An Abnormality Within The Suprapatellar Pouch Of A Cadaveric Donor: A Case Study

Introduction The suprapatellar pouch lies between the quadriceps tendon and the femur and contains synovial fluid from the knee. This structure, which communicates with one of the largest weight-bearing joints in the body, is prone to structural variation and pathology. Understanding and defining the various anatomical deviations and pathological conditions that arise within the suprapatellar pouch is critical in improving radiologic interpretation and in guiding treatment plans for patients with the all-too-common complaint of “knee pain.” Objective This report details an anatomic abnormality within the suprapatellar pouch of a cadaveric donor's left knee. The gross morphology and histologic features of this unusual finding are described in this abstract and are compared to the most likely differential diagnosis. Materials and Methods The decedent's medical history was obtained from the embalming report and death certificate. The dissection site was examined closely to evaluate the gross morphology of the lesion. The opposite knee was unavailable for evaluation due to its removal for a previous dissection. Tissue samples were collected and processed for hematoxylin and eosin staining. The slides were evaluated to obtain the histologic diagnosis. Results The decedent was a 79-year-old Caucasian female with a past medical history of unspecified lung cancer, hyperlipidemia, hypertension, and diabetes mellitus type 2. She had a recorded BMI of 43. She previously worked as a laborer in a textile factory. There was significant and diffuse edema noted in the embalming report, with no surgical or arthroscopic scars around the knee. Degenerative changes of the left femoral condyles were present. A fibrous web-like structure was observed within the left suprapatellar pouch that appeared to be in direct continuation with the synovial lining of the pouch. The diameter of each web-like strand ranged from 1.0 to 8.0 mm and the length of the structures varied from 0.5 to 7.0 cm. The histologic samples of the webbing demonstrated fibrous connective tissue with inflammatory cells and hypertrophied synovial lining. Additionally, infiltrative tissue was present within the posterior aspect of the pouch that was directly adherent to the web-like structure. The tissue within the suprapatellar pouch demonstrated villous projections of mature adipose with a distinct synovial lining surrounding it. Conclusions and Significance The macroscopic and histological findings of this lesion are most consistent with lipoma arborescence and intra-capsular fibrosis of the left suprapatellar pouch. This lesion is distinct from an intra-articular lipoma, which is characteristically a singular rounded mass and microscopically, has a thin fibrous layer without synovial lining. Although rare, an understanding of lipoma arborescence can help guide clinical decisions. Recognizing its features apart from that of lipoma is also crucial as the management between these two is different.