Clinical Radiology (1992) 46, 248 252
Benign Mimics of Soft Tissue Sarcomas E. MOSKOVIC, J. W. SERPELL*, C. PARSONS, C. F I S H E R ? and J. M. T H O M A S *
Departments of Diagnostic Radiology, *Surgery and ~Histopathology, Sarcoma Unit, Royal Marsden Hospital, London We reviewed all new patients referred for treatment to the Sarcoma Unit at the Royal Marsden Hospital with a clinical diagnosis of soft tissue sarcoma (STS) during the course of 1 year (1989-1990). Of 118 patients, 65 (55.1%) had primary STS, 26 (22.0%) had recurrent STS, 19 (16.1%) had benign soft tissue turnouts and eight (6.8%) had malignant tnmours other than STS involving soft tissues and presenting clinically as soft tissue turnouts. All patients underwent CT scanning which was used to assist diagnosis, assess operability or for radiotherapy planning. The CT findings of the benign lesions, all clinically suspicious of sarcoma, are discussed. The role of CT in the identification and management of these cases is emphasized. Moskovic, E., Serpell, J.W., Parsons, C., Fisher, C. & Thomas, J.M. (1992). Clinical Radiology 46, 248 252. Benign Mimics of Soft Tissue Sarcomas
Accepted for Publication 2 June 1992
Soft tissue sarcomas (STS) are rare; they comprise less than 1% of all malignant turnouts with approximately 1000 new cases arising each year in the U K [1]. The commonest clinical presentation is that of an enlarging mass, usually within a lower extremity [2], but their rarity, diverse biological behaviour and heterogeneous histological appearances may give rise to considerable diagnostic difficulty. Cross-sectional imaging techniques such as CT and more recently M R I provide excellent definition of such soft tissue tumours, aiding both diagnosis and prediction of operability [3-7]. Although in general the histological spectrum of sarcoma subtypes cannot be reliably differentiated radiologically, certain CT characteristics can be ascribed to them both as a group and individually. This allows the radiologist some confidence in separating sarcomas from other soft tissue tumours [8-12]. In general the management of an enlarging soft tissue mass, clinically suggestive of a sarcoma, requires a firm histological diagnosis. However, recognition of radiological features indicative of either a benign tumour, or an alternative malignancy, may change the investigative algorithm. This review was undertaken to explore the radiologieal appearances of benign conditions which clinically mimic soft tissue sarcomas.
soft tissue pathology. The radiological features of the benign masses were recorded emphasizing the anatomical location, boundary definition, homogeneity of density, uniformity of contrast enhancement, presence of calcification, evidence of bone invasion and the vascular and neural relationships. RESULTS Of 118 patients referred to the R M H Sarcoma Unit during the !2 month period of the study, 65 (55.1%) had primary STS, 26 (22.0%) had recurrent STS, 19 (16. 1%) had benign soft tissue masses and eight (6.8%) had malignant tumours other than STS (Table 1). The histologies of the benign lesions are listed in Table 2, and the radiological features are outlined in Table 3. Table l - Pathological diagnosis of all referrals to S a r c o m a Unit
Histology
% Total
Soft tissue sarcoma primary recurrent
65 26
55.1 22.0
Benign soft tissue tumours
19
16.1
8
6.8
P A T I E N T S AND M E T H O D S
Malignant tumours (other than STS)
The medical records, diagnostic CT scans and histopathology of all patients referred with a clinical diagnosis of STS to the Royal Marsden Hospital (RMH) Sarcoma Unit over a period of 1 year (1989-1990) were analysed retrospectively. The CT scan technique was tailored to the circumstances of the individual tumour taking particular account of site and size. An infusion of intravenous contrast medium was always given during scanning, to show tumour relationship to major vessels and to assess vascular enhancement. Review of the imaging findings and the pathology of biopsy specimens allowed division of patients into the following diagnostic categories: (1) STS; (2) malignant tumour other than STS; (3) benign
Total
Correspondence to: Dr Eleanor Moskovic, Senior Lecturer, Department of Diagnostic Radiology, Royal Marsden Hospital, Fulham Road, London SW3 6JJ.
No. of patients
118
100
Table 2 - Pathological diagnosis of benign lesions
Pathology Fibromatosis Lipoma Arteriovenous malformation Intramuscular myxoma Myositis ossificans Non-specific 'focal' myositis Mesenteric lymphangioma Encysted suprapatellar synovitis Chronic osteomyelitis Total
No. of patients 5 4 3 2 1 1 1 1 1 19
249
BENIGN MIMICS OF SOFT TISSUE SARCOMAS
T a b l e 3 - R a d i o l o g i e a l ( C T ) f e a t u r e s o f n o n - S T S lesions
Pathology
Density homogeneity
Calcification Contrast enhancement
Bony destruction
Marginal distinctness
Vessel/nerve Malignant involvement appearance
Fibromatosis Lipoma Arteriovenous malformation Myxoma M y o s i t i s ossificans Focal myositis Lymphangioma Osteomyelitis Suprapatellar synovitis
+ + -+ -. --.
± +
--
_+_ + -+ +
_+ NA -
+ --
--
_+ -
.
+ + + + -. _+ +
. +
.
.
.
.
. +
. -+
NA, Not applicable.
Fig. 1 - L i p o m a o f a d d u c t o r c o m p a r t m e n t o f r i g h t t h i g h , A well m a r g i n a t e d h o m o g e n e o u s m a s s o f u n i f o r m fat d e n s i t y . Fig. 3 - A r t e r i o v e n o u s m a l f o r m a t i o n o f r i g h t calf, w i t h o u t c o n t r a s t . Poorly defined, serpiginous and irregular morphology involving muscle.
Fig. 2 - I n t r a m u s c u l a r m y x o m a o f left q u a d r i c e p s m u s c l e , t h i g h ( a r r o w e d ) . A well d e f i n e d l o w - a t t e n u a t i o n h o m o g e n e o u s m a s s w i t h n o infiltrative features.
The lipomas (Fig. 1) were uniformly of fat density ( - 60 to - 120 HU), showed no contrast enhancement and had clearly defined margins without infiltrative features. Similarly, the intramuscular myxomas had sharply defined boundaries, a homogenous low attenuation value (in the range + 10 to + 30 HU) and no contrast enhancement (Fig. 2). Three cases of peripheral arteriovenous malformation (buttock, calf, thigh) showed a distinctive serpiginous morphology, areas of mottling and dense, poorly marginated contrast enhancement (Fig. 3). The CT findings ofsuprapatellar synovitis were diagnostic o f a benign synovial condition, with a fluid-filled bursa related to the joint.
Fig. 4 - M y o s i t i s o s s i f i c a n s c i r c u m s c r i p t a o f t h e left t h i g h . A d i s c r e t e p e r i p h e r a l l y calcified m a s s , w i t h n o i n v a s i v e f e a t u r e s .
Fig. 5 - F o c a l m y o s i t i s o f r i g h t c a l f ( b i o p s y scan). T h e c a l f m u s c l e s a r e diffusely i n f i l t r a t e d b y fat, w i t h n o d i s c r e t e s o f t t i s s u e m a s s .
250
CLINICAL RADIOLOGY
(a)
Two rare conditions, in which the CT appearances were characteristic o f benign pathology were myositis ossificans and focal myositis. The 18-year-old male patient with myositis ossificans was referred with a 6 week history of a firm, tender mass in the upper thigh and an enlarged lymph node in the groin. CT demonstrated a well defined peripherally calcified mass in the adductor compartment of the left thigh (Fig. 4), without disruption of the surrounding fascial planes. The neurovascular structures were not involved. The patient with focal myositis of the calf was a 60-year-old man with a 4 month history of enlargement and weakness of the right calf. CT revealed poorly defined diffuse atrophy of the gastrocnemius muscle with fatty infiltration of the muscle fibres (Fig. 5). The histologically benign conditions which were more difficult to differentiate from malignancy on CT criteria were fibromatosis and mesenteric lymphangioma. The cases offibromatosis (Figs 6a, b) all showed a mass of homogenous soft tissue density ( + 30 to + 50 HU) with homogenous, often dense contrast enhancement. The masses had poorly defined margins sometimes infiltrating the surrounding tissue planes. The rnesenteric cavernous lymphangioma was demonstrated as a diffuse, low attenuation mass infiltrating the fat of the mesentery of the small intestine and right hemicolon (Fig. 7). Accurate density readings were impossible because of the close relationship with mesenteric fat. The mass was not directly infiltrating bowel wall but it did surround mesenteric vessels.
DISCUSSION (b) Fig. 6 - (a) Fibromatosis of right sacrospinalis muscle (arrowed). An isodense homogeneous mass with well defined margins. (b) Fibromatosis of right adductor origin (arrowed). A slightly hypodense homogeneous mass expanding uniformly.
Most soft tissue sarcomas have fairly characteristic appearances at CT and the presence of certain features permits some, albeit limited, pathological specificity. Malignant fibrous histiocytoma, leiomyosarcoma, synovial sarcoma and undifferentiated sarcoma types usually form irregular masses of soft tissue density which compress and then infiltrate adjacent tissue planes. This expanding sarcoma mass may create a surrounding 'pseudocapsule' particularly within limb muscles. After administration of contrast medium these tumours enhance often leaving an irregular low density, necrotic centre [3,4,7,8]. Liposarcomas also have characteristic features with intermediate or high grade tumour containing a good deal of soft tissue in addition to fat. The low grade liposarcomas are comprised solely of fat perhaps with a small number of septae. Soft tissue sarcomas rarely metastasize to regional lymph nodes or erode adjacent bones [8 12]. Although biopsy is mandatory to establish the diagnosis in most lesions, key pointers to the aetiology of non-malignant tumours can often be provided by careful analysis of their radiological features. More than 20% of clinical referrals to the Sarcoma Unit were histologically non-STS masses, which highlights the need for radiological awareness of alternative diagnoses.
D I A G N O S I S OF B E N I G N T U M O U R S
Fig. 7 - Lymphangioma of mesentery compressing right hemicolon (arrowed). A poorly defined infiltrative lesion.
Although simple intermuscular lipomas can be diagnosed with a degree of confidence, it may be hard to distinguish a low grade liposarcoma from a benign lipoma on the CT findings alone. The key differentiating
BENIGN MIMICS OF SOFT TISSUE SARCOMAS
feature betweeh lipomas and intermediate or high grade liposarcomas is the presence of an additional soft tissue component, above the density of fat, in the malignant group [ 10,11,13-15]. Increasing malignancy is identified by inhomogeneity of density, irregularity of internal septation, and contrast enhancement. 'Tru-cut' biopsy can be difficult for even the most experienced sarcoma histopathologist to interpret with certainty and false negative benign interpretation may result from unrepresentative sampling. A very rare benign lesion with established CT appearances is the intramuscular myxoma. This mesenchymal lesion occurs most frequently in the interventricular system of the heart. The commonest extra cardiac site is the musculature of the thigh. As occurred in our case, the commonest clinical presentation is that of a slowly growing, painless, firm mass. Typical CT appearances are those of a well-circumscribed, homogeneous, nonenhancing tumour within skeletal muscle, with an attenuation value slightly greater than water but less than surrounding tissues. Radiologically, tumour density is similar to a myxoid liposarcoma but it displays no other malignant features. The outlook after simple excision is excellent [16-19]. Three intramuscular arteriovenous malformations (haemangioma) occurred in this series. All had a fairly long clinical history and displayed typical CT features caused by the atypical vessels and blood filled spaces. The majority of these lesions occur in the lower extremity and present clinically in the first three decades with pain, variable swelling and impaired function. Larger lesions may have an accompanying thrill or bruit. There may be associated bone and soft tissue hypertrophy. Calcification in phleboliths may be evident on plain radiographs, and the underlying bone may show porotic changes [20-22]. Both CT and M R I are extremely useful in delineating the extent of these lesions prior to treatment. Myositis ossificans circumscripta (MOC) is the term given to the localized formation of benign heterotopic ossification in muscle. This is an important diagnosis for the radiologist to consider. It occurs mainly in young adult males, usually but not invariably associated with local trauma. It most often affects the thigh, buttock, calf or shoulder. The clinical presentation is of a warm, painful swelling which gives the clinical impression of a soft tissue sarcoma and may occasionally mislead radiologically and pathologically [23 26]. The lesion evolves in a typical 'zonal' fashion with a central area of undifferentiated, highly cellular proliferation. Haemorrhage and muscle necrosis are surrounded by a rim of immature bone and osteoblasts graduating to an outer peripheral zone of mature bone which becomes radiologically calcified in about 6-8 weeks. Early biopsy of the central or middle zones reveals tissue pathologically indistinguishable from a sarcomatous process. The development of a shell-like rim of ossification is the hallmark of MOC. This feature is readily identified by CT [25 27]. Focal myositis is a benign diagnosis which can be made confidently by the radiologist. This is a rare inflammatory pseudo-tumour of unknown aetiology which affects skeletal muscle and presents as a tender enlarging soft tissue mass usually in a lower extremity. Histologically there is evidence of inflammation with focal degeneration and regeneration, fatty atrophy and perimysial fibrosis. The treatment is conservative and the lesion does not progress [28-30].
251
Mesenteric lymphangioma is a benign condition with documented radiological appearances. It is a benign congenital malformation of ectatic lymphatic channels, 95% of which arise in the neck as a cystic hygroma. The remaining 5 % are scattered throughout the body, particularly the mediastinum, retroperitoneum and related to the viscera in the mesentery and omentum [31-34]. The lesions may be multiple. In the abdominal cavity presentation depends on the size and location of the lesion. If related to the bowel it may cause bleeding, rupture, intestinal obstruction or volvulus. Lymphangiomas are typically cystic, sometimes with internal septations and there may be calcification in the wall. Only symptomatic lesions require excision. Fibromatosis has some radiological features very similar to some malignant tumours. Also known as a desmoid tumour, they are considered histologically benign but are locally aggressive with a strong tendency to recur locally (up to 70%), even following macroscopic complete excision. They are most common in females, affect all age groups and arise in musculoaponeurotic tissue particularly around the shoulder girdle, thigh and buttock. When found in the abdominal wall or mesentery they may be associated with Gardner's syndrome [35-38]. The homogenous density seen on CT prior to contrast medium and the uniform enhancement which occurs in fibromatosis are very similar to some cases of non-Hodgkin's lymphoma affecting muscle. The uniform enhancement is unlike most soft tissue sarcomas but 30% of cases of fibromatosis show a mixed pattern of enhancement [37,39]. CONCLUSION Benign soft tissue masses are more common than their malignant counterparts. We have described a group of benign lesions which were referred with the clinical label of a soft tissue sarcoma. The radiologist has a central role in the investigation of soft tissue lesions and a sound knowledge of differential diagnosis is a fundamental prerequisite to the managment of such cases. REFERENCES 1 Fisher C. Pathology of soft tissue sarcomas. In: Pinedo HM & Verweij J, eds. Treatment of soft tissue sarcomas, Chap. 1. Boston: Kluwer Academic Publishers, 1989:260-278. 2 Pilepich MV, Antoniades J. Soft tissue sarcomas. In: Perez CA & Brady LW, eds. Principles and practice of radiation ontology, Chap. 64. Philadelphia: Lippincott, 1987:1182-1198. 3 Bland KI, McCoy DM, Kinard RE, Copleland EM. Application of MRI and CT as an adjunct to the surgical management of soft tissue sarcomas. Annals" of Surgery 1987;205(5):473-481. 4 Petasnick JP, Turner DA, Charters JR, Gitelis S, Zacharias CE. Soft tissue masses of the locomotor system: comparison of MR imaging with CT. Radiology 1986;160:125-133. 5 Totty WG, Murphy WA, Lee JKT. Soft tissue tumours: MR imaging. Radiology 1986;160:135 141. 6 Davidson T, Cooke J, Parsons C, Westbury G. Pre-operative assessment of soft tissue sarcomas by computed tomography. British Journal of Surgery 1987;74:474-478. 7 Golding RP, van Zanten TEG, Vaalk J. Diagnostic imaging. In: Pinedo HM & Verweij J, eds. Treatment of soft tissue sarcomas, Chap. 2. Boston: Kluwer Academic Publishers, 1989:23 37. 8 Weekes RG, McLeod RA, Reiman HM, Pritchard DJ. CT of soft tissue neoplasms. American Journal of Roentg enology 1985; 144:355360. 9 Enneking WF. Preoperative staging of sarcomas. Cancer Treatment Symposium 1985;3:67-70.
252
CLINICAL RADIOLOGY
10 Waligore MP, Stephens DH, Soule EH, McLeod RA. Lipomatous tumors of the abdominal cavity: CT appearance and pathologic correlation. American Journal of Roentgenology 1981; 137:539 545. 11 Friedman AC, Hartman DS, Sherman J, Lautin EM, Goldman M. Computed tomography of abdominal fatty masses. Radiology 1981; 139:415-429. 12 Eilber FR, Huth JF, Mirra J, Rosen G. Progress in the recognition and treatment of soft tissue sarcomas. Cancer 1990;65:660-666. 13 Dooms GC, Hricak H, Sollitto RA, Higgins CB. Lipomatous tumors and tumors with a fatty component: MR imaging potential and comparison of MR and CT results. Radiology 1985;157:479 483. 14 Lindahl S, Markhede G, Berlin O. Computed tomography of lipomatous and myxoid tumors. Acta Radiologica Diagnosis 1985; 26(6):709-713. 15 Orson GG, Sim FH, Reiman HM, Taylor WF. Liposarcoma of the musculoskeletal system. Cancer 1987;60:1362 1370. 16 Hashimoto H, Tsuneyoshi M, Daimaru Y, Enjoji M, Shinohara N. Intramuscular myxoma: a clinicopathologic, immunohistochemical and electron microscopic study. Cancer 1985;58:740 747. 17 Shugar JMA, Som PM, Meyers RJ, Schaeffer BT. Intramuscular head and neck myxoma: report of a case and review of the literature. Laryngoscope 1987;97:105 107. 18 Jimenez T, Cintron E. Intramuscular myxoma simulating a cystic mass on CT. Orthopedics 1985;11(5):721-722. 19 Kransdorf M J, Moser RP, Jelinek, Weiss SW, Buetow PC, Berrey BH. Intramuscular myxoma: MR features. Journal of Computer Assisted Tomography 1989; 13(5):836-839. 20 Christenson JT, Gunterberg B. Intramuscular haemangioma of the extremities: is CT useful? British Journal of Surgery 1985;72:748 750. 21 Liu P, Daneman A, Stringer DA, Smith CR. CT of hemangiomas and related soft tissue lesions in children. Journal of the Canadian Association of Radiology 1986;37:248 255. 22 Kransdorf M J, McFarland DR, Moser RP, Venbrux AC. Case Report 649: arteriovenous malformation of the distal thigh with bone involvement. Skeletal Radiology 1991;20:63-65. 23 Weinstein L, Fraerman SH, Lewin P. Difficulties in the early diagnosis of myositis ossificans. Journal of the American Medical Association 1954;154(12):994 996. 24 Angervall L, Stener B, Stener I, Ahren C. Pseudomatignant osseous tumour of soft tissue. Journal of Bone and Joint Surgery 1969; 51 B(4):654-663. 25 Amendola MA, Glazer GM, Agha FP, Francis IR, Weatherbee L,
26 27 28 29 30 31 32 33 34 35 36
37 38 39
Martel W. Myositis ossificans circumscripta: CT diagnosis. Radiology 1983;149:775 779. Ackerman L, Ramamurthy S, Jablokow V, van Drunen M, Kaplan E. Case Report 488: Post-traumatic myositis ossificans mimicking a soft tissue neoplasm. Skeletal Radiology 1988; 17:3 I0 314. Fisher DR, Hinke ML, Musculoskeletal case of the day: myositis ossificans. American Journal of Roentgenology 1986; 146:1087-1093. Heffner RR, Armbrustmacher VW, Earle KM. Focal myositis. Cancer 1977;40:301-306. Liefeld PA, Ferguson AB, Fu FH. Focal myositis: a benign lesion that mimics malignant disease. Journal of Bone and Joint Surgery 1982;64(A): 1371-1373. Moskovic E, Fisher C, Westbury G, Parsons C. Focal myositis, a benign inflammatory pseudotumour: CT appearances. British Journal of Radiology 1991;64(762):489-493. Thomas AMK, Leung A, Lynn J. Abdominal cystic lymphangiomatosis: report of a case and review of the literature. British Journal of Radiology 1985;58:467-469. Ros PR, Olmstead WW, Moser RP, Dachman AH, Hjermstad BH, Sobin LH. Mesenteric and omental cysts: histologic classification with imaging correlation. Radiology 1987; 164:327 332. Cutillo DP, Swayne LC, Cocco J, Dougan H. CT and M R imaging in cystic abdominal lymphangiomatosis. Journal of Computer Assisted Tomography 1989;13(3):534-536. Davidson A J, Hartman DS. Lymphangioma of the retroperitoneum: CT and sonographic characteristics. Radiology 1990; 175:507 510. Hudson TM, Vandergriend RA, Springfield DS, Hawkins IF, Spanier SS, Enneking WF, Hamlin DJ. Aggressive fibromatosis: evaluation by CT and angiography. Radiology 1984;150:495-501. Rubenstein WA, Gray G, Auh YH, Hoing CL, Honig CL, Thorbjarnason B, Williams JJ, Haimes AB, Zirinsky K, Kazam E. CT of fibrous tissues with sonographic correlation. American Journal of Roentgenology 1985; 147:1067-1074. Francis IR, Dorovini-Zis K, Glazer GM, Lloyd RV, Amendola MA, Martel W. The fibromatoses: CT-pathologic correlation. American Journal of Roentgenology 1986;147:1063 1066. Hawnaur JM, Jenkins JPR, Isherwood I. Magnetic resonance imaging of musculoaponeurotic fibromatosis. Skeletal Radiology 1990;19:509 514. Einstein DM, Tagtiabue JR, Desai RK. Abdominal desmoids: CT findings in 25 patients, American Journal of Roentgenology 1991; 157:275-279.
Benign Mimics of Soft Tissue Sarcomas E. MOSKOVIC, J. W. SERPELL*, C. PARSONS, C. F I S H E R ? and J. M. T H O M A S *
Departments of Diagnostic Radiology, *Surgery and ~Histopathology, Sarcoma Unit, Royal Marsden Hospital, London We reviewed all new patients referred for treatment to the Sarcoma Unit at the Royal Marsden Hospital with a clinical diagnosis of soft tissue sarcoma (STS) during the course of 1 year (1989-1990). Of 118 patients, 65 (55.1%) had primary STS, 26 (22.0%) had recurrent STS, 19 (16.1%) had benign soft tissue turnouts and eight (6.8%) had malignant tnmours other than STS involving soft tissues and presenting clinically as soft tissue turnouts. All patients underwent CT scanning which was used to assist diagnosis, assess operability or for radiotherapy planning. The CT findings of the benign lesions, all clinically suspicious of sarcoma, are discussed. The role of CT in the identification and management of these cases is emphasized. Moskovic, E., Serpell, J.W., Parsons, C., Fisher, C. & Thomas, J.M. (1992). Clinical Radiology 46, 248 252. Benign Mimics of Soft Tissue Sarcomas
Accepted for Publication 2 June 1992
Soft tissue sarcomas (STS) are rare; they comprise less than 1% of all malignant turnouts with approximately 1000 new cases arising each year in the U K [1]. The commonest clinical presentation is that of an enlarging mass, usually within a lower extremity [2], but their rarity, diverse biological behaviour and heterogeneous histological appearances may give rise to considerable diagnostic difficulty. Cross-sectional imaging techniques such as CT and more recently M R I provide excellent definition of such soft tissue tumours, aiding both diagnosis and prediction of operability [3-7]. Although in general the histological spectrum of sarcoma subtypes cannot be reliably differentiated radiologically, certain CT characteristics can be ascribed to them both as a group and individually. This allows the radiologist some confidence in separating sarcomas from other soft tissue tumours [8-12]. In general the management of an enlarging soft tissue mass, clinically suggestive of a sarcoma, requires a firm histological diagnosis. However, recognition of radiological features indicative of either a benign tumour, or an alternative malignancy, may change the investigative algorithm. This review was undertaken to explore the radiologieal appearances of benign conditions which clinically mimic soft tissue sarcomas.
soft tissue pathology. The radiological features of the benign masses were recorded emphasizing the anatomical location, boundary definition, homogeneity of density, uniformity of contrast enhancement, presence of calcification, evidence of bone invasion and the vascular and neural relationships. RESULTS Of 118 patients referred to the R M H Sarcoma Unit during the !2 month period of the study, 65 (55.1%) had primary STS, 26 (22.0%) had recurrent STS, 19 (16. 1%) had benign soft tissue masses and eight (6.8%) had malignant tumours other than STS (Table 1). The histologies of the benign lesions are listed in Table 2, and the radiological features are outlined in Table 3. Table l - Pathological diagnosis of all referrals to S a r c o m a Unit
Histology
% Total
Soft tissue sarcoma primary recurrent
65 26
55.1 22.0
Benign soft tissue tumours
19
16.1
8
6.8
P A T I E N T S AND M E T H O D S
Malignant tumours (other than STS)
The medical records, diagnostic CT scans and histopathology of all patients referred with a clinical diagnosis of STS to the Royal Marsden Hospital (RMH) Sarcoma Unit over a period of 1 year (1989-1990) were analysed retrospectively. The CT scan technique was tailored to the circumstances of the individual tumour taking particular account of site and size. An infusion of intravenous contrast medium was always given during scanning, to show tumour relationship to major vessels and to assess vascular enhancement. Review of the imaging findings and the pathology of biopsy specimens allowed division of patients into the following diagnostic categories: (1) STS; (2) malignant tumour other than STS; (3) benign
Total
Correspondence to: Dr Eleanor Moskovic, Senior Lecturer, Department of Diagnostic Radiology, Royal Marsden Hospital, Fulham Road, London SW3 6JJ.
No. of patients
118
100
Table 2 - Pathological diagnosis of benign lesions
Pathology Fibromatosis Lipoma Arteriovenous malformation Intramuscular myxoma Myositis ossificans Non-specific 'focal' myositis Mesenteric lymphangioma Encysted suprapatellar synovitis Chronic osteomyelitis Total
No. of patients 5 4 3 2 1 1 1 1 1 19
249
BENIGN MIMICS OF SOFT TISSUE SARCOMAS
T a b l e 3 - R a d i o l o g i e a l ( C T ) f e a t u r e s o f n o n - S T S lesions
Pathology
Density homogeneity
Calcification Contrast enhancement
Bony destruction
Marginal distinctness
Vessel/nerve Malignant involvement appearance
Fibromatosis Lipoma Arteriovenous malformation Myxoma M y o s i t i s ossificans Focal myositis Lymphangioma Osteomyelitis Suprapatellar synovitis
+ + -+ -. --.
± +
--
_+_ + -+ +
_+ NA -
+ --
--
_+ -
.
+ + + + -. _+ +
. +
.
.
.
.
. +
. -+
NA, Not applicable.
Fig. 1 - L i p o m a o f a d d u c t o r c o m p a r t m e n t o f r i g h t t h i g h , A well m a r g i n a t e d h o m o g e n e o u s m a s s o f u n i f o r m fat d e n s i t y . Fig. 3 - A r t e r i o v e n o u s m a l f o r m a t i o n o f r i g h t calf, w i t h o u t c o n t r a s t . Poorly defined, serpiginous and irregular morphology involving muscle.
Fig. 2 - I n t r a m u s c u l a r m y x o m a o f left q u a d r i c e p s m u s c l e , t h i g h ( a r r o w e d ) . A well d e f i n e d l o w - a t t e n u a t i o n h o m o g e n e o u s m a s s w i t h n o infiltrative features.
The lipomas (Fig. 1) were uniformly of fat density ( - 60 to - 120 HU), showed no contrast enhancement and had clearly defined margins without infiltrative features. Similarly, the intramuscular myxomas had sharply defined boundaries, a homogenous low attenuation value (in the range + 10 to + 30 HU) and no contrast enhancement (Fig. 2). Three cases of peripheral arteriovenous malformation (buttock, calf, thigh) showed a distinctive serpiginous morphology, areas of mottling and dense, poorly marginated contrast enhancement (Fig. 3). The CT findings ofsuprapatellar synovitis were diagnostic o f a benign synovial condition, with a fluid-filled bursa related to the joint.
Fig. 4 - M y o s i t i s o s s i f i c a n s c i r c u m s c r i p t a o f t h e left t h i g h . A d i s c r e t e p e r i p h e r a l l y calcified m a s s , w i t h n o i n v a s i v e f e a t u r e s .
Fig. 5 - F o c a l m y o s i t i s o f r i g h t c a l f ( b i o p s y scan). T h e c a l f m u s c l e s a r e diffusely i n f i l t r a t e d b y fat, w i t h n o d i s c r e t e s o f t t i s s u e m a s s .
250
CLINICAL RADIOLOGY
(a)
Two rare conditions, in which the CT appearances were characteristic o f benign pathology were myositis ossificans and focal myositis. The 18-year-old male patient with myositis ossificans was referred with a 6 week history of a firm, tender mass in the upper thigh and an enlarged lymph node in the groin. CT demonstrated a well defined peripherally calcified mass in the adductor compartment of the left thigh (Fig. 4), without disruption of the surrounding fascial planes. The neurovascular structures were not involved. The patient with focal myositis of the calf was a 60-year-old man with a 4 month history of enlargement and weakness of the right calf. CT revealed poorly defined diffuse atrophy of the gastrocnemius muscle with fatty infiltration of the muscle fibres (Fig. 5). The histologically benign conditions which were more difficult to differentiate from malignancy on CT criteria were fibromatosis and mesenteric lymphangioma. The cases offibromatosis (Figs 6a, b) all showed a mass of homogenous soft tissue density ( + 30 to + 50 HU) with homogenous, often dense contrast enhancement. The masses had poorly defined margins sometimes infiltrating the surrounding tissue planes. The rnesenteric cavernous lymphangioma was demonstrated as a diffuse, low attenuation mass infiltrating the fat of the mesentery of the small intestine and right hemicolon (Fig. 7). Accurate density readings were impossible because of the close relationship with mesenteric fat. The mass was not directly infiltrating bowel wall but it did surround mesenteric vessels.
DISCUSSION (b) Fig. 6 - (a) Fibromatosis of right sacrospinalis muscle (arrowed). An isodense homogeneous mass with well defined margins. (b) Fibromatosis of right adductor origin (arrowed). A slightly hypodense homogeneous mass expanding uniformly.
Most soft tissue sarcomas have fairly characteristic appearances at CT and the presence of certain features permits some, albeit limited, pathological specificity. Malignant fibrous histiocytoma, leiomyosarcoma, synovial sarcoma and undifferentiated sarcoma types usually form irregular masses of soft tissue density which compress and then infiltrate adjacent tissue planes. This expanding sarcoma mass may create a surrounding 'pseudocapsule' particularly within limb muscles. After administration of contrast medium these tumours enhance often leaving an irregular low density, necrotic centre [3,4,7,8]. Liposarcomas also have characteristic features with intermediate or high grade tumour containing a good deal of soft tissue in addition to fat. The low grade liposarcomas are comprised solely of fat perhaps with a small number of septae. Soft tissue sarcomas rarely metastasize to regional lymph nodes or erode adjacent bones [8 12]. Although biopsy is mandatory to establish the diagnosis in most lesions, key pointers to the aetiology of non-malignant tumours can often be provided by careful analysis of their radiological features. More than 20% of clinical referrals to the Sarcoma Unit were histologically non-STS masses, which highlights the need for radiological awareness of alternative diagnoses.
D I A G N O S I S OF B E N I G N T U M O U R S
Fig. 7 - Lymphangioma of mesentery compressing right hemicolon (arrowed). A poorly defined infiltrative lesion.
Although simple intermuscular lipomas can be diagnosed with a degree of confidence, it may be hard to distinguish a low grade liposarcoma from a benign lipoma on the CT findings alone. The key differentiating
BENIGN MIMICS OF SOFT TISSUE SARCOMAS
feature betweeh lipomas and intermediate or high grade liposarcomas is the presence of an additional soft tissue component, above the density of fat, in the malignant group [ 10,11,13-15]. Increasing malignancy is identified by inhomogeneity of density, irregularity of internal septation, and contrast enhancement. 'Tru-cut' biopsy can be difficult for even the most experienced sarcoma histopathologist to interpret with certainty and false negative benign interpretation may result from unrepresentative sampling. A very rare benign lesion with established CT appearances is the intramuscular myxoma. This mesenchymal lesion occurs most frequently in the interventricular system of the heart. The commonest extra cardiac site is the musculature of the thigh. As occurred in our case, the commonest clinical presentation is that of a slowly growing, painless, firm mass. Typical CT appearances are those of a well-circumscribed, homogeneous, nonenhancing tumour within skeletal muscle, with an attenuation value slightly greater than water but less than surrounding tissues. Radiologically, tumour density is similar to a myxoid liposarcoma but it displays no other malignant features. The outlook after simple excision is excellent [16-19]. Three intramuscular arteriovenous malformations (haemangioma) occurred in this series. All had a fairly long clinical history and displayed typical CT features caused by the atypical vessels and blood filled spaces. The majority of these lesions occur in the lower extremity and present clinically in the first three decades with pain, variable swelling and impaired function. Larger lesions may have an accompanying thrill or bruit. There may be associated bone and soft tissue hypertrophy. Calcification in phleboliths may be evident on plain radiographs, and the underlying bone may show porotic changes [20-22]. Both CT and M R I are extremely useful in delineating the extent of these lesions prior to treatment. Myositis ossificans circumscripta (MOC) is the term given to the localized formation of benign heterotopic ossification in muscle. This is an important diagnosis for the radiologist to consider. It occurs mainly in young adult males, usually but not invariably associated with local trauma. It most often affects the thigh, buttock, calf or shoulder. The clinical presentation is of a warm, painful swelling which gives the clinical impression of a soft tissue sarcoma and may occasionally mislead radiologically and pathologically [23 26]. The lesion evolves in a typical 'zonal' fashion with a central area of undifferentiated, highly cellular proliferation. Haemorrhage and muscle necrosis are surrounded by a rim of immature bone and osteoblasts graduating to an outer peripheral zone of mature bone which becomes radiologically calcified in about 6-8 weeks. Early biopsy of the central or middle zones reveals tissue pathologically indistinguishable from a sarcomatous process. The development of a shell-like rim of ossification is the hallmark of MOC. This feature is readily identified by CT [25 27]. Focal myositis is a benign diagnosis which can be made confidently by the radiologist. This is a rare inflammatory pseudo-tumour of unknown aetiology which affects skeletal muscle and presents as a tender enlarging soft tissue mass usually in a lower extremity. Histologically there is evidence of inflammation with focal degeneration and regeneration, fatty atrophy and perimysial fibrosis. The treatment is conservative and the lesion does not progress [28-30].
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Mesenteric lymphangioma is a benign condition with documented radiological appearances. It is a benign congenital malformation of ectatic lymphatic channels, 95% of which arise in the neck as a cystic hygroma. The remaining 5 % are scattered throughout the body, particularly the mediastinum, retroperitoneum and related to the viscera in the mesentery and omentum [31-34]. The lesions may be multiple. In the abdominal cavity presentation depends on the size and location of the lesion. If related to the bowel it may cause bleeding, rupture, intestinal obstruction or volvulus. Lymphangiomas are typically cystic, sometimes with internal septations and there may be calcification in the wall. Only symptomatic lesions require excision. Fibromatosis has some radiological features very similar to some malignant tumours. Also known as a desmoid tumour, they are considered histologically benign but are locally aggressive with a strong tendency to recur locally (up to 70%), even following macroscopic complete excision. They are most common in females, affect all age groups and arise in musculoaponeurotic tissue particularly around the shoulder girdle, thigh and buttock. When found in the abdominal wall or mesentery they may be associated with Gardner's syndrome [35-38]. The homogenous density seen on CT prior to contrast medium and the uniform enhancement which occurs in fibromatosis are very similar to some cases of non-Hodgkin's lymphoma affecting muscle. The uniform enhancement is unlike most soft tissue sarcomas but 30% of cases of fibromatosis show a mixed pattern of enhancement [37,39]. CONCLUSION Benign soft tissue masses are more common than their malignant counterparts. We have described a group of benign lesions which were referred with the clinical label of a soft tissue sarcoma. The radiologist has a central role in the investigation of soft tissue lesions and a sound knowledge of differential diagnosis is a fundamental prerequisite to the managment of such cases. REFERENCES 1 Fisher C. Pathology of soft tissue sarcomas. In: Pinedo HM & Verweij J, eds. Treatment of soft tissue sarcomas, Chap. 1. Boston: Kluwer Academic Publishers, 1989:260-278. 2 Pilepich MV, Antoniades J. Soft tissue sarcomas. In: Perez CA & Brady LW, eds. Principles and practice of radiation ontology, Chap. 64. Philadelphia: Lippincott, 1987:1182-1198. 3 Bland KI, McCoy DM, Kinard RE, Copleland EM. Application of MRI and CT as an adjunct to the surgical management of soft tissue sarcomas. Annals" of Surgery 1987;205(5):473-481. 4 Petasnick JP, Turner DA, Charters JR, Gitelis S, Zacharias CE. Soft tissue masses of the locomotor system: comparison of MR imaging with CT. Radiology 1986;160:125-133. 5 Totty WG, Murphy WA, Lee JKT. Soft tissue tumours: MR imaging. Radiology 1986;160:135 141. 6 Davidson T, Cooke J, Parsons C, Westbury G. Pre-operative assessment of soft tissue sarcomas by computed tomography. British Journal of Surgery 1987;74:474-478. 7 Golding RP, van Zanten TEG, Vaalk J. Diagnostic imaging. In: Pinedo HM & Verweij J, eds. Treatment of soft tissue sarcomas, Chap. 2. Boston: Kluwer Academic Publishers, 1989:23 37. 8 Weekes RG, McLeod RA, Reiman HM, Pritchard DJ. CT of soft tissue neoplasms. American Journal of Roentg enology 1985; 144:355360. 9 Enneking WF. Preoperative staging of sarcomas. Cancer Treatment Symposium 1985;3:67-70.
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