The foot is a relatively rare site of neoplastic and non-neoplastic soft tissue masses. Although it contains a rela-tively small amount of somatic soft tissue elements, thefoot is rich in tendons, fasciae, retinaculae, and synovi-um (1). In the Armed Forces Institute of Pathology se-ries[LKH1], 8% of benign soft-tissue tumors and 5% ofmalignant soft-tissue tumors occurred in the foot andankle, suggesting an unexpectedly high incidence on atissue volume basis. In general, benign tumors occur atleast 10 times more frequently than malignant soft tis-sue tumors. In one series of soft-tissue tumors of the footand ankle, 87% of lesions were benign (2).

Of all the imaging modalities, MRI demonstrates supe-

rior soft tissue characterization and is now consideredthe gold-standard imaging technique in their investiga-tion. Lately, we have encountered rare benign massesand malignant soft tissue tumors of the foot. The pre-sented cases include benign masses such as granulomaannulare, angiomyoma, neural fibrolipoma, and giantcell tumor of tendon sheath, as well as malignant tu-mors such as melanoma, synovial sarcoma, rhab-domyosarcoma and extraskeletal myxoid chondrosarco-ma. There are few published English reports addressingthe MR appearance of these masses. This pictorial essayshows MR features of uncommon soft tissue tumors ofthe foot with associated clinicopathologic findings.

Benign masses of the foot

Granuloma annulare

Granuloma annulare is an uncommon benign inflam-matory dermatosis characterized by the formation of

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MR Imaging of Uncommon Soft Tissue Tumors in the Foot: A Pictorial Essay1

Youn Joo Lee, M.D., Kyung Ah Chun, M.D., Jee Young Kim, M.D., Mi Sook Sung, M.D., Ki Tae Kim, M.D.

1Department of Radiology, The Catholic University of KoreaReceived December 21, 2006 ; Accepted March 23, 2007Address reprint requests to : Kyung Ah Chun, M.D., Department ofRadiology, The Catholic University of Korea, Uijeongbu St. Mary’sHospital, Geumo-dong, Uijeongbu city, Gyeonggi-do 480-821, Korea.Tel. 82-31-820-3137 Fax. 82-31-846-3080 E mail: ka1000@catholic.ac.kr

A large variety of masses occur in the foot. The foot is a comparatively rare site ofsoft tissue neoplasms. MRI has greatly improved the ability to detect and delineate softtissue lesions and is now considered the gold-standard imaging technique in their in-vestigation. Recently, we have encountered rare soft tissue tumors of the foot. The pre-sented cases include benign masses such as granuloma annulare, angiomyoma, neuralfibrolipoma, and giant cell tumor of tendon sheath, as well as malignant tumors suchas melanoma, synovial sarcoma, rhabdomyosarcoma and extraskeletal myxoid chon-drosarcoma. We wish to illustrate the MR findings of these uncommon soft tissue tu-mors to aid in their diagnosis.

Index words : Foot, neoplasmsNeoplasms, MRMagnetic resonance (MR), image displaySoft tissues, neoplasmsNeoplasms, diagnosis

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A B

C D

Fig. 1. Granuloma annulare in a 6-year-old boy.A. Sagittal T1-weighted image shows apoorly-defined, isointense signal inten-sity subcutaneous lesion in the dorsalaspect of the foot. B. Sagittal T2-weighted image showsheterogeneously low signal intensity.C. Sagittal post-gadolinium T1-weight-ed image with fat saturation exhibitsdiffuse enhancement of the subcuta-neous lesion.D. Photomicrograph (×100, H & Estain) shows well-circumscribed pal-isaded granuloma with granular andfibrillary, slightly basophilic material(mucin) around collagen bundles inthe foci of histiocytic aggregation.

A B

C D

Fig. 2. Giant cell tumor of tendonsheath in a 29-year-old manA, B. Axial T1-weighted (A) or sagittalT2-weighted (B) images show a largelobulated low signal intensity mass ofthe great toe. C. Enhanced coronal fat saturated T1-weighted image shows prominent en-hancement of the mass surroundingthe flexor tendon.D. Photomicrograph (×100, H & Estain) demonstrates rounded or polyg-onal cells with focal collections of xan-thoma cells and scattered multinucle-ated giant cells throughout the mass.

dermal papules with a tendency to form rings (3).Granuloma annulare represents about 2% of all benignsoft tissue masses (4). About 7% of granuloma annularepresent in the foot and ankle. There are several clinical-ly distinct forms: localized, generalized, perforating, andsubcutaneous. The localized form is the most commontype and presents as a nodular ringed skin eruption, typ-ically on the dorsum of the hands and feet, forearms,arms, legs, and thighs. It typically presents as a rapidlygrowing, solitary, painless, subcutaneous nodule. It is adisease of children and young adults, with two-thirds ofpatients presenting by age 30. The subcutaneous formpresents with rapidly growing, painless, solitary superfi-cial nodule. Lesions are most common in the pretibialregion, but may be seen in the scalp, foot, and ankle (3).

MR imaging reveals a subcutaneous mass with indis-tinct margin. This lesion has isointense signal intensityrelative to the muscle on T1-weighted images, and lowor heterogeneously hyperintense signal intensity on T2-weighted images (3). On enhanced T1-weighted images,mass shows extensive diffuse enhancement.

Giant cell tumor of tendon sheath

5-15% of giant cell tumors of tendon sheath presentin the foot and ankle, typically in the first two toes (3).Giant cell tumor of the tendon sheath represents about4% of all benign soft tissue masses (4). It usually occursin adults with a peak incidence in the third to fifth

decades and predominates in females. Pathologically, gi-ant cell tumor of tendon sheath is a highly vascular masscontaining a mixture of multinucleated giant cells withdeposition of intra-and extracellular hemosiderin due torepeated hemorrhage, as well as macrophages, fibrob-lasts, and xanthoma cells, which are the same histologicfeatures as pigmented villonodular synovitis.

The main MR feature is a well-defined mass adjacentto the tendon. Typically the mass shows low signal in-tensity on both T1-weighted and T2-weighted images,due to the paramagnetic effect of hemosiderin.

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A B

C D

Fig. 3. Angiomyoma in a 41-year-oldwomanA, B. Sagittal (A) and coronal (B) T1-weighted images show small low sig-nal intensity mass in the plantar aspectof the foot. C. Sagittal T2-weighted image with fatsaturation shows heterogeneous highsignal intensity mass.D. Enhanced coronal fat saturated T1-weighted image demonstrates inho-mogeneous strong enhancement.

Fig. 4. Neural fibrolipoma in an 8-year-old boy. Axial T1-weighted image shows heterogeneous lipomatousmass involving the second toe. Low signal areas correspond toneural tissue, while areas of high signal represent adipose tis-sue.

Gradient-echo sequences may be helpful because of theincreased magnetic susceptibility effect produced by he-mosiderin. Areas with a high proportion of xanthomacells may add regional MR characteristics of lipomatoustissue with fat-equivalent signal intensity on all pulse se-quences (1). Intense enhancement is frequently ob-served on postcontrast image (3).

Angiomyoma

The angiomyoma is a rare form of leiomyoma thatusually occurs as a solitary subcutaneous form and origi-nates in the tunica media of vessels (1). They account for5% of all benign soft tissue tumors. These tumors arefrequent in women in their fourth to sixth decades.Angiomyomas are typically small (0.5-2 cm), round, oroval tumors. The main symptoms are pain and tender-ness (3). Histologic features of angiomyoma are vascularchannels with proliferation of smooth muscle cells.

MR shows low signal intensity on T1-weighted imageand heterogeneous high signal intensity on T2-weightedimage. Hyperintense regions on T2-weighted imagedemonstrated strong enhancement on post-contrast T1-weighted image, corresponding to bundles of smoothmuscles around capillary-sized vessels. Areas with lowsignal intensity on T2-weighted image were related totough fibrous tissue, with or without hyaline degenera-tion (1).

Neural fibrolipoma

Neural fibrolipoma, also known as lipofibromatoushamartoma, perineural lipoma, and intraneural lipoma,is a benign mass composed of hypertrophied fibrofattytissues intermixed with nerve tissues. When it is associ-ated with macrodactyly, it is called macrodystrophialipomatosa. This benign condition is characterized by aunilateral, gradually enlarging mass on a distal extremi-ty during early adulthood. The upper extremity, espe-cially the median nerve is the site most often affected.Histologically, neural fibrolipoma is characterized bythe proliferation of fibrofatty elements (5).

MR shows small, cylindrical, low signal intensities onhigh signal intensity background. This represents thenerve fascicles with epineural and perineural fibrosis ona background of fatty tissue.

Malignant masses of the foot

Malignant melanoma

Malignant melanoma (melanosarcoma) is a neoplasmcontaining fibroblast-like cells, some of which containmelanin. It can arise from the skin and produce localand distant osseous destruction. Melanomas on the footare often detected at an advanced stage. Melanoma ofthe foot accounts for 3% to 15% of all cutaneousmelanomas (6).

MR shows higher and relatively homogenous signal

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A

B

C

Fig. 5. Malignant melanoma in a 79-year-old woman. A. Axial T1-weighted image shows alarge lobulated intermediate signal in-tensity mass of the great toe with adja-cent bone destruction.B. Coronal T2-weighted image exhibitssomewhat heterogeneous intermedi-ate signal intensity mass.C. Enhanced sagittal fat saturated T1-weighted image shows heterogeneousenhancement extending to the boneand dorsal subcutaneous tissue of thefoot.

intensity compared to muscle on T1-weighted image,with lower and more heterogeneous signal intensity rel-ative to muscle on T2?weighted image. Melanin causesshortening of T1 and T2 values, resulting in higher sig-nal intensity on T1-weighted and lower signal intensityon T2-weighted image. Signal intensities on T2-weight-ed image are influenced by the cellularity and the nucle-ocytoplasmatic index of the lesions, resulting in variablesignals on T2-weighted image (1).

Rhabdomyosarcoma

Rhabdomyosarcoma was originally thought to arisefrom striated muscle, but is now regarded as a primarymesenchymal tumor in which rhabdomyoblastic differ-entiation has occurred (3). Rhabdomyosarcoma com-prises approximately 20% of all soft tissue sarcomas (7).It may arise anywhere in the body, and the incidence in

the extremities is reported to be about 14% (4).Rhabdomyosarco-mas vary widely in histological ap-pearance, depending on the growth pattern, cellularity,degree of differentiation, and configuration of the indi-vidual tumor cells. Rhabdomyosarcoma is classified intothree main subgroups: embryonal, alveolar, and pleo-morphic. Embryonal is the most common type and oc-curs in the first decade of life. Embryonal rhab-domyosarcoma is composed of small cells with round orspindle-shaped hyperchromatic nuclei and varyingnumbers of larger cells that have eosinophilic cyto-plasm, which is characteristic of rhabdomyoblasts. Thealveolar subtype is more common in adolescents andyoung adults and is usually intramuscular. It is com-posed of small, round to oval cells forming nests separat-ed by fibrous connective tissue. The pleomorphic type istypically seen in adults. Pathologic diagnosis of this type

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A

B CDFig. 6. Rhabdomyosarcoma in a 42-year-old womanA. Sagittal T1-weighted image shows poorly-defined low signal intensity mass.B. Axial T2-weighted image shows high signal intensity mass with low signal strand.C. Axial post-gadolinium T1-weighted image with fat saturation reveals strong enhancement of the mass.D. Photomicrograph (×200, H & E stain) shows ill-defined aggregation of poorly-differentiated round or oval cells, and formationof irregular alveolar spaces separated and surrounded by a framework of dense fibrous septa.

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A B

C D

Fig. 8. Extraskeletal myxoid chon-drosarcoma in a 77-year-old womanA. Coronal T1-weighted image revealsa mass with poorly-defined intermedi-ate signal intensity.B. Sagittal T2-weighted image shows alobulated mass with very high signalintensity portion and internal septae.C. Coronal post-gadolinium T1-weight-ed image with fat suppression showsheterogeneous enhancement.D. Photomicrograph (×40, H & Estain) shows multiple lobules and fi-brous septae.

A B

C D

Fig. 7. Synovial sarcoma in a 38-year-old manA. Coronal T1-weighted image repre-sents a large low signal intensity masswith internal septum-like structuresand low signal intensity foci, corre-sponding to calcifications.B. Coronal T2-weighted image showsheterogeneous high signal intensitymass, reflecting the mixture of solid,cystic, fibrous and hemorrhagic ele-ments.C. Enhanced coronal T1-weighted im-age shows intense enhancement of themass.D. Sagittal T1-weighted image showsinhomogeneous signal intensity massin the plantar aspect of the foot.

is difficult due to the absence of rhabdomyoblasts andthe close resemblance to lesions of malignant fibroushistiocytoma and other pleomorphic sarcomas (3).

MR imaging shows nonspecific appearance, isointenseto muscle on T1-weighted image, hyperintense on T2-weighted image, and marked enhancement on postcon-trast image. Extremity alveolar rhabdomyosarcoma fre-quently shows prominent vascularity with serpentinehigh-flow vessels. Intralesional hemorrhage is also notunusual (3).

Synovial sarcoma

Synovial sarcoma is a well-recognized soft tissue ma-lignancy, accounting for up to 10% of all malignant mes-enchymal tumors. It is the fourth-most common soft tis-sue sarcoma after malignant fibrous histiocytoma, li-posarcoma, and rhabdomyosarcoma. Almost 25% of allsoft tissue sarcomas occur in the foot and ankle region.Synovial sarcoma is of mesenchymal origin, named forits histologic similarity to synovium (1). Since synovialsarcoma has no relationship to synovial tissue, an intra-articular location is very rare. It predominates in youngadults between 20 and 40 years, typically arises in theneighborhood of tendons, tendon sheaths, and bursae,and is less frequently related to fasciae, aponeuroses andligaments. Most synovial sarcomas present as palpablemasses, but in some cases localized pain may precedethe presence of a mass for many years. The prognosis isgenerally poor with a 5-year survival rate of 50-60%(8).

MR shows inhomogeneous signal intensity on T1- andT2-weighted images. The characteristic MR features areinfiltrative margin, solid portions, septated areas of hem-orrhage, and necrosis. Viable solid portion usually rep-resents intense contrast enhancement. Calcificationswithin the tumor are frequent. MR appearance is alsocharacterized by a peritendinous growth pattern. Thetumors are commonly found in a juxta-articular locationand are often large. However, particularly in smaller tu-mors, there is a reported tendency to present with well-defined margin and homogenous signal, possibly lead-ing to the mistaken diagnosis of a benign lesion (1).

Extraskeletal myxoid chondrosarcoma

Extraskeletal myxoid chondrosarcoma is a rare malig-nant soft tissue tumor composed of abundant myxoidmatrix and malignant chondroblastic cells (9).Extraskeletal chondrosarcomas are far less commonthan intraosseous chondrosarcomas, representing ap-

proximately 2% of all soft-tissue sarcomas. The histolog-ic types of lesions are myxoid and mesenchymal.Extraskeletal myxoid chondrosarcoma is the most com-mon histologic type of soft tissue chondrosarcoma (10).It predominates in adults aged 50-60 years, althoughpatient ages range from 4 to 92 years (9). The vast major-ity of lesions are in the extremities, with the thigh beingthe single most common location. Pathologically, the le-sions are usually surrounded by a fibrous capsule andcontain fibrous septa that divide the lesion into multiplelobules, frequently with areas of cyst formation and he-morrhage. Calcification and bone formation are not typ-ically present.

MR imaging shows a lobulated mass with hyperin-tense signal on T2-weighted image and variable signalon T1-weighted image. Extraskeletal myxoid chon-dro°°sarcoma, reflective of its extremely high watercontent, appears with very high signal intensity on T2-weighted MR image, with only mild peripheral to septalenhancement after contrast material administration(10).

Conclusion

Soft tissue masses in the foot are unusual. In this picto-rial essay, we described MR imaging features of uncom-mon benign and malignant tumors in the foot.Correlation between the MR imaging and clinicopatho-logic appearance of these masses is also addressed.Unfortunately, the MRI features of a soft tissue mass arenot always specific; however, there are cases where thediagnosis can be made or a clue provided to aid in the di-agnosis.

References

1. Waldt S, Rechl H, Rummeny EJ, Woertler K. Imaging of benignand malignant soft tissue masses of the foot. Eur Radiol 2003;13:1125-1136

2. Bos GD, Esther RJ, Woll TS. Foot tumors: diagnosis andTreatment. J Am Acad Orthop Surg 2002;10:259-270

3. Kransdorf MJ, Murphey MD. Imaging of soft tissue tumors. 2nd ed.Philadelphia: Lippincott Williams & Wilkins. 2006;299:312-321,386,563-565

4. Kransdorf MJ. Benign soft tissue tumors in a large referral popula-tion: distribution of specific diagnoses by ages, sex, and location.AJR Am J Roentgenol 1995;164:395-402

5. Ly JQ, Bui-Mansfield LT, SanDiego JW, Beaman NA, Ficke JR.Neural fibrolipoma of the foot. J Comput Assist Tomogr 2003;27:639-640

6. Gray RJ, Pckaj BA, Vega ML, Connolly SM, DiCaudo DJ, Kile TA,et al. Diagnosis and treatment of malignant melanoma of the foot.Foot Ankle Int 2006;27:696-705

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7. Suzuki Y, Ehara S, Shiraishi H, Nishida J, Murooka G, TamakawaY. Embryonal rhabdomyosarcoma of foot with expansive growthbetween metatarsals. Skeletal Radiol 1997;26:128-130

8. Nakanishi H, Araki N, Sawai Y, Kudawara I, Mano M, Ishigura S,et al. Cystic synovial sarcomas: imaging features with clinical andhistopathologic correlation. Skeletal Radiol 2003;32:701-707

9. Tateishi U, Hasegawa T, Nojima T, Takegami T, Arai Y. MRI fea-tures of extraskeletal myxoid chondrosarcoma. Skeletal Radiol2006;35:27-33

10. Murphey MD, Walker EA, Wilson AJ, Kransdorf MJ, Temple HT,Cannon FH. Imaging of primary chondrosarcoma: radiologic-pathologic correlation. Radiographics 2003;23:1245-1278

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대한영상의학회지 2007;56:585-592

발에서 드문 연부 조직 종양들의 자기공명영상소견: 임상화보1

1가톨릭대학교 의과대학 영상의학과

이윤주·천경아·김지영·성미숙·김기태

다양한 종류의 종괴들이 발에 생긴다. 발은 종양성과 비종양성의 연부 조직 종괴들이 비교적 드물게 생기는 곳

이다. 최근 자기공명영상을 통해 연부 조직 병변의 발견과 분석 능력이 크게 향상되었다. 저자들은 발에 생긴 연부

조직 종양 중 흔하지 않은 증례들을 경험하였기에 이들의 자기공명영상소견을 보고하고자 한다. 양성 종양으로는

원형 육아종(granuloma annulare), 맥관근종(angiomyoma), 신경성의 섬유지방종(neural fibrolipoma), 힘줄집의 거

세포종양(giant cell tumor of tendon sheath)이 있고 악성종양으로는 흑색종(melanoma), 윤활막 육종(synovial

sarcoma), 횡문근육종(rhabdomyosarcoma), 골외성 점액양 연골육종(extraskeletal myxoid chondrosarcoma)이

있다.