Keywords
fibroma of tendon sheath - intra-articular fibroma - knee - patellar tendon
Introduction
Fibroma of the tendon sheath (FTS) is a reactive tumor lesion with origin in the synovial
membrane of the tendon sheath, benign and rare,[1] first described by Geschickter and Copeland[2] in 1949. It is defined as a slow-growing nodular neoplasm adjacent to the tendon
sheath, clinically manifested by a small joint mass or effusion that essentially affects
people between 20 and 50 years of age, especially men, and more commonly the joints
of the fingers and hand, being relatively rare in large joints.[3]
[4] In these, the knee is the most common location, but most commonly associated with
the cruciate ligament and posterior capsule, with only three cases described in the
literature of tendon sheath tumors emerging from the infrapatellar Hoffa sheath.[5] The authors present a case of a fibroma of the patellar tendon sheath at the intra-articular
level.
Case Report
A 39-year-old male physician attended the orthopedics consultation for anterior pain
in the left knee, mild and present mainly in the initial phase of symptoms, with an
associated soft-tissue mass with about 12 months of evolution and slow growth. He
denied any history of previous trauma or previous complaints in this knee. The arc
of motion of the knee joint was preserved, with extension up to 0° and flexion up
to 130°, with discomfort starting at 90° of flexion. There were no joint effusion
of the knee or apparent instabilities. The mass was located in the anterolateral region
of the knee, lateral to the patellar tendon, and it was soft, painless on palpation,
of hard-elastic consistency, with about 4 cm in its largest axis and 2 cm in width.
Analytically, there were no alterations, and, in the sonographic and radiological
study of the knee, no alterations were observed as well. A Magnetic resonance imaging
(MRI) scan showed a tissue mass attached to the Hoffa pouch in the anterolateral region
of the knee anterior to the lateral plate of the tibia and posterolateral to the patellar
tendon, with 3.9 cm x 1.9 cm of isointense signal to the muscle on either T1 and T2,
with hyperintensity foci and well-defined edges ([Fig. 1]). We raised the diagnostic hypothesis of giant cell tumor (GCT). We chose to perform
a marginal resection of the lesion by lateral parapatellar miniarthrotomy, verifying
that it was an intracapsular and intra-synovial lesion with a pedicle to the Hoffa
pouch, lateral to the anterior tuberosity of the tibia and posterolateral to the patellar
tendon. The pedicle was resected, and the lesion was completely excised, and we obtained
an oval and irregular fragment measuring 4 cm x 2 cm x 1.5 cm, with a white, bright
and lobulated section surface ([Fig. 2]). On the pathological study, we observed that the lesion corresponded mainly to
a fibro-hyaline stroma, in which collagen fibers are limited by elongated fibroblasts,
monotonous and without atypia, as well as by a neovascular component, occasionally
observing a surface coated by synovial epithelium ([Fig. 3]). Thus, the diagnosis of fibroma of the patellar tendon sheath of the knee was established.
With ten months of evolution, the patient denies pain or any associated functional
limitation, with no signs of local recurrence.
Fig. 1 Images of the relative isointensity in the sagittal plane on T2 (a), T1 (b) and axial plane on T2 (c).
Fig. 2 Intraoperative photographs: (a) location and clinical appearance; (b) pediculated lesion before complete excision; (c) macroscopic appearance and measurement of the largest axis, with approximately 4 cm
(d) Relatively homogeneous intralesional macroscopic aspect.
Fig. 3 Photomicrography: (a) proliferation of fibrohyaline stroma; (b) elongated and monotonous fibroblasts; (c) surface coated by synovial epithelium.
Discussion
Fibromas of the tendon sheath mainly involve the joints of the fingers, hand and wrist,
and 75% to 82% are found in these locations, most often corresponding to a small,
firm, painless and slow-growing nodule dependent on the tendon or its sheath, with
a peak incidence in the third and fourth decades of life, and 3 to 5 times more common
among men.[6] Although the knee is the most frequently-involved large joint, less than 40 cases
have been described, most of them originating from the posterior cruciate ligament
or posterior capsule, and, in large joints, the most commonly-described symptoms are
pain and palpable mass smaller than 7 cm, in this order of frequency.[5] The case herein presented has most of the clinical and epidemiological characteristics
described as more common, except for the location, with only three cases described
to date that were dependent on the patellar tendon, and 3, on infrapatellar fat.[5]
The imaging studies with x-ray or axial computed tomography in this type of lesion
are normal, and erosive bone changes or soft-tissue changes may rarely be observed
in larger lesions.[7] The FTS MRI findings are usually constant on T1, generally showing a well-defined
lesion of low signal or isointense to the muscle; however, the T2-weighted images
show a great variability of patterns, most commonly a low-intensity signal to the
muscle, and the following can also be observed: a high-intensity central zone in a
low-intensity matrix, high focal intensity signal, or high-intensity image across
the mass.[5] The case herein described, when demonstrating an isointense lesion to the muscle
on T1 and relatively isointense also on T2, with hyperintensity foci, led the authors
to initially consider it to be a GCT, which is characteristically isointense or with
low intensity, either on T1 or T2.[8] In addition to GCT, whose presence in the histological examination of multinucleated
giant cells and hemosiderin deposits is fundamental for the diagnosis, FTS has as
a differential diagnosis nodular fasciitis.[5] The possible variability on T2 on the MRI makes the differential diagnosis of nodular
fasciitis uncertain; however, the fact that it rarely presents an intra-articular
location, being associated with a rapidly-growing and more commonly painful mass and
presenting older tissue, with more prominent myxoid stroma, with red-cell extravasation
and without any vascular pattern on the histological examination differentiate nodular
fasciitis from FTS, in which a nodular pattern, sometimes with small slit-like vascular
canals and coated with synovial epithelium, is typical.[4] The treatment of choice for these lesions is marginal excision, most often through
an open approach.[5] Although Chung and Enzinger[9] reported a recurrence rate of 24%, in large joints, such as the knee, there are
no cases described in the literature.[5] It should be noted, however, that given the absence of absolute certainty of complete
removal of the lesion in the case herein described, attention is important to exclude
recurrence.
In conclusion, this case herein reported reinforces the importance of including FTS
in the differential diagnosis of soft-tissue masses at the level of the knee.
