Quadriceps fat pad oedema (QFPE) syndrome

Clinical History

A 63-year-old woman had been suffering from anterior left knee pain for months. Pain was more relevant when climbing stairs. Clinical examination showed only tenderness to palpation of the suprapatellar region. Meniscal and ligaments knee tests were normal.

Imaging Findings

The MRI shows enlargement and abnormal signal of the quadriceps fat pad (Fig.1) with hyperintensity in STIR images (Fig. 2), and slightly decreased signal in T1 weighted images in comparison with the subcutaneous fat (Fig. 3). A mass effect on the suprapatellar recess is noted by a posterior convexity of the fat pad (Fig. 4, 5). Dense and diffuse enhancement of the fat pad appears after gadolinium intravenous contrast administration (Fig. 6).

Discussion

A.
There are three fat pads in the anterior knee. Two of them are suprapatellar; the quadriceps (or suprapatellar) fat pad (QFP) is anterior and the prefemoral fat pad is posterior, located just behind the suprapatellar recess. The third one is infrapatellar: the Hoffa fat pad. The QFP is located between the suprapatellar recess and the distal quadriceps tendon. Its normal anteroposterior thickness measures 5-9 mm in men and 4-8 mm in women [1].

Widespread use of knee MR studies has brought to the discovery of abnormalities of these fat pads, like in Hoffa’s disease. QFP MR abnormalities have only recently been studied.

The prevalence of quadriceps fat pad oedema with mass effect (QFPE syndrome) is 4%-12% of MRI in a routine clinical practice [1, 2].
Histopathologically, vasculitis and inflammatory changes of the fat pad have been described in one patient [2].

A clear aetiology to the QFPE syndrome has not been yet established. Some authors suggest a chronic impingement of the QFP between the extensor apparatus of the knee and anterior surface of distal femur leading to oedema and fibrotic changes of the fat pad [2]. The abnormality is bilateral in some patients [1, 2]. Many similarities with Hoffa’s disease are also evocative of a similar pathologic process [1, 2].

B.
QFPE syndrom is associated with anterior knee pain [1, 2] and clinical signs of meniscal tears [2]. There is also a correlation between quadriceps fat pad thickness and anterior knee pain severity [1].

C.
The typical MR imaging findings of QFPE syndrom are a diffuse and high signal in STIR and T2 fat-suppressed images, decreased T1 signal of the quadriceps fat pad, gadolinium enhancement, along with mass effect on the suprapatellar recess seen by a convex posterior border [1, 2].

D.
Most patients with QFPE syndrom are treated conservatively with anti-inflammatory drugs and physical therapy. One patient had a resection of the fat pad, followed by a total regression of the pain [2].
One reported case received also an intraarticular corticosteroid injection [1] with mild improvement of his symptoms.

E.
QFPE syndrom is a «new» radiological and clinical entity that can be associated to anterior knee pain, possibly as part of an impingement syndrome, and may be similar to Hoffa’s disease. Further studies (especially prospective) are needed to better understand the clinical relevance of this abnormality and its physiopathology.

Differential Diagnosis List

Final Diagnosis

Quadriceps fat pad oedema syndrome

URL:	https://www.eurorad.org/case/9818
DOI:	10.1594/EURORAD/CASE.9818
ISSN:	1563-4086