Rare Knee Cyst Baffles Doctors: Atypical Case Study
Atypical cyst throws doctors for a loop, highlighting diagnostic challenges beyond common Baker’s cysts.
Rare Location
A recent case is spotlighting the challenges physicians face when diagnosing unusual masses around the knee. Typically, cystic lesions in this area are Baker’s cysts, but this case presented a surprise: an epidermal inclusion cyst in the popliteal fossa, the hollow behind the knee. Such cysts are more frequently found on the face, scalp, neck, and back, according to a report in Cureus.
Patient’s Experience
A 39-year-old man sought medical help for swelling behind his left knee, which had gradually increased over eight years. Though painless, save for mild discomfort during full knee flexion, the growth prompted an investigation to rule out more serious causes.
“Epidermal cysts were among the five most common skin diagnosis in the United States.”
Diagnostic Journey
Initially, doctors suspected a Baker’s cyst. However, an MRI revealed a well-defined lesion that didn’t connect with the knee’s deeper structures. This atypical presentation led to a surgical removal of the mass.
Histopathology Reveals
After excising the mass, a lab analysis confirmed it was, indeed, a benign epidermal inclusion cyst. The cyst measured 3×2.5×2 cm and was filled with soft tissue. Microscopic examination showed flattened cells without any signs of malignancy.
Surgical Intervention
The patient underwent a successful excisional surgery under local anesthesia. He was discharged with standard post-operative care, including pain medication and antibiotics. The patient recovered well without complications.
Intra-operative view of the left popliteal mass undergone complete excision.
What are Baker’s Cysts?
Baker’s cysts, fluid collections from the knee joint, often arise from conditions like osteoarthritis or meniscal tears. They are commonly diagnosed via ultrasound or MRI and are frequently asymptomatic, discovered incidentally during exams for other issues, according to the American Academy of Orthopaedic Surgeons.
Other Cyst Types
While ganglion cysts (usually in the hand and wrist) and meniscal cysts (associated with meniscal tears) can occur near the knee, epidermal inclusion cysts in this location are extremely rare. Annually, about 12.9 million Americans visit physicians for skin and soft tissue lesions, according to the CDC, highlighting the prevalence of skin issues.
How Trauma Can Cause Cysts
These cysts can form after trauma, where skin cells become trapped beneath the surface. While typically benign, they can cause discomfort if they become inflamed or infected. Complete surgical removal is usually curative.
Preoperative view of left popliteal swelling, round in shape, with no inflammatory signs.
Previous Cases
A review of existing literature indicates only a handful of similar cases, reinforcing the uniqueness of this presentation. Including this instance, only seven reported cases of epidermal cysts around the knee exist, with four in the popliteal fossa and three in the frontal knee area.
Conclusion
The case emphasizes the importance of considering rare conditions when common diagnoses don’t quite fit. Atypical presentations of masses require thorough investigation to ensure accurate diagnosis and appropriate treatment.
