Extraskeletal mesenchymal chondrosarcoma

Lorraine G. Shapeero, MD #{149}Daniel Vanel, MD #{149}Dominique Couanet, MDGenevieve Contesso, MD #{149}Lauren V. Ackerman, MD

Extraskeletal MesenchymalChondrosarcoma’

1 From the Departments of Radiology (L.G.S., DV., D.C.) and Pathology (G.C.), Institut Gustave-Roussy, Villejuif, France; Department of Radiology, Box 0628, University of California, San Fran-cisco, Medical Center, San Francisco, CA 94143 (L.G.S.); and Department of Pathology, State Univer-sity of New York at Stony Brook, Stony Brook (L.V.A.). From the 1991 RSNA scientific assembly.Received March 5, 1992; revision requested April 2; revision received September 9; accepted Septem-ber 14. Address reprint requests to L.G.S.

C RSNA, 1993

819

Among seven patients with extra-skeletal mesenchymal chondrosar-coma (EMC), three children (aged 3-6years) developed EMC in a centrallocation and four adults (aged 38-54years) developed EMC in both cen-tral and peripheral sites. Conven-

tional radiography and tomographyand computed tomography (CT) de-picted EMC as a soft-tissue mass with

ring, arc, stippled, and highly opaquecalci.fications in four patients. Con-trast-enhanced CT showed lobulationand peripheral tumoral enhance-ment, sometimes with central low-attenuation areas. On magnetic reso-nance (MR) images, EMC was alobulated mass with high signal in-tensity on T2-weighted images andenhancement with low-signal-inten-

sity focal areas on contrast-enhancedTi-weighted images. All adults de-veloped recurrences and/or metasta-ses and died. Of the three children,two were living and free of disease atthe end of the study and the thirdchild died of chemotherapeutic-in-

duced leukemia. Although imagingfeatures of EMC are nonspecific, itschondroid-type calcifications and fociof low signal intensity within en-hancing lobules may reflect its dualhistopathologic morphologic charac-teristics of differentiated cartilage

islands interspersed within vascularundifferentiated mesenchyme.

Index terms: Sarcoma, 10.369, 20.374, 40.375Soft tissues, calcifications, 40.375, 40.817 #{149}Soft

tissues, MR. 10.1214, 20.1214, 40.1214 #{149}Soft tis-

sues, neoplasms, 10.369, 20.374, 40.375

Radiology 1993; 186:819-826

M ESENCHYMAL chondrosarcoma,

first reported as a distinct en-tity by Lichtenstein and Bernstein ini959 (1), has been described as an un-common, aggressive variant of chon-drosarcoma with a strong tendencyto metastasize to distant sites (2). Incontrast to “conventional” or “com-mon-type” chondrosarcoma in whichsoft-tissue origin is rare, mesenchymalchondrosarcoma arises in an extra-skeletal location in 49% of reportedpatients (2-18), yet few authors (5,11-17) have discussed the imaging char-

acteristics of its extraskeletal formexcept for the plain radiographic find-ings (3,4,6-8,10). This study was un-dertaken to evaluate the imaging and

histopathologic findings and the clini-

cal course in patients with extraskele-tal mesenchymal chondrosarcoma(EMC).

MATERIALS AND METHODS

Of 224 chondrosarcomas (both skeletaland extraskeletal) diagnosed and treatedat our hospital between 1975 and 1991,eight were diagnosed as EMC. One man,who had a noncalcified soft-tissue extrem-ity mass on radiographs and no other im-aging studies, was excluded from the databecause clinical follow-up was not avail-able. Only patients with histopathologicconfirmation and without primary boneinvolvement were included in the study.

Two separate age groups of EMC wereidentified: the small child (two boys andone girl aged 3-6 years) and the adult(three women and one man aged 38-54years). Presenting symptoms varied withthe specific region of involvement. Twochildren with chest masses had acute res-piratory failure and mild cough, respec-tively; the third child had a palpable neckmass. Three adults sought medical consul-

tation because of an extremity mass withor without local pain or sciatica (Table 1).In the fourth adult, a mass was an inciden-tal finding on chest radiographs. The du-ration of symptoms prior to admissionvaried from days (the child with acute res-piratory distress) to 3 years.

Initial imaging studies were performedprior to needle biopsy and chemotherapy.Six of seven patients (three adults andthree children) received three to fivecourses of preoperative chemotherapyand then underwent reevaluation withmagnetic resonance (MR) imaging and/orcomputed tomography (CT) prior to sur-gery. All patients underwent surgical exci-sion, which confirmed the diagnosis ofEMC, followed by postoperative chemo-therapy (Table 1).

Length of patient follow-up was vari-able. Patients were studied from the timeof admission to the time of death or to thetime of termination of this study, which-ever occurred first (Table 1).

The adults were followed up 11-52months after the initial diagnosis (Table 1).Three adults developed recurrences (1-36months after surgery) and underwent re-peated excision and postoperative chemo-therapy. All adults developed pulmonarymetastases 7-48 months after surgery. Inaddition, in one adult, EMC metastasizedto multiple soft-tissue sites distant to the

primary site and to the epidural space,producing acute paraplegia that necessi-tated emergency myelography, laminec-tomy, spinal cord decompression, andpostoperative local radiation therapy. Alladults died.

Two children who were still living with-out disease at the end of this study werefollowed up for 6 and 10 years, respec-

tively. The third child, who had no evi-dence of recurrent or metastatic EMC, suc-cumbed to chemotherapeutic-induced

leukemia 6 years after presentation.All patients underwent conventional

radiography of their initial mass with soft-tissue and bone technique, and one un-derwent conventional tomography. CT

was performed in six patients with anExcel 2400 unit (Elscint, Haifa, Israel) at

Abbreviation: EMC = extraskeletal mesenchy-mal chondrosarcoma.

820 #{149}Radiology March 1993

Table 1

Clinical Data about Seven Patients with EMC

Patient No.1Age (y)/Sex Presenting Symptoms Location Initial Treatment Postoperative Treatment and Outcome

Children1/3/M* Anorexia, cough Lung Chemotherapy, excision Chemotherapy; well 6 years after surgery2/3/M* Acute respiratory

distressLung, with ex-

tension to pleuraChemotherapy, excision Chemotherapy; no recurrence nor metas-

tases from EMC; death 6 years after sur-gery from chemotherapy-induced leuke-mia

3/6/F Painless, palpablemass

Neck, with ex-tension to uppermediastinum

Chemotherapy, excision Chemotherapy and local radiation therapyof neck, upper mediastinum; well 10years after surgery

Adults

1/38/F Painful mass Buttocks andthigh

Chemotherapy, excision Chemotherapy; recurrences; pulmonarymetastases; death 12 months after sur-

2/43/F Sciatica, palpable

massThigh Chemotherapy, excision

gery

Chemotherapy; recurrences; pulmonarymetastases; death 11 months after sur-

3/44/M Painless, palpablemass

Calf Excisiongery

Chemotherapy; pulmonary, soft-tissue,epidural metastases; laminectomy fol-lowed by radiation therapy to epiduralmetastases; death 52 months after sur-gery

4/54/F Asymptomatic mass onchest radiograph

Chest wall ex-tending to lung

Chemotherapy, excision Chemotherapy; recurrence; pulmonarymetastases; death 36 months after sur-gery

* Also included in reference 15.

10-mm contiguous intervals without andwith an intravenous bolus of triiodinated(Telebrix; Guerbet, Aulnay-Sous-Bois,France) or hexaiodinated (Hexabrix; Guer-bet) contrast media (2 mL/kg in childrenand I mL/kg in adults, as permitted at ourinstitute). Angiograms of two tumors wereobtained (a thoracic mass and a thighmass). Non-contrast-enhanced MR imag-

ing (four patients) was performed with a1.5-T unit (Signa; GE Medical Systems,Milwaukee, Wis) with a spin-echo, mul-tiecho, multiplane imaging technique.Short Ti-weighted sequences (600/20

[repetition time msec/echo time msec])and long T2-weighted sequences (2,000/40, 80) were used for both peripheral andcentral masses. In addition to routine non-contrast-enhanced MR sequences, twopatients underwent contrast-enhancedTi-weighted MR imaging (600/20) after

intravenous administration of a bolus ofgadopentetate dimeglumine (diethylene-triaminepentaacetic acid; Magnevist, Ber-lex Laboratories, Wayne, NJ) (dose, 0.1mmol/kg). Follow-up CT and MR imagingwere performed with the same tech-niques.

Imaging studies were evaluated for thefollowing: (a) calcifications, (b) configura-tion of the tumor, (c) enhancement (at CT,MR imaging) or abnormal vascularity (atangiography), and (d) location and extentof the primary mass, recurrences, andmetastases. EMC was defined as a massthat was confined to the soft tissues and

caused no bone destruction or only super-ficial bone erosion. Imaging studies were

reviewed without benefit of the specificclinical or histopathologic data of the par-ticular patient.

The histopathologic slides from biopsy

specimens obtained prior to chemother-apy and radiation therapy and from surgi-cal specimens were reviewed. In this retro-spective study, however, the specific sitesof the pretherapy biopsies and the grosspathologic specimens were not availablefor exact correlation in the same plane asCT and MR imaging.

Imaging, histopathologic, and clinicaldata were compared within and betweeneach age group (adult and child).

RESULTS

All imaging modalities (convention-al radiography and tomography, CT,MR imaging, and angiography) de-picted EMC as large masses more

than 8 cm in length (8-20 cm), except

for a 5-cm mass in a 6-year-old girl.The masses did not erode or invadeadjacent bone. In the children, EMCwas found only in a central locationeither in the lung, with or withoutextension to the pleural cavity, or inthe lower cervical region extendinginto the mediastinum. In the adults,however, EMC occurred in both cen-tral (chest wall extending into thelung, buttocks extending to the thigh)and peripheral (thigh, calf) sites (Ta-ble 1). Four of the seven EMCs dis-played calcifications at conventionalradiography and tomography (Fig la,lb) and CT at presentation (Table 2).Although all these examinationsshowed the specific type of calcifica-tions (ring, arc, stippled, and highly

opaque), CT showed the extent of

these calcifications more clearly thandid correlative conventional studies.

At MR imaging, calcifications ap-peared as signal voids.

At contrast-enhanced CT and non-enhanced and enhanced MR imaging,both primary and recurrent EMC ap-peared lobular in configuration (Figs2-4, Table 2). MR imaging, however,more clearly defined the lobulation

than did CT (Fig 2a-2c). The signalintensity of EMC varied from isoin-tense with muscle on nonenhancedTi-weighted images to homoge-neously or inhomogeneously hyper-intense with muscle on proton-den-sity weighted and T2-weightedimages (Figs 2a, 2b, 4a, 4b). In compar-

ison with the appearance on nonen-hanced images, EMC was enhanced,except for small, focal, centrally lo-cated areas of low signal intensity (Fig4c), after gadopentetate dimeglumineadministration in two patients. Thesesmall foci were of high signal inten-sity on T2-weighted images and were

of isoattenuation or low attenuationon contrast-enhanced CT scans. Inaddition, two EMCs showed exten-sive central areas of low attenuation

on contrast-enhanced CT scans, andfive of six tumors displayed enhance-ment, especially peripherally, com-pared with precontrast CT scans (Figs2c,3).

Angiography showed neovascular-ity, particularly peripherally (Fig 2d),sometimes with arteriovenous shunt-

C. d. e.

Volume 186 #{149}Number 3 Radiology #{149}821

ing. Although contrast-enhanced MR

imaging was not performed in either

of these patients, contrast-enhanced

CT demonstrated peripheral en-

hancement in both patients.After preoperative chemotherapy,

EMC in the three pediatric patients

showed a substantial decrease in sur-face area at CT and MR imaging (ie,

50% or greater decrease in surfacearea; World Health Organization cri-

tena). In the three adults who re-

ceived preoperative chemotherapy,

two tumors substantially increased in

size (ie, 25% or greater increase in sur-

face area; World Health Organization

criteria). The third mass diminished insize at CT and MR imaging, but not

substantially, and became calcified(Fig 2f-2h). Despite complete surgical

excision, this tumor subsequently me-tastasized to the lungs. Metastases,whether pulmonary (all adults) or

epidural and soft-tissue (one adult),

were noncalcified on conventional

radiographs and CT scans. Recurrent

tumors, present only in the adults,demonstrated the same imaging fea-

tures as primary EMC.

Review of histopathologic slidesfrom initial biopsy specimens andthe subsequent surgical specimens

demonstrated the typical bimorphic

pattern of EMC with two distinctivefeatures in six of seven patients:(a) nodules of moderately differenti-ated or well-differentiated cartilage,sometimes with areas of necrosis andenchondral and dysmorphic calcifica-tion, and (b) sheets of undifferen-tiated small round or spindle cellsfrequently arranged in a hemangio-pericytoma-like pattern with cells

clustered around vascular spaces (Figs

ic-le). The seventh tumor, which

showed neovascularity at angiogra-phy, peripheral enhancement at CT,

and high signal intensity at T2-weighted

MR imaging prior to biopsy, appearedto be a hemangiopericytoma at initialsuperficial biopsy, because no carti-

lage was found. Microscopic examina-

tion of more extensive biopsy speci-mens revealed the moderately welldifferentiated cartilage and thehemangiopericytoid, undifferentiatedmesenchymal cells (Fig 2e), and a di-agnosis of EMC could be established.

Figure 1. EMC of the neck extending intothe mediastinum in a 6-year-old girl. (a) An-teroposterior radiograph and (b) tomo-gram show a soft-tissue mass with stippledand ringlike calcifications (arrows in b).(c-e) Photomicrographs show the typicalfindings of EMC with undifferentiated mes-

enchymal tissue (arrowheads) around differ-entiated cartilage (arrows), some of which iscalcified. (Hematoxylin-eosin; original mag-nifications, x8 [cJ, x50 [dJ, and xiOO [eJ.)

In two patients, surgical and grosspathology reports described extensive

areas of necrosis in the EMC. Initial

and preoperative CT after chemother-apy demonstrated extensive areas of

low attenuation (Fig 3).At histopathologic examination,

metastases and recurrences both man-ifested the same bimorphic pattern asthe primary lesion; none underwent

dedifferentiation.In contrast to the similarity be-

tween the imaging and histopatho-logic findings in both adults and chil-dren, the clinical course in these twoage groups differed considerably.

Only the adult had local recurrences

and metastases, and all adults died(Table 1). Two of the three childrenwere living and well at the end of thestudy; the third child, who died ofchemotherapeutic-induced leukemia,had no evidence of recurrent or meta-

static EMC.

DISCUSSION

In contrast to conventional chon-drosarcoma, in which only 1% of tu-

Imaging Modality FindingsNo. of Patientswith Finding*

Conventional radiography (n = 7) Soft-tissue mass;calcifications (rings, arcs, slip-pled, highly opaque)

74

Conventional tomography (ii = 1) Soft-tissue mass;calcthcations (rings, arcs, stip-

pled, highly opaque)

II

Angiography (n = 2) Soft-tissue mass;neovascularity, particularly pe-ripherally

22

CTNonenhanced CT and contrast- Soft-tissue mass; 6

enhanced CT (n = 6) calcifications (rings, arcs, slip-pled, highly opaque)

4

Contrast-enhanced CT (n = 6) Lobulation;enhancement, particularly pe-ripherally;central, focal areas of low attenu-ation

65

3

MR imagingAll spin-echo sequences (n = 4) Lobulated soft-tissue mass;

signalvoids compatible with cal-cifications

42

Nonenhanced sequences (n =4)Ti-weighted sequence Low signal intensity isointense to

muscle4

Proton-density- and T2- Mass with high signal intensity 4weighted sequence greater than that of muscle

Gadolinium-enhanced Ti- Enhancing, high-signal-intensity 2weighted sequence (n = 2) mass with central foci oflow sig-

nal intensity


mors are extraskeletal, mesenchymal

chondrosarcoma develops in the softtissues in almost half of reported cases

(2-18). EMC, however, is an uncom-mon tumor; in a Mayo Clinic study,the ratio of the number of conven-tional chondrosarcomas of bone toEMC was 4i to one (4). EMC differsfrom skeletal and extraskeletal con-ventional chondrosarcomas in bothsex distribution and site of origin. InEMC, there is a slight female predom-inance (2-17), whereas men predomi-nate in skeletal and extraskeletal con-ventional chondrosarcoma (7,19). In1 14 patients (Table 3), EMC originatedmost frequently in the brain and me-ninges and in the soft tissues of theface and of the lower extremity,whereas skeletal and extraskeletalconventional chondrosarcomas aremost commonly found in the pelvisand femur (7,19).

EMC has two peak age incidencesin the adult, depending on its loca-tion: at 23.5 (range, 5-48) years withcentral nervous system involvementand at 43.9 (range, 21-62) years with

soft-tissue and/or muscular involve-

ment (9). Our adult population corre-lated with the older age group. Noneof our patients had meningeal or cere-bral tumors, but one developed extra-dural metastases. To our knowledge,only 10 cases of EMC have been re-

ported in children, including ourthree patients. Of five children whohad meningeal or cerebral EMC, twowere living 7 and 9 years after sur-gery; three had no long-term fol-low-up (9). One 8-month-old infanthad a noncalcified soft-tissue mass inthe lower neck and mediastinum thatenlarged the lower cervical neuralforamina and produced extraduraldefects at myelography. This infantdied I month after surgery; no au-topsy was performed (5). A 15-year-old adolescent, who had a chest wall

mass treated with surgery and adju-

vant chemotherapy, was living free ofdisease 10 years after surgery (7; Hu-vos AG, personal communication,1992).

The long-term survival of patientswith EMC is difficult to evaluate, be-cause most series combine the skeletaland extraskeletal forms in their data.In the two largest combined series,5-year survival was 42% (7) to 54.6%(10) and 10-year survival was 27.3%(10) to 28% (7). Recurrences or metas-

tases have occasionally been reported

in a patient 10-20 years after diagno-

sis; therefore, careful long-term sur-veillance is essential (10). Because re-currence may be a late event, theultimate prognostic significance of a

Table 2

Imaging Findings of EMC at Presentation

5-year survival is limited. In our se-ries, the clinical course of the adultsand children differed markedly. The

adults developed unrelenting recur-

rences and metastases, and all died.

In contrast, the small children had amore benign course without recur-

rences or metastases. The prognosticsignificance of our clinical findings is

uncertain because of the small size ofour patient population and the lengthof follow-up (6-10 years), which maybe insufficient for surveillance of this

tumor.

The imaging findings of calcifica-tion, enhancement, neovascularity,

and lobulation, although not specific

for EMC, may reflect the pathologicmorphology of EMC with its small,firm, blue-gray nodules of cartilage

interspersed within soft, white, fleshy

vascular tissue that is lobulated intwo-thirds of cases (3,4,6). Fifty per-cent to 100% of EMCs demonstrate

arc, ring, stippled, and highly opaque

calcifications at conventional radiog-

raphy and CT (3,4,6-8,10,11,13,14,16,17), and histopathologic findingsof EMC show calcification in cartilagi-

nous and reactive osteoid, particularlyin the central part of the tumor (3,4,6).Benign and malignant skeletal andextraskeletal cartilaginous tumors

may also show similar calcifications

(17,20-22). The uncommon extraskele-

tal conventional chondrosarcomamay develop calcifications that mimicEMC when well-differentiated butusually does not calcify when myxoidin type (19).

Synovial sarcomas and malignantfibrous histiocytomas show stippledand highly opaque calcifications morefrequently than EMC, although chon-droid calcifications are unusual inthese tumors. The rare extraskeletalosteosarcoma may also show scat-tered or highly opaque calcifications(23). A benign process, myositis ossifi-

cans, early in its development, maysimulate a calcified soft-tissue sar-coma. Initially, myositis ossificansmay appear at radiography as a soft-tissue mass with irregular calcification

corresponding to fibroblastic prolifer-ation and immature bone at histo-pathologic examination (24). Later, asthe lesion matures, the typical zonalpattern evolves with radiographicand CT findings of well-defined, pe-ripheral calcifications surrounding acentral area of low opacity (low atten-uation at CT), which correlate withhistopathologic findings of peripheralmature lamellar bone and osteoidaround central cellular growth (24).

Two other imaging findings ofEMC, its lobular configuration andsignal intensity patterns, are also MR

imaging features of skeletal cartilagi-

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d.


e.

nous tumors, both benign and malig-

nant, and certain soft-tissue tumorssuch as synovial sarcoma (21,25-28).

Similar to EMC, synovial sarcoma

may be lobulated, usually manifests ahigh signal intensity on T2-weightedimages, and may show inhomoge-

neous enhancement at gadolinium-enhanced MR imaging. A recentstudy suggested that MR imaging

may help in distinguishing among thevarious types of cartilaginous tumors

(25). On T2-weighted images, the sig-

nal intensity of cartilaginous tumorsvaries with the cellularity. Cartilagi-

nous tumors that have a more cellular

matrix, such as clear-cell chondrosar-

coma or chondroblastoma, are isoin-tense or hypointense to muscle tissue

on T2-weighted images and have amore amorphous configuration (25).On the other hand, the more lobu-

lated, cartilaginous lesions with lesscellular hyaline matrix such as well-differentiated chondrosarcomas and

enchondromas display homogeneoushigh signal intensity that is thought toreflect their hyaline cartilage matrix,with its low cellularity and high watercontent (25). These hyaline cartilagi-nous tumors also show low-signal-

intensity fibrous septa separating thelobules.

Like the paucicellular cartilaginoustumors, EMC also appears as a high-signal-intensity, lobulated mass on

T2-weighted images. In contrast to

these tumors, however, EMC is com-

posed predominantly of sheets of un-

differentiated mesenchymal cells,with the differentiated cartilaginouscomponent usually comprising onlya small percentage of the lesion, al-

though rarely it may constitute up tohalf the tumor area (29). The high sig-nal intensity in EMC, therefore, prob-

ably results from both the vascularundifferentiated mesenchyme andthe foci of differentiated cartilage.

In reports on skeletal chondrosarco-mas, the addition of gadolinium also

helps to distinguish the differentiatedchondrosarcomas from the more vas-

I Figure 2. EMC of the left thigh in a 43-year-old woman. Before chemotherapy, axial(a) proton-density-weighted (2,000/40) and(b) T2-weighted (2,000/80) MR images showa high-signal-intensity mass with lobulations

(arrows), (c) axial CT image shows a largemass with some peripheral enhancement

(arrows), and (d) anteroposterior femoralangiogram shows neovascularity (arrows).The initial histopathologic specimen demon-strated only vascular tissue, and the tumorwas misdiagnosed as a hemangioperictyoma.(e) Photomicrograph of a specimen from thesecond biopsy shows the bimorphic patternof EMC with moderately well differentiatedcartilage (top) and undifferentiated mesen-chymal cells around vascular spaces (bot-

tom). (Hematoxylin-eosin; original magnifi-cation, x 100.) (Fig 2 continues.)

cular, cellular chondrosarcomas. Inthe lower-grade chondrosarcomas ofbone, the thin septa surrounding thelobules, and not the lobules them-selves, become enhanced (27,28). In

contrast, the more cellular, vascular

high-grade chondrosarcomas andmesenchymal chondrosarcoma be-

come enhanced throughout the le-sions, although often inhomoge-neously (27).

In our patients with EMC, contrast-enhanced Ti-weighted MR imagingrevealed enhancing, lobulated tumorswith central foci of low signal inten-sity. At CT, these foci were of low at-tenuation or isoattenuation to muscleand could represent differentiatedcartilage with or without necrosis(20,21). Because of the small number

of patients studied and the retro-spective nature of our study without

comparative pathologic data and im-aging in the same plane of section,however, the imaging-histopatho-logic correlations are somewhatspeculative.

The enhancement at CT and MRimaging and the neovascularity at

large areas of low attenuation. At histopathologic examination, the

tumor was composed of vascular undifferentiated mesenchyme, dif-

ferentiated cartilage, and extensive areas of central necrosis.


f. g. h.

Figure 2 (continued). After chemotherapy, (f) axial CT image shows calcification of the lobulations and (g) axial proton-density-weighted

(2,000/40) and (h) T2-weighted (2,000/80) MR images demonstrate a decrease in size of the high-signal-intensity mass, with signal voids from

the calcifications.

angiography also suggest the vascular

nature of EMC (16,29,30) with its

“hemangiopericytoid” undifferenti-

ated mesenchyme. In one report, anintracranial EMC mimicked an arte-

riovenous malformation (11). Because

of its neovascularity and arteriove-

nous shunting, EMC may also be con-fused with other vascular soft-tissue

tumors such as hemangiopericytoma,

malignant histiocytoma, and synovial

sarcoma (29).To summarize the role of the differ-

ent modalities for imaging EMC, MRimaging (nonenhanced combined

with contrast-enhanced sequences)was more helpful for identifying en-

hancement, lobulation, and the extent

of lesions than was CT but could not

help in characterizing the calcifica-

tions. Conventional radiography de-lineated the type of calcifications al-

though CT more completely showed

the extent of these calcifications. The

imaging protocol for EMC should be

similar to that for other soft-tissuetumors. Conventional radiographs arefirst obtained for defining the pres-

ence and type of calcifications and for

determining any skeletal involve-

ment. Nonenhanced MR imaging isthe best procedure for demonstratingthe configuration of the tumor and

extent of the mass and for confirming

its extraskeletal location. When the

tumor has cartilaginous-type calcifica-

tions and lobulation and is extraskele-

tal, contrast-enhanced MR imaging

may help in differentiating the low-

grade chondrosarcoma, with its en-

hancement limited to the septa from

EMC and high-grade chondrosar-

coma, with their more diffuse tu-moral enhancement.

The histopathologist may also mis-

take EMC for other musculoskeletal

tumors such as hemangiopencytoma,

Ewing sarcoma, synovial sarcoma, or

dedifferentiated chondrosarcoma,

particularly with superficial or in-

adequate biopsy specimens. The pres-ence of cartilage in biopsy specimens,

however, excludes the diagnosis ofhemangiopericytoma and Ewing sar-

coma and makes synovial sarcoma

unlikely (10). The only reported caseof a “hemangiopericytoma withcartilage” was subsequently proved tobe a mesenchymal chondrosarcoma

(3). Electron microscopic studies help

further in differentiating EMC from

hemangiopericytoma by demonstrat-ing that undifferentiated mesenchy-

mal tumor cells, not pericytes, border

the vascular spaces in EMC (31,32).Although Ewing sarcoma demon-strates broad sheets of small cells simi-

lar to those of EMC, it does not formcartilage and lacks spindle cells. In

contrast to EMC, cartilaginous forma-

tion in synovial sarcoma is infrequent

compared with calcification or ossifi-

cation (4). Furthermore, synovial tu-mors characteristically show a bipha-

sic pattern with glandular tissue and

spindle-cell proliferation distinctiveof EMC (10). Dedifferentiated chon-drosarcoma differs from EMC in thatthe dedifferentiated component issharply separated from the areas of

well-differentiated tumor (8). Thus,when differentiated cartilage is inter-spersed within undifferentiated mes-

enchyme, the histopathologic find-

ings are definitive for EMC.

Recurrences in EMC may rarely

become spindle-cell tumors withoutcartilaginous elements, suggestive of

dedifferentiation into a fibrosarcoma

C.


Figure 4. Recurrence in a 38-year-old woman 4 months after surgeryfor an EMC of the buttocks and thigh. (a) Axial Ti-weighted (600/20)MR image shows a lobulated low-signal-intensity mass that is shown ashigh signal intensity on (b) a T2-weighted (2000/80) MR image. (c) On a

gadolinium-enhanced Ti-weighted (600/20) MR image, the massbecomes enhanced except for low-signal-intensity areas (arrows). Histo-pathologic examination demonstrated the two characteristic compo-nents of EMC with predominantly vascular undifferentiated mesenchy-mal tissue surrounding foci of well-differentiated cartilage.

Table 3

Origin of EMC in 114 Patients

SiteNo. of

Patients

Central (n = 70)Brain and meninges 38Face 10Neck and larynx 4Thorax and axilla 6Lumbar region 7Pelvis 5

Peripheral (n = 44)Arm 4Forearm 5

Thigh 18Calf 15Soft tissues of foot and

ankle 2

Total 114

Note-Includes patients in present study.

(6), but no specific imaging findings

have been described. None of our pa-

tients had dedifferentiated recur-rences or metastases.

In EMC, both the undifferentiatedmesenchymal cell and the differenti-ated cartilage are thought to arise

from primitive cartilage-forming mes-

enchyme (1). EMC is considered to be

a tumor in which oncogenesis recapit-

ulates fetal chondrogenesis at histo-

pathologic and immunohistochemicalstudies (18,33,34). Experimental data

about fetal rats demonstrate that the

histopathologic growth pattern of

EMC closely parallels the centripetaldifferentiation of cartilage in the fetalrat (33; Burgos-Bretones J, Rivera-Po-mar JM, personal communication,1992). In both EMC and the fetal

model, peripheral undifferentiatedmesenchymal cells proliferate in vas-cular tissue around differentiatedcentral cartilaginous foci (33). Immu-nohistochemical studies further eluci-date the similarities between fetal car-tilage development and maturationand EMC (18,34). The three stages offetal cartilage development (undiffer-entiated mesenchyme, transitionalcartilage, and mature lacunar carti-lage), express leu-7 antigen, suggest-ing a continuum of cell line. Similarly,both components of EMC (the undif-

ferentiated mesenchyme and the dif-ferentiated lacunar cartilage) are posi-

tive for leu-7 antigen (18). Furthermore,the lacunar differentiated cartilage offetus and tumor show positivity for

S-100 protein, whereas the undiffer-entiated mesenchymal cells in bothdo not (18,34). Thus, the concordanceof histopathologic findings and ofantigenic determinants leu-7 and5-100 in EMC and fetal cartilage mayindicate that this tumor is indeed anembryonic cartilage analogue(17,33,34).

In conclusion, EMC is a rare soft-tissue tumor that shares imagingfindings with other skeletal and soft-tissue tumors. Chondroid-type calcifi-

cations and lobulation are features ofboth benign and malignant cartilagi-nous tumors although these tumorsare unusual in an extraskeletal loca-tion. Lobulation and inhomogeneousenhancement may be found in syno-vial sarcoma, and neovascularity maybe found in hemangiopericytoma,malignant fibrous histiocytoma, syno-vial sarcoma, and high-grade chon-drosarcoma. Although the imagingfindings of lobulated, enhancingmasses with foci of low signal inten-sity at MR imaging and with cartilagi-

nous calcifications on plain radio-graphs and CT scans are not specific

for EMC, they could reflect its uniquehistopathologic characteristics of vas-cular undifferentiated mesenchyme

surrounding foci of differentiatedcartilage. #{149}

Acknowledgments: We express our sincereappreciation to K. Krishnan Unni, MB, BS, andAndrew C. Huvos, MD, for the clinical fol-low-up information about their patients and toJ. Burgos-Bretones, MD, and J. M. Rivera-Pomar,MD, for their comments about fetal chondro-genesis.

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Extraskeletal mesenchymal chondrosarcoma