Sixth month history of slowly enlarging mass in the left knee with pain.
A 57-year-old woman presented with sixth month history of slowly enlarging mass in the left knee with pain. There was no history of trauma. Physical examination revealed mild swelling over left suprapatellar area. A firm, fluctuating and slightly tender mass approximately measuring 4.5 x 3 x 2 cm was palpated superior to patella. Range of motion of the knee was not restricted. The left knee radiographs revealed somewhat triangular shaped opacity in the suprapatellar area. The computed tomographic (CT) scan shows corresponding fluid attenuation mass situated beneath quadriceps tendon. The magnetic resonance (MR) images demonstrated fluid intensity mass with enhancement of the surrounding thickened synovium, without any fluid in the medial and lateral compartments of knee, consistent with isolated suprapatellar bursitis. This was confirmed with arthroscopic examination which showed seperation of distended suprapatellar bursa from the knee joint by complete septum without any communications.
In early embryonic life, the knee joint is separated into three cavities partitioned by thin synovial membranes: suprapatellar, inferior medial, and inferior lateral compartments. Involution of the membrane leads to formation of a single joint space by approximately 12 weeks of embryonic life. Suprapatellar synovial plica is a remnant of the suprapatellar septum, which separates the suprapatellar cavity and the medial and lateral joint compartments. It varies in morphology and adult suprapatellar septum can be classified into 4 types: Type I is complete septum. In this type, the suprapatellar bursa and the knee joint are completely separated by the septum. The incidence of type I is 16% of adult knees. Type II is a perforated septum with one or more openings, called porta. Type III is residual septum with small residual fold and this type is most common (43%). Type IV is complete involution of septum. Patients with isolated suprapatellar bursa usually remain asymptomatic throughout life. Isolated suprapatellar bursitis has rarely been reported. Trout et al described five patients with abnormal suprapatellar plicae that led to joint compartmentalization and distention of bursa manifested as soft tissue mass. Yamamoto et al described CT and arthroscopic findings in a patient with isolated suprapatellar bursitis. Zeiss et al reported a patient with suprapatellar bursitis mimicking localized pigmented villonodular synovitis. Lee et al presented two cases of suprapatellar synovial cysts, one case with narrow communication with the knee joint and the other with no communication. Elmer reported a young patient with bilateral, isolated suprapatellar bursitis. El-Khoury et al and Katz et al reported unusual cases of pigmented villonodular synovitis occurring in an isolated, non-communicating suprapatellar bursa. Boya et al described a case of synovial osteochondromatosis in imperforated suprapatellar bursa. Most of these cases reported history of antecedent trauma to the knees. In our case there was no such history. Most cases of suprapatellar bursitis are excised surgically. Arthroscopic procedures are helpful if a central porta is present. In that case it may be opened arthroscopically, allowing free communication between suprapatellar bursa and the knee joint to reduce the pressure in inflamed bursa.
Isolated suprapatellar bursitis
Based on the provided X-ray, CT, and MRI images, a localized, roughly round or oval low-density/high-signal region is visible in the suprapatellar area (anterior) of the left knee joint's soft tissue. The margins of this lesion are well-defined, showing cystic characteristics with fluid signal inside, and no obvious soft tissue mass or bone destruction is observed. The adjacent bony cortex remains continuous, and no obvious wear or erosion of the articular surfaces is detected. On the T2-weighted MRI images, the lesion appears as a hyperintense area, consistent with a fluid collection in a synovial bursa or tendon sheath. Overall, these findings suggest a suprapatellar synovial cystic lesion that may or may not communicate with the joint.
Considering the patient is a 57-year-old female presenting with a slowly enlarging anterior left knee mass over six months, accompanied by pain, and imaging demonstrating a localized, fluid-filled cystic lesion without significant surrounding bone or joint damage, the most likely diagnosis is:
Isolated Suprapatellar Bursitis
If further clarification is needed, arthroscopic evaluation or fluid aspiration for laboratory analysis may be considered. Should there be any suspicion of synovial proliferation or other soft tissue pathologies, a biopsy could help rule out rarer conditions such as pigmented villonodular synovitis.
If the cyst is large or conservative treatment proves ineffective, arthroscopic surgery can be considered to explore, excise, or open up any narrowed “porta” (synovial channel) that might be present, allowing decompression of the bursa and reduction of inflammation.
This analysis report is based on the current imaging and clinical information provided. It is intended for reference in clinical decision-making and does not replace in-person examination and specialist consultation. If any doubts arise, please seek medical attention promptly and follow a healthcare professional’s guidance for further assessment or treatment.
Isolated suprapatellar bursitis
