Hoffa fat pad ganglion cysts are intra-articular ganglion cysts and are the most common mass-like lesions within the Hoffa fat pad.

Epidemiology

Hoffa fat pad ganglion cysts are rare and less common than cruciate ligament ganglion cysts ^1,2.

Clinical presentation

Ganglia within Hoffa’s fat pad can be asymptomatic or can cause pain and swelling or present as a palpable mass ^1,2.

Pathology

Ganglion cysts within Hoffa’s fat pad are usually well-defined, smooth-walled, uni- or multilocular, lobulated cystic masses surrounded by dense connective tissue and filled with viscous, mucinous material like other ganglion cysts. They lack a synovial membrane ^1-3.

Aetiology

Like with other ganglion cysts, the pathogenesis is controversial and comprises the following theories ^2-4:

• a sequel of mucoid degeneration

• cyst formation as a consequence of trauma or tissue irritation

• release of hyaluronic acid by mesenchymal stem cells and consecutive cyst formation

• synovial herniation

• congenital translocation of synovial cells

Location

Ganglion cysts of Hoffa’s fat pad are usually located anterior to the anterior horn of the lateral meniscus ¹.

Radiographic features

MRI

MRI is the best modality for the visualisation and evaluation of intra-articular ganglion cysts. The typical appearance is that of a well-defined lobular cystic mass within or adjacent to Hoffa’s fat pad ^1,2,4.

• T1: usually hypointense but will depend on protein content

• T2: hyperintense

• PDFS/T2FS: hyperintense

Treatment and prognosis

Management options depend vastly on clinical symptoms and include conservative measures, image-guided percutaneous aspiration as well as arthroscopic or surgical excision ^2,4-6.

Differential diagnosis

The differential is that of cyst-like lesions around the knee:

• anterior and/or posterior cruciate ganglion cyst

• meniscal cyst

• synovial cyst

• synovial sarcoma