CASE 134
By: Dr. Nizar Al-Nakshabandi MD, FRCPC
HISTORY: 25-year-old male with limitation of knee extension. On examination, a palpable mass is felt in Hoffa’s fat pad.
What are your findings?
What is the differential diagnosis?
What are the causes?
FINDINGS:
Sagittal T2-weighted image [A] demonstrates a large lobulated fluid signal focus within Hoffa’s fat pad centrally. Internal septations are present.
Axial proton density [B] with fat saturation demonstrates a well-demarcated intermediate to high signal intensity lesion in Hoffa’s fat pad.
DIFFERENTIAL DIAGNOSIS:
· Synovial myxoma.
· Meniscal or para meniscal cyst.
· Synovial cyst.
· PVNS.
· Hemangioma.
· Aneurysm.
· Synovial sarcoma.
· Ganglion cyst.
DIAGNOSIS:
Infrapatellar [Hoffa’s fat pad] ganglion cyst.
PEARLS AND DISCUSSION:
Ganglion cyst are a common finding with MRI (mostly around the wrist). However, they can also be seen in other parts of the body and can be confused with other benign and malignant processes.
At a pathological level, ganglia are fluid sacs containing mucinous material but no sign of lining. They could represent a synovitis herniation or a coalescence of small degenerative cysts.
At a histological level, no difference between intraosseous ganglia and extraosseous ganglia.
Clinical presentation: they are usually incidental findings with no clinical symptoms. However, large ganglia may compress on the neurovascular structures. They are present as a nonpainful smooth mass around the joint. The can be of variable size. In our case pain clicking and stiffness will be seen, sometimes a palpable mass in the knee can be detected. If the cyst is anterior to the ACL, they may limit the extension of the knee.
Pathogenesis of ganglia is uncertain. They may have developed from the outpouching of joint capsule because of soft tissue irritation or chronic damage leading to connective tissue degeneration. Since ganglia can collapse following rupture they can have the appearance of a solid mass.
Usually ganglia do not require treatment. If there is pain or mass effect or for any cosmetic reasons, they can be drained under ultrasound guidance or surgically removed. Recurrence ranges from 4% to 40%.
FURTHER READING:
1. el-Noueam KI, Schweitzer ME, Blasbalg R, et al. Is a subset of wrist ganglia the sequela of internal derangements of the wrist joint? MR imaging findings. Radiology 1999; 212:537-540.
2. Steiner E, Steinbach LS, Schnarkowski P, Tirman PF, Genant HK. Ganglia and cysts around joints. Radiol Clin North Am 1996; 34:395-425, xi-xii
3. Ghazal L, Chandrashekar S, Fersia O, Hirst P. MRI misinterpretation of a large infrapatellar fat pad ganglion of the knee: a case report and literature review. The Internet Journal of Radiology 2010; 13
