in the left popliteal region extending to the mid-calf, accompanied by pain on movement and difficulty walking. Clinical evaluation revealed a large popliteal mass, and subsequent magnetic resonance imaging (MRI) confirmed a well-defined, heterogeneous cyst measuring 24 cm in its longitudinal axis, causing compression of adjacent structures and exerting a mass effect on the medial gastrocnemius muscle without evidence of rupture.

This case highlights the potential for Baker’s cysts to reach exceptional dimensions, emphasizing the importance of accurate diagnosis for appropriate management and treatment planning.