Intraarticular nodular fasciitis of the knee

A 47-year-old man presented in the orthopaedics department with right knee pain of 4 months duration, preferably in the posterior aspect of the joint. There was no history of trauma.

At the physical examination, the meniscus manoeuvres and pivot shift test were negative, and there were no palpable masses.

Conventional radiographs did not show any abnormality. Bone density and joint space were preserved.

The Magnetic Resonance Imaging (MRI) of the right knee showed a solid nodular lesion in the posterior intercondylar region, just posterior to the posterior cruciate ligament. The lesion presented well-defined margin with lobulated shape and measured 1,8 x 2 x 3,3 cm.

It was predominantly hyperintense compared to surrounding muscle on Proton Density (PD) weighted images, with and without fat suppression (FS) technique.

Minimal joint effusion was also shown.

The MRI was performed without intravenous contrast, because the patient refused to use it.

The diagnoses suggested by the radiologist after the MRI were focal synovitis and pigmented villonodular synovitis.

Due to the finding, the orthopaedic surgeons decided to undergo arthroscopic surgery to excise the lesion.

The postoperative radiological study was performed 6 months after the surgery, and it does not show any residual or new lesion.

Background

Nodular fasciitis is a self-limiting benign lesion characterized by a myofibroblastic proliferation in patients between 20 and 50 years old [2]. It usually appears as a palpable mass in the subcutaneous tissues and attached to the fascia [5].

Intraarticular nodular fasciitis is rarely reported and only 21 cases have been documented in the literature (3).

Clinical Perspective

Most of the patients with intraarticular nodular fasciitis presented with painful joint, limited range of motion, palpable masses, joint effusion or hemarthrosis. 15% of the patients had history of previous trauma before the diagnosis [2]. The duration of symptoms before surgical excision ranged from 1 month to 1 year [3]. Intra-articular nodular fasciitis tended to have a longer preoperative history than the usual variants [2].

The knee was the most common joint affected (70%) followed by the shoulder, the hand, the hip and the elbow [1].

Imaging Perspective

The conventional X-ray of the painful joint is usually normal. The MRI is the best imagine technique for characterize and detect intraarticular nodular fasciitis [3].

In the MRI the disease usually presents as a circumscribed lesion ranged from 1 to 6 cm [3]. The T1-weighted MRI shows iso-signal intensity compared to the surrounding muscle, while the T2-weighted MRI and the DP-weighted MRI showed high signal [3].

Contrary to subcutaneous nodular fasciitis, in the intraarticular form could show magnetic susceptibility artifacts in gradient echo sequences, as pigmented villonodular synovitis does [2].

Post-gadolinium-enhanced imaging demonstrated diffuse, slightly inhomogeneous T1-weighted enhancement of the nodular lesions [5].

Outcome

As intraarticular nodular fasciitis is rarely encountered, it is commonly misdiagnosed, and most cases are thought to be intraarticular diseases with higher incidence rate such us: pigmented villonodular synovitis, synovial chondromatosis, desmoid-type fibromatosis or giant cell tumour of tendon sheath [1].

Although intraarticular nodular fasciitis usually regress spontaneously and it does not recur in the follow up, almost all the patients reported in the literature underwent arthroscopic surgery to excise the lesion.

The diagnosis must be confirmed by the anatomopathological study, where the lesion shows typical histologic features of nodular fasciitis: unencapsulated and well-circumscribed lesions composed of uniform spindle cells in bundles with vesicular chromatin, small nucleoli, and eosinophilic cytoplasm, no significant cytologic atypia or pleomorphism.  Contrary to conventional variants of nodular fasciitis, it is common for the intraarticular form to find prominent stromal hyalinization, cystic degeneration and hemosiderin deposition, because of the repeated frictional trauma due to the anatomic localization [1].

After surgery, symptoms relieved in a few days [3].

Take Home Message / Teaching Points

Nodular fasciitis should be included in the differential diagnosis for any intraarticular mass lesions. Although MRI is useful to characterize the lesion, histological examination is essential to establish the diagnosis.