Age / Sex : 62 / M

Plantar fibromatosis

Discussion

Findings:

The mass of left sole is isointense to slightly hypointense relative skeletal muscle on axial T1WI (Fig.1), and heterogeneously hyperintense to skeletal muscle on axial T2WI (Fig.2). This mass is strongly enhanced on gadolinium enhanced T1WI (Fig.3). Sagittal MRIs of right foot show a nodular lesion involving plantar fascia, which have lower signal intensities on T1WI (Fig.4) and T2WI (Fig.5). The proximal and distal ends of the mass smoothly blends with the fascia, which is typical finding.

Differential Diagnosis:

Xanthoma

Epidermal cysts

Synovial sarcoma

Diagnosis: 

Plantar fibromatosis, bilateral
 

Discussion:

Plantar fibromasosis is infiltrative fibroblastic lesions most commonly found arising from plantar fascia or aponeurosis. Palmar and plantar fibromatosis belong to superficial fibromatosis. Medial location is most common and 20-50% of cases are bilateral.

MRI and US are used for the diagnosis. Typical imaging finding is lentiform lesion that blends with plantar aponeurosis at proximal and distal ends, which is best seen on sagittal MRI and longitudinal US.

The signal intensity of the mass is isointense to skeletal muscle on T1WI, slight hyperintense relative to skeletal muscle on T2WI, and significantly enhanced after gadolinium enhancement. Mature lesions are more likely to have low signal intensity on T2WI and less enhanced, which are less likely to recur locally after resection of the mass. Mature lesions are hypocellular and contains dense collagen. It can invade muscles or neurovascular bundles.

On US, small mass tends to be hypoechoic, otherwise the mass may show mixed echogenicity.
 

References:

1. Kransdorf MJ et al: Benign fibrous and fibrohistiocytic tumors. In Kransdorf MJ el al.: Imaging of soft tissue tumors. 2nd ed. Piladelphia: Lippincott William & Wilkins. 217-223, 2016 

2. Catherine C. Robert: Fibroblastic and myoblastic tumors. In Manaster BJ et al.: Diagnostic Imaging Musculoskeletal: Non-traumatic disease. Canada: Amirsys. 3:72-73, 2010