Infrapatellar epidermal inclusion cyst

Case contributed by Ammar Ashraf

Presentation

Right knee swelling for a few weeks. No history of trauma or fever.

Patient Data

Age: 65 years
Gender: Male

Mild osteoarthritic changes at the knee joint. Small well-defined subcutaneous soft tissue swelling in the upper anterior leg at the level of anterior tibial tuberosity. 

ultrasound

A well-defined isoechoic ovoid shape soft tissue mass lesion measuring 2.7 x 1.2 x 2.6 cm, is seen in the subcutaneous soft tissues of the anterior upper leg. No calcifications, cystic components or internal vascularity is seen in it.

Findings: A well-defined cystic area with thick smooth fibrous wall, measuring 30 x 15 x 28 mm, is seen in the subcutaneous fat anterior to the ligamentum patellae at the level of tibial tuberosity (superficial infrapatellar bursa). It has low to intermediate signal on T1 and high signal on T2-weighted images. Grade II degenerative changes in the posterior horn of the medial meniscus. Degenerative changes at knee joint (articular irregularity, osteophytes, subchondral cysts along the medial femoral condyle and grade III chondromalacia patellae). Small knee joint effusion.

Impression: Pretibial superficial infrapatellar swelling, likely representing superficial infrapatellar bursitis; other possibility can be a sebaceous cyst

Post-operative x-ray

x_ray

Osteoarthritic changes at knee joint. Infra-patellar soft tissue swelling seen on the previous study is no more appreciable.

Case Discussion

Procedure: Excision of infrapatellar swelling. 

Diagnosis: Keratinous epidermal cyst.

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