J Cutan Pathol 1996: 23: 437^44Ptinted in Denmark - all rights resewed

Copyright Mimksgaard 1996Journal of

Cutaneous PathologyISSN 0303-6987

Solitary cutaneous myofibromas in adults:report of six cases and discussion ofdifferential diagnosis

Six solitary, dermal or subcutaneous lesiotis occurring in adultpatients are presented. These masses had a circtunscribed, lobu-lated configurafion; they were composed of fusifortii and epi-thelioid cells that lacked atypical nuclear features. The patternof growth featured fascicles and nests, a myxofibrous stroma,and prominent blood vessels with a focally "heniangiopericy-toid" appearance. Itnmunohistochemical analyses showed utii-form reactivity for vimentin and alpha isoforni-actin, with nega-tivity for desmin and neural determinants. The overall appear-ance of the lesions was sitnilar to that of "infantile tiiyofibroma-tosis," and corresponded to previous descriptions of "solitarymyofibroina(tosis)" in adults. Immunophenotypic and ultra-structural support exists for a proposed myolibroblastic naturefor such proliferations. Differential diagnostic consideratiotis in-clude neurothekeomas, plexiform fibrous histiocytomas, nodu-lar fasciitis, cutaneous infiammatory psetidotumors, demiato-myofibromas, leiomyomas, atid other fortiis of fibromatosis af-fecting the skin and superficial soft tissues. -

GuitartJ, Ritter JH, Wick MR. Solitary cutaneous myofibromasin adults: report of six cases and discussion of differential diag-nosis. J Cutan Pathol 1996: 23: 437-444. Mtitiksgaard 1996.

Joan GuitartS Jon H. Ritter^ andMark R. Wick^'Section of Dermatopathology, Department ofDermatology, Northwestern University MedicalCenter, Chicago, iliinois, and the ^Division ofSurgicai Pathoiogy, Washington University MedicalCenter, St. Louis, Missouri, USA

Dr. Joan Guitart, Section of Dermatopathoiogy,Northwestern University Medical Center, Tarry 4-711, 303 East Chicago Ave., Chicago, iilinois60611,USA

Accepted March 27,1996 ' " ' " ' " ' ' ' ' '

A group of plexiform or lobtilated dermal mesen-chymal tumors has been recogtiized which hassimilar histological, immunohistochemical, andultrastructural features. It is incompletely charac-terized and may be interpreted differently by vari-ous dertnatopathologists (1, 2). Some reportedcases in this categoty have been described asnerve sheath myxonias, plexiform fibrohistiocytictumors, and intiadermal nodular fasciitis. Al-though these probably differ from one another ata basic level, they may be related to still other le-sions that are herein presented as examples of sol-itary myofibrotna of the skin (SMF) in adtilt pa-tients. Myofibroblastic differetitiation is thoughtto be the unifying attribute of all of these cutane-ous proliferations.

Material and methods

Electronic records were searched in the division ofanatotiiic pathology at Washington UniversityMedical Center and the section of dermatopathol-ogy at Northwestern University Medical Center, inorder to retrieve all available examples of solitarytiiyofibroma of the skin iti adults. All lesions as-signed that diagnosis - as well as "fibroma," "fibro-matosis," and "myofibromatosis" were reexatn-ined microscopically; those proliferations showinghistologic profiles that were compatible with thedesired category were retained for further sttidy,providing that they had ariseti in adult patients.Criteria used in the selection of cases inclttded apredominance of spindle cells; a lobular and/or

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Table 1. Antibodies employed in the analysis of solitary myofibroma of the skinin adults

Tabie 2. Clinicopathoiogic information on 6 cases of soiitary myofibroma ofthe skin in adults

Antibody Source Diiution Case Age/Sex Loc/Dur Size Therapy Outcome

Anti-vimentin, (V9)*

Anti-desmin, (D33) >' /

Anti-aipha-actin (1A4)

Anti-epitheiial, membrane antigen, (E29)HMB-45Anti-Si 00 protein**Anti-neuron, specific enoiase**

BioGenex Co.Dubiin, CADakoPatts Co.Carpinteria, CASigma ChemicaiCo. St. Louis, MCDakoPatts Co.DakoPatts Co.DakoPatts Co.DakoPatts Co.

1:600

1:10

Prediiuted

1:751:501:8001:300

*Aipha-numeric entries in parentheses represent cione designations ot mon-ocionai antibodies . ,** Polycional rabbit heteroantiserum

fascictilar growth pattern; focally or globally myx-oid stroma; a lack of marked nuclear atypia; andconjoint actin-positivity and desmin-negativity byimmunohistochemical analyses (3-8). Lesionswith the microscopic appearance of so-called "det-matomyofibroma" - as described by I^mino et al.(9) - were specifically excltided from consider-ation.

Immunohistochemical studies were performedon 5 micron paraffin sections of each formalin-fixed lesion, using the avidin-biotin-peroxidasecomplex method as described previously (10). Pri-mary antibodies included reagents directed at vi-mentin, desmin, alpha-isoform ("smooth muscle")actin, SlOO protein, HMB-45 antigen, neuron-spe-cific enoiase (NSE), and epithelial membrane an-tigen (EMA) (Table 1). Negative controls were ob-tained by substituting nonimmune murine ascites

1 67/F Rt. leg/"IVlonths"1.2cm Sub.exc. NER:18mo.2 73/M RL palm/2 mo. NR Excision NER:18mo.3 31/E RLarm/NR 0.6 cm Curettage NER:12mo.4 57/M RL buttock/1 yr. 1.0 cm Excision NER: 24 mo.5 34/M Rt. knee/2 yr. 1.3 om Excision NER: 21 mo.6 58/M Face/6 mo. 1.5 cm Excision NER: 8 mo.

Loc = Anatomic iocation; Dur = Duration of growth;Sub. exc. = Subtotal excision; NR = Not recorded;NER = No evidence of recurrence

fitiid for primary antibodies, and positive controlswere represented by sections of "stock" tissuesknown to contain the determinants of interest.

In 2 cases, sufficient tissue existed in paraffinblocks for retrieval of a portion thereof for ultra-structural studies. After deparaffinization and re-hydration, the specitnens were postfixed in glut-araldehyde and osmium tetroxide, embedded inepoxy resin, sectioned with a diamond knife,mounted on copper grids, and stained with uranylacetate and lead citrate. Resulting preparationswere examined with a Philips 400 electron micro-scope. . . . , . .

ResultsClinical dataClinical data on 6 available cases of adult SMF aresummarized in Table 2. Briefiy, the patientsranged in age from 34 to 73 years and included 4men and 2 women. They had lesions of the trunkor extremities in 5 instances; the remaining tumor

y '

Fig. 1. Low power overview ofsolitary myofibroma of the skin(SMF), showing well-demarcatedmass with sharp interfaces with thesurrounding dermis.

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Solitary cutaneous myofibromas in adults

arose in the facial skin. The stated dtiration ofgrowth was between 2 months and 2 years, andmaximal lesional dimensions varied from 0.6 cmto 1.5 cm. A history of trauma to the lesional areaswas not elicited in any case. The proliferationswere described clitiically as non-ulcerated, fittii,tan-pink, mobile, non-tender nodules. Subtotal ex-cision or curettage of the tumots was performedin 2 cases, whereas the others were removed com-pletely by surgical tneans. None of the patients de-veloped recurrences after follow-up periods of 8 to24 tiionths.

Histologic findingsAll examples of SMF showed acanthosis and focalspongiosis of the overlying epidermis, with atrophyand effacement of the rete ridges at the center ofthe specimens. There was also hyperkeratosis andparakeratosis with a serous exudate in the stratumcorneum in 3 cases. In the papillary dermis, cir-cumscribed and densely-apposed but ill-definedmicronodules and blunt fascicles of fusiform atidepithelioid cells were seen (Fig. 1), which were fo-caily connected to the walls of dilated and distort-ed intralesional blood vessels. Some of the latter as-sumed branched, "staghorn" shapes in each case(Fig. 2). Occasional mononuclear cells were tiotedimmediately around the vascular channels.

The lesions were cotnposed primarily of spindlecells with abutidant, partially-vactiolated cyto-plasm, and elongated fitsiform nuclei with dis-persed chromatin and iticonspicuous nucleoli(Fig. 3). The stroma within cellular fascicles wasmyxofibrous in nature, with foci of hyalinization.There was no nuclear atypia or necrosis, and mi-

totic figures were rare. Focally, dense collagenousbundles were tioted between the cellular lobules.Verhoeff-van Gieson staining done in 3 casesshowed clumped intralesional aggregates of elasticfibers in the upper dermis. Deposition of matricalacid tiiucopolysaccarides was demonstrated withthe Alcian blue stain at pH 2.0 in all cases. The le-sional cells were blue-red with the Massonttichrome stain, but cytoplasmic fibrillation couldnot be appreciated with this technique.

Results of adjuvant pathologic studiesAll lesiotis were uniformly reactive for vitnentinand alpha-isoform actin (AIA) (Fig. 4), whereasstains for desmiti, SlOO proteiti, HMB-45 antigen,NSE, and EMA were negative in each case. Thepattern of labeling for actin was particularly nota-ble, in that it showed a ring-like enhancement atthe cytoplasmic periphery of the positive cells.Electron microscopy on 2 lesions demonstratedthe presence of discontinuous pericellular basallamina (Fig. 5), and bundles of cytoplasmic thinfilatnents with focal interruption by dense bodies(Fig. 6). Rare pinocytodc vesicles were also notedbeneath the plastnalemtnae of the lesional cells.There were no visible intercellular junctions, andlong-spaced collageti was similarly absent in theextracellular space.

DiscussionThe 6 lesions described here were characterizedby a tiodular and lobttlar or fascictilar growth pat-tern, formed by a mixture of fusiform and polygo-nal cells with cytologic banality, myxofibrous stro-

Fig. 2. Complicated, branchedvascvilar structm'es within SMF,focally resembling those seenin hemangiopericytomas of softtissue.

' ^ , ^ ^ ^ "

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7%. 5. Fascicles of blandspindle cells are arranged inwhorls (A) in SMF. The cellscontain fusiform nuclei withdispersed chromatin,indistinct nucleoli, and nomitotic acti\'ity. Cytoplasm ismoderate in amount and non-fibrillar (B).

ma, rich irregularly branching vasculature, andimmunoreactivity for AIA. The nature of similarproliferations reported previously is such that theyhave been likened to myofibromatosis of the softtissues in children. Although some authors havesuggested a neural or fibrohistiocytic origin forsuch lesions, their immunohistological and ultra-structural attributes are instead most compatiblewith a myofibroblastic lineage.

Myofibroblasts - that is, elements with featuresof both fibroblasts and smooth muscle cells -wereinitially described by Majno as a consequence ofstudies of granulation tissue (11). They are proba-bly mesenchymal cells that are capable of produc-ing collagen types I and III, but myofibroblastsconcurrently share (with smooth muscle cells) the

capacity for expression of AIA (12, 13). In culture,they differ from fibroblasts by their larger size,slower growth, and more stellate configuration(12). Although some studies have failed to detectdesmin in the former of these two cell types, smallamounts of that protein have itideed been seen byothers in an in vitro setting as well as in pathologicmyofibroblastic proliferafions in situ (14). There-fore, the lack of desmin, in the face of AIA-immu-noreactivity, txtay be helpful but is not specific tothe diagnosis of myofibroblastic proliferations.Other cells expressing AIA, but not desmin, in-clude uterine decidual cells, pericytes, myoepithe-lial cells, and submesothelial cells (14, 15).

The myofibroblast has been implicated in thegenesis of a variety of skin lesions, including such

440

Solitary cutaneous myofibromas in adults

/""ng. 4. Diffuse ' "'immunoreactivity for alpha-isoform ("smooth muscle")actin in SMF.

Fig. 5. Discontinuous basal laminasurrounds proliferating spindlecells in this electron micrographofa solitary cutaneousmyofibroma.

unlikely candidates as Kaposi's sarcoma atid juve-nile xanthogranuloma (16, 17). Those cutaneouslesions that are currently felt to show possible orprobable myofibroblastic differentiation (9) arelisted iti Table 3.

Solitary or multiple deep dertnal-subctitaneousnodules that appear during the first several weeksof life reflect the usual presetitation of infentilemyofibroma(tosis) (18). Such lesiotis also may iti-volve the deep soft tissue, bones, and even viscera,occasionally resulting iti death. In contrast, myofi-bromas of the skin in adtilts are single, small, andsuperficial lesions that exhibit an innocuous bio-logical behavior (3-8). Only a single case has beetifoutid to recur after surgical excision (6). We

agree with Daimaru et al. and Herrera and col-leagues, in the contention that solitary iiiyofibt"o-blastic tumors in adults may not be as rare as com-monly thought (4, 7). There is no particular singlesite of anatomic predilection for such lesions, butmost do affect the trtmk or extremities. Interest-ingly, deep subcutaneous SMFs comtiionly havesharply demarcated borders, in contrast to themore infiltrative growth that typifies purely der-mal lesions of this type. As in our cases, the prolif-erations usually have a nodular and lobular or fas-cicular pattern which t-esembles that of leiomyo-mas of the skin (3). Nevertheless, as metitionedabove, the cells of SMF are rarely positive fordesmin, as would be expected in classical smooth

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Guitart et al.

Table 3. Cutaneous and subcutaneous tumors witb probable or possibie my-ofibrobiastic differentiation

Probable myofibrobiastic iesions

Eibrous hamartoma of infancy

Cutaneous infiammatory pseudotumor

infantiie myofibromatosis

Solitary myofibroma of adults

Dermatomyofibroma

Desmoid tumor (aggressive fibromatosis)Infantile digital fibroma(tosis)

Nodular fasciitis

Paimar/piantar fibromatosis

Plexiform fibrohistiocytic tumor

Possibie myofibrobiastic lesions

inflammatory pseudotumor of the skin

Hypertrophic scar/Keioid

"Caiiular" neurotbekeoma

Atypical fibroxanthoma

Juvenile xanthogranuioma

Dermatofibroma

muscle tumors. "Ring-like" deposits of actin in thecells of SMF represent another distinctive charac-teristic (7).

A prominently vascular stroma - with the prolif-eration of irregular branching vessels - is often ob-served in this lesion as well. These vascular chan-

nels may assume a "staghorn" or "moose antler"pattern, and the presence of immature polygonalcells surrounding the vessels heightens the poten-tial resemblance of some areas of SMF to the im-age of hemangiopericytoma (3, 8). Nevertheless,these pericytoid components - which are so typi-cal of infantile myofibromatosis (19) - may some-times be inconspicuous or even absent in adult le-sions (3, 7). Indeed, the variability of microscopicappearances that is potentially seen in SMF hasbeen noted by Kutzner et al. (8), who proposedthat four subtypes be recognized - "leiomyoma-like," "spindle-cell," "biphasic," and "hemangio-pericytoma-like." These pattettis were all repre-sented (at least focally) in the 6 cases we have re-ported here.

A pattern similar to that of SMF - with vascularproliferation, tnyxoid stroma, and fascicular spin-dle-cell growth - can sometimes be seen in orga-nizing granulation dssue and early keloid nodules.This likeness raises the possibility that selected"myofibromas" also may represent an abnormalreparative process, rather than a form of neopla-sia. Although our patients denied trauma to theareas of their lesions, the lack of rectirrence afteronly incomplete excision in 2 cases would also beconsistent with a reactive nature for at least someexamples of SMF. Along the same lines, vaguelysimilar lesions involving other organs have beenreported as "infiammatoiy pseudotumors" (IPTs)(20, 21). Except for a lack of dispersed infiamtna-tion as seen in pseudotumors, SMF also bearssome resemblance to the cutaneous IPTs that weredescribed by Hurt & Santa Cruz (22).

There are several other tumors of the skin atidsoft tissue that should be considered in the differ-

Fig. 6. Cytoplasmic thin filamentsand dense bodies are evident inthis electron micrograph of asolitary myofibroma of the skin. ,

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Solitary cutaneous myofibromas in adults

ential diagosis of SMF. Kamino and coworkers re-cently described a lesion termed "dermatomyofi-broma" (9). Clinically, it takes the form of aplaque that is found predominantly on the upperextremities and upper trunk in young females. Ac-tin also has been demonstrated immvmohistologi-cally in this proliferation (9). However, the histo-logic image of dermatomyofibroma is basicallythat of a plaque-like lesion instead of a nodule. Itshows a fascicular, intersecting or parallel arrange-ment of the constituent tumor cell groupings in-stead of the micionodtilar pattern seen in mostexamples of SMF, and the neoplastic cells of der-matomyofibroma differ from those in SMF by ex-hibiting serpiginous nuclear contours. In addi-tion, adnexal structures are typically engtilfed byderaiatomyofibroma but displaced by SMF.Hence, microscopic distinction between these twoproliferations is a relatively straightforward pro-cess.

Enzinger & Zhang (23) have reported anotherdermal and subcutaneous tumor that Hollowoodand colleagues (2) believe to be yet another myofi-broblastic lesion. This is the so-called "plexiformfibrohistiocytic tumor" (PFT). As implied by itsname, that neoplasm is composed of interweavingfascicles of spindle cells, and it also may demon-strate a myxoid stroma. It has immunophenotypicand ultrastructtiral features that are similar tothose of SMF (2). In contrast to the latter lesion,however, PFT is also characterized by the presenceof focally histiocytoid, polygonal cell aggregates, aswell as scattered osteoclast-like, CD68-reactive gi-ant cells (2, 2.^). Those fmdings adequately serveto distinguish PFT from SMF. Such diagnostic pre-cision is important, because plexiform fibrous his-tiocytomas tend to behave as "borderline" malig-nancies (23) in counterpoint to the biological in-dolence of SMF.

Desmoid tumors are fibromatoses which arecomposed of infiltrative myolibroblastic elements.They show primary involvement of the deep softtissue, including fascia, aponeuroses, and skeletalmuscles (24). The nature of desmoids is still de-bated; some observers favor the opinion that theyrepresent exuberant reactions to trauma or hor-monal stimuli, but the majority view is that the le-sions are "borderline" malignant neoplasms (24).The growth pattern of such proliferations is typi-fied by a disorganized proliferation of relativelybland spindle cells in a variably myxoid or denselycollagenized stroma; hemangiopericytoid bloodvessels are not expected in desmoid tumors.

Reports of intradermal nodular fasciitis (NF)add another consideration to the differential diag-nosis of SMF (25, 26). NF is a reactive myofibro-blastic proliferation, classically presenting with a

rapidly growing subcutaneous mass without a der-mal component. The highly celhilar mitotic andmyxoid character of the tumor has yielded the al-ternate designation of "pseudosarcomatous fascii-tis." In those rare cases that involve the coiium ex-clusively, NF lacks the fascicular pattern and vascu-lar stroma that are seen in SMF.

Still other plexiform or fascicular myxoid tu-mors of the skin have been reported in the past as"neurothekeomas" or "nerve sheath myxomas."The presence of myofibroblastic features in someof those lesions was first noted by Harkin & Reed(27). They show a composition of polygonal andftisifoim cells, a wide spectrum of cellular density,and a subdivision by densely fibrous trabeculae(1). A nerve sheath origin for such lesions is sug-gested by this light microscopic appearance, aswell as by immunoreactivity for SI 00 protein insome examples. Occasionally, EMA-positive cellsmay be seen surrounding cellular lobules of classi-cal neurothekeomas; this finding probably repre-sents a participation by perineurial cells (28). Ul-trastructural findings have further substantiated aneural origin for most of these lesions (29). Thenature of "cellular" neurothekeomas, however, isless clear. Besides having different architecturaland cytological attributes than those of classicalneurothekeoma, the former tumors have beenconsistently negative immunohistologically forneural determinants (1). It is pertinent to this par-ticular discussion that a subset of cellular neu-rothekeomas is positive for AlA (1). Furthermore,electron microscopic evaluation of the latter neo-plasms has demonstrated features that could beconsistent with myogenous or myofibroblastic dif-ferentiation (30, 31). An interesting suggestion byCalonje et al. is that some of these lesions could,in fact, represent epithelioid leiomyomas (30),based on a perceived resemblance to the micro-scopic appearance of pilar leiomyomas as well asthe above-cited adjuvant findings in selected cases.Although desmin was absent in all lesions studiedby Calonje and colleagues, 3 of 9 cases they report-ed did express AIA.

In conclusion, the cases reported herein havedistinct features that suggest a myofibroblastic lin-eage. Their true nature is not certain, but an ab-normal lepaiative process or a benign neoplasticproliferation represent the two principal consider-ations. Bearing in mind that several cutaneousmesenchymal lesions have at least a partial myofi-broblastic component, solitary myofibroma ofadults is nevertheless a distinctive lesion with char-acteristic morphologic and behavioral features.

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