Plexiform fibrohistiocytic tumors (PFHT) are dermal or subcutaneous soft tissue neoplasms of uncertain behavior with biphasic tumor morphology and a plexiform growth pattern.
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Epidemiology
Plexiform fibrohistiocytic tumors are rare tumors. They can occur over a wide age range but are usually seen in adolescents and young adults 1-3. There is no gender predilection 1.
Clinical presentation
Most frequently plexiform fibrohistiocytic tumors present as slowly-growing ill-defined nodules or plaques 1.
Pathology
Plexiform fibrohistiocytic tumors are biphasic tumors with a plexiform matrix consisting of epithelioid histiocytoid and myofibroblastic spindle cells 1,2.
Etiology
The etiology of plexiform fibrohistiocytic tumors is unknown 1.
Location
Plexiform fibrohistiocytic tumors are tumors of the skin and subcutaneous tissues. They are most frequently found in the upper and less commonly the lower extremities. Other sites that are less frequently involved are the trunk and the head and neck region 1-4.
Macroscopic appearance
Macroscopically plexiform fibrohistiocytic tumors are usually small (<3 cm) undefinable lesions of firm consistency found in the lower portion of the dermis near the junction between the dermis and subcutis 1-3.
Microscopic appearance
The histological appearance of plexiform fibrohistiocytic tumors includes the following 1-3:
- infiltrative growth pattern with a plexiform or multinodular layout
- small nodules of epithelioid histiocytoid cells and multinucleated osteoclast-like giant cells with surrounding fibroblast-like spindle cells
- possible invasion of the skeletal muscle
- possible hemorrhage or chronic inflammatory infiltrates
- rarely hyalinized or myxoid stromal alterations or metaplastic bone formation
Immunophenotype
Fibroblastic cells express reactivity for smooth muscle actin and vimentin on immunohistochemistry stains 1. Histiocytoid cells and giant cells show positivity for CD68 3,5.
Radiographic features
On imaging plexiform fibrohistiocytic tumors are described as poorly demarcated infiltrative masses sometimes with contact or abutment of the underlying connective tissues like tendons, muscles and bone 4:
Ultrasound
On ultrasound, plexiform fibrohistiocytic tumors have been reported as hypoechoic nodules or discrete masses with some vascularity on color Doppler 4.
MRI
Plexiform fibrohistiocytic tumors are described as poorly demarcated infiltrative masses 4:
Signal characteristics
- T1: isointense to hyperintense signal
- T2: high intensity
- T2FS/STIR: hyperintense
- T1 C+ (Gd): avid enhancement
Radiology report
The radiological report should include a description of the following features:
- form, location and size
- tumor margins
- relation to the muscular fascia
- relation to adjacent bones and tendons
- relationship to local nerves and vessels
Treatment and prognosis
Treatment usually consists of surgical excision. Local recurrence is common, seen in 12.5 to 37.5% of cases 1-3. Rarely there are lymph node metastases and very occasionally distant metastases e.g. to the lung do occur 1-4.
History and etymology
Plexiform fibrohistiocytic tumors were first described in the literature in 1988 by the Austrian-American pathologist Franz Michael Enzinger and the Chinese pathologist Renyuan Zhang 2-4.
Differential diagnosis
The differential diagnosis of plexiform fibrohistiocytic tumors are the following 2-4:
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