Pseudosarcomatous Fibroblastic Proliferations



Pseudosarcomatous Fibroblastic Proliferations


Elizabeth A. Montgomery, MD





Key Facts


Terminology



  • Nodular fasciitis: Rapidly growing myofibroblastic proliferation that is often cellular and mitotically active, but behaves in a benign fashion


  • Intravascular fasciitis: Rare variant of nodular fasciitis arising in association with small- and medium-sized vessels


  • Cranial fasciitis: Variant of nodular fasciitis involving soft tissues of scalp and underlying skull in infants


  • Proliferative fasciitis/myositis: Subcutaneous (fasciitis) or intramuscular (myositis) proliferation of ganglion-like cells in a background of myofibroblasts similar to those seen in nodular fasciitis


  • Ischemic fasciitis: Proliferation composed of zones of fat and fibrinoid necrosis with ingrowth of capillaries, fibroblasts, and myofibroblasts


Clinical Issues



  • Excellent prognosis: All these lesions are benign and typically do not recur even after incomplete excision


  • Recurrence should prompt re-review of prior sample to ensure initial diagnosis was correct


Microscopic Pathology



  • Myofibroblastic differentiation results in expression of “smooth muscle” immunohistochemical markers


Top Differential Diagnoses



  • Fibrous histiocytoma (dermatofibroma)


  • Neurofibroma


  • Fibromatosis


  • Malignant fibrous histiocytoma (undifferentiated pleomorphic sarcoma)


  • Leiomyosarcoma







This classic image of nodular fasciitis shows a myofibroblastic lesion with a storiform pattern, cystic spaces, scattered lymphocytes image, and extravasated erythrocytes.






Proliferative fasciitis features the same background myofibroblastic cells as nodular fasciitis image, with the addition of ganglion cell-like fibroblasts image. The latter are not true ganglion cells.


TERMINOLOGY


Abbreviations



  • Nodular fasciitis (NF)


Synonyms



  • Pseudosarcomatous fasciitis (nodular fasciitis)


  • Subcutaneous pseudosarcomatous fibromatosis (nodular fasciitis)


  • Atypical decubital fibroplasia (ischemic fasciitis)


Definitions



  • Nodular fasciitis: Rapidly growing myofibroblastic mass-forming proliferation that is often cellular and mitotically active, but behaves in a benign fashion


  • Intravascular fasciitis: Rare variant of nodular fasciitis arising in association with small- and medium-sized vessels


  • Cranial fasciitis: Variant of nodular fasciitis involving soft tissues of scalp and underlying skull in infants


  • Proliferative fasciitis/myositis: Tumefactive subcutaneous (fasciitis) or intramuscular (myositis) proliferation featuring ganglion-like fibroblasts in a background of myofibroblasts similar to those seen in nodular fasciitis


  • Ischemic fasciitis: Pseudosarcomatous proliferation composed of zones of fat and fibrinoid necrosis with zonal ingrowth of capillaries, fibroblasts, and myofibroblasts



    • Initially described as tumefactive pressure sore arising over bony prominences in debilitated patients, but some examples do not fit this profile


CLINICAL ISSUES


Epidemiology



  • Incidence



    • All are uncommon; nodular fasciitis is most common among them


  • Age



    • Nodular fasciitis: Most patients are in their 3rd and 4th decades


    • Intravascular fasciitis: Most patients are in their 3rd and 4th decades


    • Cranial fasciitis: Infants in peripartum period


    • Proliferative fasciitis: Middle-aged and older adults; rare in children


    • Ischemic fasciitis: Elderly patients


  • Gender



    • No predilection


Site



  • Nodular fasciitis: Classic site is forearm


  • Intravascular fasciitis: Classic sites are distal extremities (especially fingers) and head and neck


  • Cranial fasciitis: Head


  • Proliferative fasciitis: Classic site is forearm


  • Ischemic fasciitis: Classic sites are overlying sacral promontory or greater trochanter


Presentation



  • All of these pseudosarcomatous processes present as mass lesions, usually painless



    • Most lesions: 1-3 cm


    • Ischemic fasciitis lesions can be large


Treatment



  • Simple excision is curative


Prognosis



  • Excellent; all of these lesions are benign and typically do not recur


  • Recurrence should prompt review of prior sample to ensure that initial diagnosis was correct



IMAGE FINDINGS


General Features



  • Imaging generally shows well-marginated subcutaneous process



    • Exception: Proliferative fasciitis tracks along connective tissue septa


MACROSCOPIC FEATURES


General Features



  • Well-marginated but unencapsulated lesions


  • White to gelatinous cross section


  • Ischemic fasciitis can feature areas of hemorrhage


Size



  • Most 2-3 cm (exception is ischemic fasciitis, which can attain large sizes)


MICROSCOPIC PATHOLOGY


Histologic Features



  • Nodular fasciitis



    • Loose storiform pattern with tissue culture appearance, variable myxoid stroma, cystic spaces, strands of keloid-like collagen


    • Osteoclast-like giant cells common (see in most lesions if sought; can be enhanced by CD68 staining)


    • Scattered lymphocytes but negligible plasma cells


    • Extravasated erythrocytes unassociated with hemosiderin deposition


    • 3 reported forms: Myxoid, cellular, fibrous



      • Loose correlation with duration of lesions


      • Myxoid lesions often have been resected within 10 days of coming to clinical attention


      • Cellular and fibrous forms more longstanding


      • Some lesions show mixed patterns


    • Myofibroblastic differentiation results in expression of “smooth muscle” immunohistochemical markers



      • Lesions can thus be mistaken for leiomyosarcoma when mitotically active


  • Intravascular fasciitis



    • Similar features to nodular fasciitis, except has intravascular component



      • Often associated extravascular component encountered


    • Abundant osteoclast-like giant cells


    • Prominent mitotic activity can result in an incorrect diagnosis of intravascular leiomyosarcoma


  • Cranial fasciitis



    • Lesion of infancy sometimes attributed to birth trauma


    • Similar morphology to that of nodular fasciitis, but more myxoid


    • Some reported lesions are probably instead fibromatoses


  • Proliferative fasciitis



    • Predominantly plump stellate to spindled fibroblasts and myofibroblasts


    • Extravasated erythrocytes


    • Background myofibroblasts


    • Large ganglion-like fibroblasts



      • Macronucleoli, abundant amphophilic cytoplasm


      • Not true ganglion cells; no Nissl substance


    • Pediatric examples



      • Ganglion-like cells predominate


      • Exuberant mitotic activity


      • Mistaken for rhabdomyosarcomas in the past


      • Lack skeletal muscle markers (MYOD1, myogenin)


  • Ischemic fasciitis



    • Ill-defined focally myxoid masses


    • Lobular configuration


    • Most centered in deep subcutis


    • A few extend into skeletal muscle or tendon/aponeurosis


    • Overlying skin typically intact


    • Zones of fibrinoid necrosis and myxoid stroma


    • Necrotic zones rimmed by ingrowing ectatic thin-walled vessels



    • Atypical enlarged degenerating fibroblasts with abundant basophilic cytoplasm, large hyperchromatic nuclei, prominent nucleoli


    • Occasional mitoses, including atypical forms


DIFFERENTIAL DIAGNOSIS


Fibrous Histiocytoma (Dermatofibroma)



  • Mostly in differential diagnosis of nodular fasciitis


  • Typically small superficial lesions


  • Storiform pattern


  • Collagen trapping


  • Abundant background changes (foamy histiocytes, hemosiderin, plasma cells)


  • Overlying dermal hyperplasia


  • Factor VIII reactive; variable actin expression


  • Tend to recur locally when incompletely excised


Neurofibroma



  • Small superficial lesions


  • Serpentine nuclei


  • Shredded-appearing collagen, nuclei “plastered” against collagen fibrils


  • Myxoid change, mast cells


  • S100 protein(+), variable CD34(+)


  • Benign behavior


Fibromatosis



  • Large, deep, infiltrative lesions


  • Shoulder girdle, abdomen (in women in childbearing years), head and neck


  • Sweeping fascicles of myofibroblasts


  • Uniform collagen deposition


  • Prominent vascular pattern


  • Highly infiltrative


  • Express actin (myofibroblastic), show nuclear β-catenin labeling


  • Prone to local recurrences


Kaposi Sarcoma



  • Immunocompromised patients and elderly patients


  • In setting of AIDS/HIV, often in skin and mucosal surfaces of upper half of body


  • In elderly, in distal lower extremity


  • All examples associated with HHV8


  • Hyperchromatic spindle cells


  • Extravasated erythrocytes, hemosiderin, plasma cells, hyaline globules


  • Immunoreactivity: CD34, CD31, HHV8


  • Most behave indolently


  • Quasineoplastic: Can regress if immunosuppression is reduced


Malignant Fibrous Histiocytoma (Undifferentiated Pleomorphic Sarcoma)



  • Deep lesions in 6th, 7th decade


  • Storiform pattern


  • Pleomorphic nuclei


  • Outcome related to stage; overall 5-year survival about 60%


Embryonal Rhabdomyosarcoma



  • Mostly in differential diagnosis of proliferative fasciitis in children


  • Genital region/head and neck of young children


  • Enhanced cellularity beneath mucous membranes (cambium layer)


  • Atypical nuclei often without prominent nucleoli


  • Expresses skeletal muscle markers on immunolabeling


  • Responds to chemotherapy (70-80% 5-year survival)


Well-Differentiated Liposarcoma



  • Mostly in differential diagnosis for ischemic fasciitis


  • Large, deep lesions of proximal extremities and retroperitoneum


  • Mature-appearing adipose tissue lesion with relatively homogeneous low-power appearance


  • Lobules of fat separated by fibrous bands containing enlarged hyperchromatic nuclei


  • Occasional lipoblasts (not required for diagnosis)


  • Minimal mitotic activity


  • Low-grade sarcoma


Leiomyosarcoma



  • Wide range of clinical presentations


  • Perpendicularly oriented fascicles


  • Brightly eosinophilic cytoplasm


  • Hyperchromatic nuclei with blunt ends


  • Paranuclear vacuoles


  • Immunolabeling: Actin, desmin, calponin, and caldesmon all reactive


  • Outcome relates to stage and site


Pleomorphic Rhabdomyosarcoma

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Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Pseudosarcomatous Fibroblastic Proliferations

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