Teaching Case

A 58-year-old male patient presented with a palpable small nodule in the medial aspect of the plantar fascia, near the head of the first metatarsal bone.

A 58-year-old male patient presented with a palpable small nodule in the medial aspect of the plantar fascia, near the head of the first metatarsal bone, which was found to be exacerbated at the limit of dorsal flexion. The lesion was found to be bilateral but asymptomatic. The pain had been present for eight months, and there was no history of trauma. The MR imaging study was performed using an RM scanner (0, 2) with a dedicated coil. The images showed the presence of a round soft-tissue nodule involving the medial fibers of the central cord of the plantar fascia, below the level of the first metatarsal joint. The examination consisted of T1-weighted spin-echo (SE), PD-weighted turbo-spin-echo (TSE), T2*-weighted gradient-echo (GE) and GE-STIR sequences, which were performed in the axial, sagittal and coronal planes.

Plantar fibromatosis comprises a group of soft-tissue lesions that can mimic a malignant process in the soft tissues of the foot, and it may occur either as a superficial nodular mass (Plantar fibromatosis) or as a deep infiltrative mass (aggressive fibromatosis). It affects middle-aged people who have a genetic predisposition for other fibromatous conditions including palmar fibromatosis (Dupuytren’s contracture). Less frequent than its superficial counterpart, deep or aggressive fibromatosis may occur anywhere along the plantar fascia. Highly aggressive, it tends to infiltrate the adjacent musculature. This lesion, which tends to be multinodular or an aggregate of multiple nodules, is usually present in the medial aspect of the plantar fascia, near the first metatarsal midshaft, and the neck region. A bilateral lesion occurs in 10%–25% of the cases. This pathological process is histologically represented by a benign proliferation of well-differentiated fibroblasts and myofibroblasts within the plantar fascia. When they reach maturation, in the late phase, the nodules become hypocellular, the collagen is more abundant and dense, and fibroblasts gradually transform into fibrocytes. The symptoms are related to the location and size of the nodule; however, moderate pain and swelling can occur. A small nodule is often palpable if it is superficial. On the contrary, deeper lesions tend to be more insidious and may not be detected until they elicit a mass effect on the adjacent musculature or neurovascular structure. Surgical excision is recommended, using a wide margin, because the recurrence rate for a simple excision is particularly common in nodules with infiltration into the skin or deep tissues. In fact, if the aponeurosis has not been totally removed, the lesion may locally recur. The differential diagnosis includes several benign and malignant soft-tissue tumors, which can be classified into those arising from the plantar fascia (plantar fasciitis and chronic fascial rupture) and those arising from other nonfascial soft-tissue tumors of the foot (a ganglion, an inclusion cyst, foreign body granuloma, nerve sheath tumor, or synovial sarcoma). MR imaging is able to delineate the full extent of the disease process. Fibromatosis, depending on the tissue composition and cellularity of the lesion, may have a variety of appearances.On T1-weighted images, the lesions are seen to be either slightly hyperintense or isointense in comparison with the signal intensity of muscle. Dense clusters of collagen-like appear on areas of low signal intensity. On T2-weighted images, a wide spectrum of signal intensities has been observed. Compared to the signal intensity of muscle, the lesions may appear homogeneously low in signal intensity, isointense to slightly hyperintense, or heterogeneously bright. The higher signal intensity on T2-weighted images may be a sign of a more aggressive growth. The aggressive fibromatosis, therefore, demonstrates high signal intensity on T2-weighted images more often than the superficial fibromatosis. After the administration of the intravenous contrast, different kinds of equally variable enhancement patterns are seen to occur, from an absence of enhancement of the lesion to a marked heterogeneous enhancement.