Characterising benign fibrous soft-tissue tumours in adults: why is it so difficult and what do we need to know?

Clinical Radiology xxx (2015) e1ee14

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Review

Characterizing benign fibrous soft-tissue tumours in adults: why is it so difficult and what do we need to know? E. Ng a, A.A. Tandon a, *, B.C.S. Ho b, B.K. Chong a a b

Department of Diagnostic Radiology, Tan Tock Seng Hospital, Singapore Department of Pathology, Tan Tock Seng Hospital, Singapore

art icl e i nformat ion Article history: Received 29 September 2014 Received in revised form 28 January 2015 Accepted 5 February 2015

Fibrous, myofibroblastic, and fibrohistiocytic soft-tissue tumours are amongst the most common benign soft-tissue lesions encountered in clinical practice. They demonstrate varied biological behaviour and imaging characteristics. Benign fibroblastic lesions, such as nodular fasciitis, are small, have a self-limited course, and rarely recur after excision, whereas deep fibromatosis and plexiform fibrohistiocytic tumours tend to exhibit more aggressive features and often have high recurrence rates. MRI with its superior tissue contrast, multiplanar imaging capability, and lack of ionizing radiation is regarded as the preferred method of tumour evaluation, tissue characterization, and assessment of treatment response. Histopathological features are depicted at MRI, reflecting the amount and distribution of the cellular and fibrous matrix. Cellular tumours tend to show higher T2 signal intensity and post-contrast enhancement as compared to tumours with greater collagenous content, which appear dark and show less enhancement. Awareness of MR characteristics, pathological behaviour, and common sites of occurrence of fibrous soft-tissue tumours will help radiologists to determine the appropriate differential diagnosis and guide patient management. Ó 2015 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Introduction Fibrous, myofibroblastic, and fibrohistiocytic soft-tissue tumours represent a large subset of mesenchymal tumours that are commonly encountered in adults during clinical practice with a varied range of anatomical locations, pathological features, and biological behaviour. Despite

* Guarantor and correspondent: A. A. Tandon, Department of Diagnostic Radiology, Tan Tock Seng Hospital, Singapore. Tel.: þ65 98597657; fax: þ6563578112. E-mail address: [email protected] (A.A. Tandon).

advances in imaging, characterization of these soft-tissue lesions remains a challenging clinical problem. The World Health Organisation (WHO) classification (2013) of fibroblastic and fibrohistiocytic tumours categorized these tumours into benign, intermediate (locally aggressive and rarely metastasizing), and malignant. This review article will focus on the first two categories. These include benign fibroblastic lesions, such as nodular fasciitis, as well as intermediate lesions, such as deep fibromatosis and plexiform fibrohistiocytic tumours (PFTs), which tend to demonstrate more aggressive features. Notably amongst the intermediate-grade tumours, superficial and deep fibromatosis (desmoid tumours) fall under the “locally aggressive” subcategory whereas solitary fibrous tumours

http://dx.doi.org/10.1016/j.crad.2015.02.010 0009-9260/Ó 2015 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Ng E, et al., Characterizing benign fibrous soft-tissue tumours in adults: why is it so difficult and what do we need to know?, Clinical Radiology (2015), http://dx.doi.org/10.1016/j.crad.2015.02.010

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E. Ng et al. / Clinical Radiology xxx (2015) e1ee14

(SFTs), inflammatory myofibroblastic tumours, and PFTs are considered “rarely metastasizing”. (Table 1)

Clinical evaluation and imaging approach Careful clinical assessment of the region of concern should precede any imaging. The clinical history, age of the patient, and location of the fibrous mass are important pieces of information that when analysed with imaging findings can help to establish the diagnosis. Imaging characterization of soft-tissue tumours in general should not be limited to MRI. Plain radiography helps to distinguish hard palpable lumps caused by underlying bony deformity, such as exostosis, and also enables assessment of soft-tissue calcifications, which can be specific for certain diagnoses such as myositis ossificans and calcifying fibrous tumours in the present context. Amongst soft-tissue sarcomas, synovial sarcomas show calcifications in a large proportion of cases. Specific aggressive features, such as bony erosion or destruction and joint involvement, can also be evaluated. Sonography is useful in determining the size and consistency of a superficial soft-tissue mass. High-resolution ultrasound allows solid structures to be distinguished from cystic ones and is useful in directing percutaneous biopsy. Colour Doppler ultrasound can also evaluate the vascularity of the lesion. MRI with its superior tissue contrast, multiplanar imaging capability, and lack of ionizing radiation is regarded as the preferred method of soft-tissue tumour evaluation, tissue characterization, local staging, tumour extent, and surgical planning.1 Multiplanar imaging is very helpful in determining the anatomical extent of the lesion and its relationship to adjacent structures. Table 1 Overview of benign and intermediate fibroblastic and fibrohistiocytic softtissue tumours in adults. Benign

Intermediate Intermediate (locally aggressive) (rarely metastasizing)

Nodular fasciitis

Superficial fibromatosis Desmoids-type fibromatosis

Myositis ossificans Elastofibroma

Solitary fibrous tumor Inflammatory myofibroblastic tumor Plexiform fibrohistiocytic tumor

Fibroma of tendon sheath Desmoplastic fibroblastoma Calcifying fibrous tumor Giant Cell Tumor of tendon sheath Other benign proliferationsa Ischemic fasciitis Mammary-type myofibroblastoma Angiomyofibroblastoma Cellular angiofibroma Nuchal-type fibroma Gardner fibroma a These lesions are rarely seen on imaging and will be excluded from this article discussion.

MRI technique The present cases were examined using 1.5 or 3 T MRI systems. MRI images of the lesion should be acquired in at least two orthogonal planes, using T1-weighted and T2weighted spin-echo sequences, the latter usually with fat saturation to make the lesion more conspicuous. A shorttau inversion time recovery (STIR) sequence may be added if adequate fat suppression is a concern, but in general, it should not replace T2-weighting, which has a better signal-to-noise ratio and higher resolution. Most fibrous tumours are heterogeneous and show mixed signal intensity on T2-weighting. T2 dark regions within the tumour usually represent collagenous bands, hyalinized regions or haemosiderin deposits for cases of desmoid tumours, fibroma of the tendon sheath (FTS), and giant cell tumour of the tendon sheath (GCTTS) respectively. Gradient-echo sequences are useful for identifying haemosiderin products, which are vital in making a diagnosis of GCTTS. The additional value of T1-weighted sequences with fat suppression has been described in characterizing fibrous tumours by Gielen et al.2 but has not been confirmed. However, postcontrast T1-weighted fat-suppressed images are useful in commenting upon vascularity and margins of fibrous tumours. The dark collagenous bands show no enhancement whereas the more cellular component comprising fibroblasts and other cells show enhancement. The enhancement seen in viable tumour also allows selection of biopsy site. For surgical planning, it is crucial to determine the anatomical compartment of the lesion, whether it is intramuscular, subcutaneous, or intra-articular. Placement of a marker over the area of clinical concern is often useful to ensure that the area has been included within the field of view. MRI is also used to assess response to therapy and for recurrent disease surveillance.

Benign fibroblastic proliferations Benign fibroblastic proliferations constitute a heterogeneous group of well-defined entities. Lesions such as nodular fasciitis are cellular, tend to grow rapidly, and can simulate sarcoma. Other fibroblastic proliferations, such as elastofibromas, FTS, and keloids, are more collagenous and less cellular. Although tumours under this category may have aggressive clinical presentation, they rarely recur after resection.

Nodular fasciitis Nodular fasciitis also called pseudosarcomatous fasciitis or proliferative fasciitis is a benign soft-tissue lesion of proliferating fibroblasticemyofibroblastic cells. The lesion commonly presents as a fast-growing painful mass in the upper extremity of young adults (20e40 years age group), which may arouse suspicion of sarcoma.3 Although the cause is unknown, it may be due to a reactive process triggered by local injury or inflammation. In a recent study from the Mayo Clinic, MYH9-USP6 gene fusion was



identified in 92% of nodular fasciitis as a driving force behind its high proliferative activity and growth, suggesting an underlying neoplastic nature.4 Lesions are mostly located in the upper extremity (46%), trunk (20%), head and neck (18%), and lower extremity (16%).5 They rarely exceed 4 cm in diameter and are associated with pain or tenderness in almost half the cases. It has three forms based on lesion location (subcutaneous, fascial, and intramuscular).6,7 The subcutaneous form is the most common type. Histologically, nodular fasciitis may be myxoid, cellular, or fibrous.6,8 The type of matrix within the lesion reflects lesion age, i.e., in the early stage, the lesion contains more cellular and myxoid components, whereas in the latter stage the lesion becomes more fibrous.8 Spontaneous regression has been documented, and hence preoperative biopsy may allow a non-operative approach. However, complete local excision is usually curative. Recurrence after excision is very rare and occurs in less than 2%.9 At ultrasound, nodular fasciitis are mostly solid but may show cystic changes. At CT, this lesion has low attenuation values, reflecting its myxoid nature. The degree and distribution of myxoid and fibrous components within the lesion explain the variable T2 characteristics at MRI. Lesions with high cellular content or myxoid degeneration appear hyperintense on T2-weighted images, whereas those with highly collagenous contents are hypointense.10 In general, early lesions tend to have more myxoid component and late lesions are more fibrotic. The lesion most commonly shows mixed heterogeneous signal intensity on T2-weighted images. Perilesional soft-tissue oedema and intralesional haemosiderin deposition are not seen with nodular fasciitis. The lesion generally has signal intensity similar to or slightly hyperintense to that of skeletal muscle on T1weighted images (Fig 1aeb). Contrast enhancement is most commonly diffuse (63%), but it may also be peripheral (25%) in lesions with cystic degeneration.6 Due to rapid growth and variable MRI appearance, these lesions are often misdiagnosed as sarcomas. Moreover, the intramuscular form may sometimes be confused with earlystage myositis ossificans.

Myositis ossificans Myositis ossificans refers to the benign ectopic formation of bone in the musculature of extremities. The exact pathogenesis of this disorder is still uncertain. A history of preceding mechanical trauma occurs in half of all cases.11 The disease may occur in association with burns, stroke, and sepsis. Myositis ossificans commonly affects young adults, predominantly men, although other age groups may occasionally be involved. The limbs are affected in more than 80% of cases with quadriceps and brachialis muscles favoured in the lower and upper limbs respectively. Areas prone to injury are more commonly involved. Calcification generally develops between 4 to 6 weeks after initial trauma. Lamellar bone formation starts at the periphery and advances towards the centre in a centripetal

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pattern. CT and MRI appearances reflect this pattern of progressive maturation during the active phase of disease. At CT, the outer mature zone is ossified whereas the central immature zone appears radiolucent12 (Fig 2a). The MRI appearance of myositis ossificans changes with the age of the lesion. In the early stages, the lesion shows heterogeneous high T2 signal due to muscle necrosis and haemorrhage. An indistinct low signal-intensity rim representing calcification is seen, which enhances on contrastenhanced images.13 Proliferative myositis can be confused with the acute phase of myositis ossificans, but preservation of muscle fibres and homogeneous post-contrast enhancement seen in the former condition should help differentiate the two. After several weeks to months of progressive maturation, the lesion reveals high T1 and T2 signal intensity, which is in keeping with ossification. Late lesions typically do not enhance or may enhance minimally. In more mature lesions, the presence of high T1 and T2 signal with suppression of marrow fat on fat-saturated images mimics a lipomatous lesion. Conventional radiography and CT are superior to MRI in the evaluation of the osseous nature of the more mature lesions. Unusually, myositis ossificans may also present as a complex cystic lesion as seen in another patient (Fig 2b). The lesion, which is predominantly cystic and shows fluidefluid levels, involves the iliopsoas muscle and demonstrates a thick peripheral rim of calcification. This cystic mass-like appearance at MRI may be easily mistaken for bursitis or a neoplastic lesion. Moreover, dense mineralization may be absent in the early and mid-phases of myositis ossificans. Serial follow-up imaging may help avoid unnecessary biopsy and surgical intervention.

Elastofibroma Elastofibroma is a slow-growing fibroblastic pseudotumour most frequently encountered in older patients (usually older than 55 years) with a predilection for women.14 The classic location is between the posterior chest wall and inferior tip of scapula, deep to the latissimus dorsi and rhomboid major muscles and over the rib cage. Patients usually present with mild physical discomfort when moving the shoulder. The aetiology is thought to be due to chronic mechanical friction and bilateral lesions can be seen in up to 60% cases. Familial association has been described and discovery of chromosomal abnormalities have raised the possibility that the lesion represents a neoplastic process.15 Rarely, the lesion has been reported in extra-scapular locations such as the elbow, chest wall, hip, and gastrointestinal tract. Histologically, the lesion is composed of mainly elastin fibres with entrapped islands of fat cells. Elastofibroma at CT has attenuation similar to that of muscle. Sometimes foci of low density similar to fat can be seen within the lesion.16 The lesion can also be detected on combined positronemission tomography and CT (PET-CT) with moderate 2[18F]-fluoro-2-deoxy-D-glucose (FDG) accumulation.17


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Figure 1 (a) Nodular fasciitis in a 39-year-old woman who presented with a rapidly enlarging lump on her left wrist. (i) Axial T1-weighted MRI image shows a well-circumscribed, lobulate, subcutaneous mass of intermediate signal intensity along the volar aspect of wrist. It shows heterogeneous high signal on (ii) axial T2-weighted image and intense enhancement on (iii) T1-weighted contrast-enhanced image. (iv) Photomicrograph [haematoxylin and eosin (HE) staining 100] demonstrates short fascicular proliferation of bland spindle cells in a myxoid stroma. Scattered extravasated red blood cells are seen. (b) Intramuscular form of nodular fasciitis in another patient who presented with a painful thigh lump for 5 months. (i) Axial T1-weighted MRI image shows an isointense intramuscular lesion in the vastus lateralis muscle (orange arrow). (ii) The lesion is of mixed intermediate to bright signal intensity on T2-weighted (F/S) image. (iii) On contrast-enhanced T1weighted fat-saturation (F/S) image, the lesion shows homogeneous enhancement with a central non-enhancing area (white arrow). A neurogenic tumour can be a differential based on this MRI appearance. (iv) On colour Doppler ultrasound, which was performed prior to MRI, this lesion appears hypoechoic, demonstrates irregular margins, and shows mild internal vascularity raising concern for malignancy.

At MRI, pericapsular elastofibroma is typically a welldefined heterogeneous lentiform soft-tissue mass. The mass is predominantly composed of fibrous tissue, which has signal intensity similar to or slightly less than that of skeletal muscles on T1 and T2-weighted images. This is classically interlaced with streaks of fatty tissues, which appear bright on T1-weighted images (Fig 3). Margins may be sharp or indistinct and the size may vary. On contrastenhanced images, it may show subtle to marked enhancement thus making them non-contributory. MRI of entrapped fat with the characteristic lesion location and patient age at presentation is pathognomonic of elastofibroma.18 Local excision is curative in symptomatic lesions. No malignant transformation has been reported.

FTS FTS is an infrequently recognized tumour that has historically been difficult to distinguish from other lesions of the fingers, hands, and wrists where almost 80% of these cases occur.19,20 Rarely, FTSs are seen to arise from synovial capsule as well as fascia and aponeuroses in superficial sites21e23 (Fig 4a). It usually presents as a painless, slowgrowing hand or wrist mass in a middle-aged patient. Histologically, FTS is typically hypocellular consisting of

scattered spindle-shaped myofibroblasts embedded in dense fibrous connective tissues with slit-like vascular channels.24,25 It is considered as the end and sclerosing stage of GCTTS, probably consequential to progressive vascular impairment.26,27 At MRI, these masses are seen closely related to a tendon. They demonstrate variable signal intensity on T2-weighted images, which is based on the degree of hyalinization, sclerosis, and number of proliferating fibroblasts; more hyalinized lesions tend to be of low signal intensity, whereas more cellular lesions demonstrate high signal intensity on T2-weighted images.28 On T1-weighted images, they are generally of lower signal intensity as compared to that of skeletal muscles. These masses show variable enhancement on contrast-enhanced images, which again is dependent upon the tumour composition and vascularity. Unlike GCTTS, they lack haemosiderin-laden macrophages and hence do not bloom on gradient images. Bony involvement is very rare and occurs in less than 2%.29 FTS may readily be mistaken for nodular fasciitis due to similar age of presentation, and imaging and histological findings; however, the latter grows rapidly. Local recurrence of up to 25% has been reported30 after excision. Another case of FTS in Fig 4b shows increased T1 signal intensity in comparison to skeletal muscles. To the authors’



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Figure 2 (a) Immature phase of myositis ossificans in the left distal arm of a 39-year-old male patient. (i) Axial T1-weighted image shows an isointense lesion in the brachioradialis muscle of left distal arm with corresponding heterogeneous high signal on the T2-weighted fat-saturation image (ii). (iii) Coronal unenhanced CT image shows a hypodense lesion with peripheral calcification in the lateral aspect of the distal arm. (iv) Plain radiography also demonstrates soft-tissue calcification in the left arm (orange arrow). (b) A second unusual case of myositis ossificans, which presented as a predominantly cystic lesion in left iliopsoas muscle of a 30-year-old patient as seen in the coronal T2-weighted image (i). (ii) On gradient-echo sequence, the lesion demonstrates a thick peripheral rim of calcification and shows a fluidefluid level (white arrow). (iii) Rim enhancement is seen in the contrast-enhanced image, confirming the cystic nature of the lesion. (iv) Plain radiography shows dense calcification around the left hip joint.

knowledge, very few cases of FTS with hyperintense T1 signal intensity have been reported. The lesion also shows predominantly hyperintense signal intensity with scattered T2 dark areas on T2-weighted images, which was histologically attributed to the abundance of spindled fibroblasts in the scattered collagenous stroma.

Desmoplastic fibroblastoma (collagenous fibroma) Desmoplastic fibroblastoma usually presents as a painless, slow-growing, firm mass in the subcutaneous tissues or skeletal muscles of upper or lower extremity. It most commonly presents between the fifth and seventh decades and there is a male-female ratio of 5:1. Fascial involvement is common and up to 25% of cases involve skeletal muscles.31e33 This entity has been reported in a variety of sites but most frequently in the arm, shoulder, lower limb, back, hands, and feet; approximately 70% cases occur in the extremities.34 Histologically, these paucicellular tumours consist of stellate and spindle-shaped fibroblast-like cells that are widely separated by rich collagenous to fibromyxoid matrix.34 In addition to the lack of inciting event, rearrangement of the chromosome 11q12 breakpoint has been reported to be recurrent and unique in collagenous fibroma, confirming the neoplastic nature of the lesion.35 MRI most commonly reveals low to very low signal on T1 and T2-weighted pulse sequences with areas of T1

intermediate and T2 high signal intensity. On contrastenhanced images, there is only minimal internal enhancement due to low tumour cellularity and vascularity. These features reflect the predominant collagenous histology of these lesions. More characteristically, there is rim enhancement on MRI,36 which has been attributed to capsule-like loose fibrous tissue and a rich capillary covering, as illustrated in the case in Fig 5a. Internal calcifications and cystic changes are very uncommon in these tumours. Central dark signal intensity areas seen with desmoplastic fibromas are also evident in other collagenous lesions, such as extra-abdominal fibromatosis (desmoid tumours) and burnt-out phase of nodular fasciitis.32 However, unlike desmoid tumours, desmoplastic fibroblastomas are less cellular, less infiltrative, and do not cause bone erosions. At MRI, they do not show low signal intensity bands and are much less vascular. Clinically, collagenous fibromas present in older males whereas desmoid tumours are most common in 25e35-year-old women. Desmoplastic fibroblastomas can also be confused with giant cell tumours of the tendon sheath at MRI. The patient’s age at presentation, lesion location most commonly in the hands and feet, intense post-contrast enhancement, and blooming artefacts associated with giant cell tumours help in differentiating it from the former. Moreover, rim enhancement has not been reported in either of the abovementioned differential diagnosis.


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of occurrence include the pleura, mediastinum, and peritoneum.37e39 The MRI appearance mimics that of other fibrous lesions, such as collagenous fibroma or pigmented villonodular synovitis (PVNS), when it occurs close to a joint. The lesion is usually well-circumscribed, appearing hypointense on both T1 and T2-weighted images due to a predominance of hyalinized collagenous tissue (Fig 5b). Contrast-enhanced images may reveal mild to moderate enhancement. It lacks haemosiderin, which helps in differentiating it from PVNS. Plain films or CT usually demonstrate band-like or punctate calcifications.40 A younger age at presentation and internal calcifications are useful in distinguishing this lesion from other collagenous lesions. Another similar-appearing soft-tissue tumour that presents in younger patients and shows variable calcification is a leiomyoma. Soft-tissue leiomyomas, however, show marked post-contrast enhancement and are very rare.41 Calcifying fibrous tumours may be infrequently misdiagnosed as metastatic carcinoma, especially when they are multiple. Simple excision is usually adequate for symptomatic calcifying tumours.

GCTTS

Figure 3 Subscapular elastofibroma in a 71-year-old woman. (a) Axial T1-weighted image of the left posterior chest wall shows a crescentic mass that is deep to the rhomboid major and subscapularis muscles and appears isointense to the muscle interlaced with streaks of tiny fat signal foci (orange arrow). (b) T2-weighted image with fat suppression depicts the lesion with mildly high signal intensity. The lesion demonstrates intense enhancement on the contrast-enhanced image (c).

Treatment of desmoplastic fibroma is conservative marginal excision due to its non-aggressive behaviour. No local recurrence or metastases are reported. Hence, preoperative diagnosis would be beneficial to avoid overtreatment.

Calcifying fibrous tumour Calcifying fibrous tumour is a rare fibroblastic lesion, which is histologically characterized by fibrotic proliferation, infiltration of inflammatory cells, and dystrophic or psammomatous calcifications. The lesion is most frequently seen in children and young adults. The lesion most commonly presents as a hard, painless mass in the subcutaneous and deep soft tissues of the extremities. Other sites

GCTTS represents a localized extra-articular form of PVNS. Histologically, it is composed of multinucleated giant cells, haemosiderin deposits, and fibroblasts, and typically presents as a slow-growing mass in the third to fifth decade of life.42 It has a slight female preponderance. At MRI, GCTTS is usually seen as a longitudinally oriented mass in close relation to joints and tendons of the hands and feet. These are of low signal intensity to skeletal muscle on T1weighted sequences, and of low to intermediate signal intensity on T2-weighted sequences due to an abundance of collagenous stroma43 (Fig 6). Atypically, GCTTS can be of high signal intensity on T2-weighted fat-saturated images due to predominance of inflammatory elements.44 Blooming artefacts on gradient sequence are usually seen due to haemosiderin deposition, which is an important distinguishing feature.43e45 The presence of innumerable capillaries within the lesion results in strong post-contrast enhancement.43 Pressure erosion of the underlying bone can be seen in 10e20 % of cases.44 Internal calcification is extremely uncommon and its presence in association with a peri-articular mass should favour a diagnosis of synovial sarcoma. GCTTS closely resembles FTS at MRI, but is more common in occurrence by a ratio of 2.7:1.44 Furthermore, FTS is extremely uncommon in the lower extremities, and hence a lower extremity lesion is more likely to be a GCTTS rather than FTS.44 Pre-surgical diagnosis of GCTTS is important as it is prone to recur, with the rate of recurrence reported to be 9e44% in different studies.46

Fibromatosis Fibromatosis covers a wide range of benign fibroblastic and myofibroblastic proliferations with notable production



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Figure 4 (a) Unusual location of a histologically proven FTS in right upper arm of a 63-year-old patient. (i) T1 axial and corresponding (ii) T2 fatsupressed images show a homogeneously hypointense lesion (orange arrow) in the deep fascial plane of the arm superficial to the triceps muscles with no apparent connection to any tendon in the area. (iii) On the T1-weighted contrast-enhanced image, the lesion shows minimal enhancement. (iv) Colour Doppler ultrasound study shows a well-defined isoechoic ovoid-shaped mass underneath the subcutaneous fat, indenting the underlying muscle without any evidence of invasion. The mass shows minimal internal vascularity. (b) Another case of FTS in a 51year-old woman with a painless mass over the thenar eminence of hand. The mass appears mildly hyperintense to skeletal muscles on the axial T1-weighted image (i) and bright on the T2-weighted fat-suppressed (ii) image. Areas of low signal intensity within the lesion (white arrows) are attributable to the collagenous nature of the tumour. (iii) Photomicrograph (HE stain, 100) shows a hypocellular fibrous tumour with scattered bland fibroblasts and characteristic slit-like vasculature.

of intercellular collagen. Soft-tissue fibromatoses are categorized based on their anatomical location: superficial (fascial) or deep (musculo-aponeurotic or desmoid-type).

Superficial fibromatosis

Superficial fibromatoses are small, slow-growing lesions that arise from the fascia or aponeuroses at the palmar, plantar, penile (Peyronie’s disease), and knuckle pad locations.47 Palmar followed by plantar fibromatoses are the most common types of superficial fibromatoses.48 However, palmar fibromatoses is uncommon in Southeast Asia, the region of origin of this article. Patients with palmar fibromatoses usually present with subcutaneous nodules in the palmar aspect of fingers. These progress and become band or cord-like and cause traction deformities over time.48 It is known to occur in association with diabetes, epilepsy, and alcohol-induced liver disease.47 The MRI signal intensity of superficial fibromatoses depends upon the cellularity of lesion. They tend to be cellular and proliferative in the early clinical course and become collagenous and contractile later on. Hypocellular lesions, which are composed of dense collagen, are of low signal intensity on T1 and T2-weighted images and enhance minimally after intravenous contrast medium administration. The more cellular lesions are iso-to hypointense on T1weighted images and are of intermediate to high signal

intensity on T2-weighted images, and demonstrate diffuse post-contrast enhancement. Cellular lesions have a higher chance of recurrence after excision.48 Linear extension of the lesion along the aponeurosis (fascial tail sign) is frequently and best seen after contrast medium administration.48 Plantar fibromatosis (Ledderhose disease) usually affects the non-weight bearing medial band of the plantar aponeurosis49 (Fig 7). Its incidence increases with age and men are more frequently affected than females.48 Contracture deformities of foot are uncommon with plantar fibromatoses, unlike palmar fibromatoses.48 At MRI, well or illdefined superficial lesions are seen along the deep plantar aponeurosis, which may be inseparable from the underlying muscles. Based on the tissue composition and cellularity, the lesion may show variable signal intensity on T1 and T2weighted images.49 The presence of dense clusters of collagen appears as areas of low signal intensity. Lesions that are hyperintense to skeletal muscle on T1-weighted images may contain proteinaceous material and fat. Usually, locally aggressive fibromatosis appears bright on T2weighted images.49 Initial management is conservative with footwear modifications; surgical excision is reserved for more advanced cases but is prone to local recurrence in up to 40% of cases.48 In 10e25% of patients, the disease may be bilateral.49


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Figure 5 (a) Desmoplastic fibroblastoma in a 57-year-old woman with a painless lump over the first webspace of hand of about 3 years’ duration. Located within the belly of the first dorsal interosseous muscle, the lesion demonstrates intermediate to low signal intensity on the T1-weighted axial image (i) and diffusely hypointense signal intensity on the T2-weighted fat-saturated (ii) image. (iii) On the T1-weighted contrast-enhanced image, the lesion shows mild internal but prominent rim enhancement. It abuts the second metacarpal and second dorsal interosseous muscle and is inseparable from the extensor tendon to the index finger. No invasion of the adjacent bone is evident. (iv) Photomicrograph (HE stain, 100) demonstrates bland stellate to spindle cells scattered within the densely collagenous stroma of a desmoplastic fibroblastoma. (b) Calcifying fibrous tumour in a 28-year-old man who presented with a progressively increasing lump around the left knee. MRI shows a welldefined ovoid subcutaneous lesion anteromedially in the left knee, which appears hypointense on the T1-weighted axial image (i) and T2weighted fat-saturated image (ii) (orange arrows). Mild contrast enhancement is seen on the contrast-enhanced image (iii). The lesion abuts the medial patellar retinaculum. No deep infiltration is seen. (iv) Radiograph of the knee shows calcification within this mass (white arrow).

Desmoid-type fibromatosis (extra-abdominal or musculo-aponeurotic fibromatosis)

Deep (desmoid-type) fibromatoses lesions are larger and generally show more aggressive biological behaviour than superficial fibromatoses. Desmoid tumours are most common in the third and fourth decades and are more common in females. They have an association with familial adenomatous polyposis.50,51 Endocrine factors also play a role in their development and growth. They often present as firm, deep-seated, slow-growing soft-tissue masses in the aponeurosis and skeletal muscles, which subsequently involve adjoining neurovascular and bony structures,50 causing reduced mobility of the limb, pain, and other neurological symptoms. Lesions are usually approximately 5e10 cm in size. Although they can occur anywhere in the body, they occur most commonly in the upper extremity, chest wall, head and neck region, and around the thigh.48 At MRI, early-stage lesions like superficial fibromatoses are predominantly cellular and show increased signal intensity

on T2-weighted images.50,51 Extension into the surrounding muscles and along the fascia is frequent. Such lesions also show higher local recurrence rate after resection. Mature lesions that are relatively hypocellular demonstrate low signal intensity on T1 and T2-weighted images. In particular, low signal band-like morphology due to collagenous bands is seen in 62e91% of cases, and is helpful in making the diagnosis50,51 (Fig 8a). Extra-abdominal fibromatosis shows moderate to marked heterogeneous enhancement after contrast medium administration, making these nonenhancing collagenous bands even more distinct.50 Similar to superficial fibromatosis, the fascial tail sign is also evident in musculo-aponeurotic fibromatoses. Almost half of the lesions have well-defined margins while the remaining 50% have ill-defined margins (Fig 8b). Desmoid tumours with features such as poor margination, heterogeneous signal, and neurovascular or bony involvement can mimic soft-tissue malignancies. Bone involvement, which is more common after multiple recurrences, is seen in 6e37% of cases.48



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Figure 6 GCTTS of the flexor tendon in a 45-year-old man who presented with a non-tender lump for 1 year. MRI images reveal a lobulate, softtissue lesion wrapping the flexor tendon. It is of intermediate signal intensity on the T1-weighted image (a). It is iso-to slightly hyperintense on the T2-weighted fat-saturated image (b), demonstrates small foci of susceptibility on gradient imaging (c, orange arrow) and shows avid, heterogeneous enhancement on the contrast-enhanced image (d).

The average local recurrence rate after wide surgical excision, which is the treatment of choice, is high at around 40%.52 This also warrants close follow-up imaging at 3 to 6 months interval initially that can be later adjusted based on tumour growth and appearance of symptoms.50 Ilaslan et al.53 tried radiofrequency ablation as a viable alternative to surgical resection with some success in onerous surgical candidates.

Intermediate grade “rarely metastasizing” tumours Extrapleural solitary fibrous tumour SFTs, formerly termed haemangiopericytomas, are most commonly seen in middle-aged adults (median age 50 years) and have no predilection for either sex.54 SFTs have

Figure 7 Plantar fibromatosis in a 40-year-old man. Short axis images of the right foot reveal a (a) T1 isointense and (b) T2 intermediate to hyperintense signal intensity subcutaneous lesion stuck to the medial cord of the plantar fascia (orange arrow). (c) The lesion shows avid postcontrast enhancement. It demonstrates areas of T1 and T2 hypointensities, which are compatible with fibrous nature of the tumour. There is no infiltration of the underlying plantar muscles. (d) At ultrasound, the same nodule appears hypo-to isoechoic and causes focal fusiform bulge of the plantar fascia (white arrow). The patient had similar appearing nodules in the other foot as well. Please cite this article in press as: Ng E, et al., Characterizing benign fibrous soft-tissue tumours in adults: why is it so difficult and what do we need to know?, Clinical Radiology (2015), http://dx.doi.org/10.1016/j.crad.2015.02.010

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Figure 8 (a) Desmoid-type fibromatosis in a 47-year-old woman who presented with a painful posterior thigh swelling for 2 years, which was progressively increasing in size. T1-weighted axial image (i) shows a mass of intermediate signal intensity (orange arrow) in the lateral aspect of the posterior compartment with heterogeneously hyperintense signal intensity on the T2-weighted axial image (ii). There are thick band-like low signal intensity areas within this mass, which are suggestive of this neoplasm. (iii) The T1-weighted contrast-enhanced image demonstrates avid enhancement of the mass barring that of the low signal intensity areas. (iv) A photomicrograph (HE stain, 100) of desmoid fibromatosis shows long fascicles of cellular spindle cell tumour arranged in a fibrotic background. (b) Aggressive fibromatosis in a 45-year-old patient who presented with a painful lump in the left thigh for about 1 year. (i) T1-weighted axial image shows an intermediate signal intensity subcutaneous lesion (orange arrow) in the posterolateral aspect of the thigh with low to intermediate signal on the corresponding (ii) T2 fatsaturated axial image and homogeneous enhancement on (iii) T1 fat-saturated contrast-enhanced sequence. It is closely related to the deep fascia between the iliotibial band and the posterior compartment of the thigh with no deep extension seen.

wide anatomical distribution and can arise in any soft tissue or visceral location. Rarely large tumours can cause paraneoplastic hypoglycaemia by producing insulin-like growth factor. Most tumours present as well-circumscribed, slowgrowing, painless masses. Malignant lesions are often large (>10 cm), infiltrative, and heterogeneous.55 Typically, SFTs show patternless architecture of firmly packed spindle cells separated by thick, hyalinized collagen with branching haemangiopericytoma-like vessels. The tumour cells stain diffusely for CD 34, which helps to differentiate it from other desmoplastic tumours.55 MRI characteristics are usually non-specific with the lesion appearing isointense to muscle on T1-weighted images and hyperintense on T2-weighted images. However, this appearance along with the presence of prominent perilesional vessels and marked post-contrast enhancement are helpful in identifying this lesion,55e57 as illustrated in Fig 9. Garcia-Bennett et al.57 indicated dynamic contrastenhanced (DCE) MRI is useful in identifying potentially recurrent tumours but a formal study is needed to ascertain its role. Calcification is unusual in these tumours. A variant known as lipomatous haemangiopericytoma demonstrates intralesional fat on MRI images and needs to

be differentiated from liposarcoma.55 On imaging, SFTs may be confused with other high-grade vascular primary sarcomas or metastasis from highly vascular tumours, such as renal cell carcinoma. Percutaneous core biopsy due to its reduced risk of tumour seeding is favoured over incisional biopsy for preoperative diagnosis.55 Conceptual changes in the new WHO classification have included clearer recognition of extrapleural solitary fibrous tumours. Solitary fibrous tumour, haemangiopericytoma, lipomatous haemangiopericytoma, and giant cell angiofibroma are currently all classified under the “extrapleural solitary fibrous tumour” category and this group of tumours is now known to be associated with a recurrent NAB2STAT6 gene fusion.58

Inflammatory myofibroblastic tumour Inflammatory myofibroblastic tumours, previously known as plasma cell granulomas, histiocytomas or fibroxanthomas, are composed of both acute and chronic inflammatory cells, which include lymphocytes, plasma cells, myofibroblastic spindle cells and collagen contents due to chronic fibrous reaction. They typically occur in the



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Figure 9 Solitary fibrous tumour in a 32-year-old man who presented with a lump on the anteromedial side of the left thigh. (a) T1-weighted axial image shows a lobulate subcutaneous lesion with isointense signal intensity (orange arrow). (b) On the corresponding T2-weighted fatsaturated axial image, the lesion demonstrates heterogeneous increased signal with avid enhancement on (c) the T1-weighted contrastenhanced fat-saturated image. Prominent perilesional vessels are seen, which are helpful in making the diagnosis (white arrows). The underlying muscles are not involved. (d) A photomicrograph (HE stain, 100) demonstrates patternless bland spindle cells associated with staghornlike vasculature (black arrows). (e) The tumour cells are diffusely stained positive for CD34.

soft tissues and viscera of children and young adults, with the lung, mesentery, and omentum representing the most common sites. Only rarely do they occur in the extremities.59 At MRI, they demonstrate varied signal intensity based on predominance of certain type of cells, and have been described as great mimickers of other tumours. They are usually of intermediate to low signal intensity on T2weighted images due to the presence of myofibroblastic cells.59 CT shows the presence and type of dystrophic

calcification and bone reaction. Most commonly, there is a shell-like periosteal reaction enveloping the lesion and cortical scalloping of the adjacent bone.59 They also demonstrate increased vascularity on colour Doppler from the peripheral hypertrophied blood vessels, as evident in Fig 10a. It is also observed that these lesions are usually located close to neurovascular structures. Wide resection should be considered since there is high risk of local recurrence with possibility of malignant transformation.59


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Figure 10 (a) Inflammatory myofibroblastic tumour in a 48-year-old woman who presented with a mobile, non-tender lump over the palmar aspect of left hand. The lesion that is located in the subcutaneous fat on the thenar aspect appears isointense on (i) the T1-weighted image (orange arrow) and heterogeneously hyperintense on (ii) the T2-weighted fat-saturated image. (iii) On colour Doppler ultrasound, the lesion appears iso-to hypoechoic and demonstrates peripheral and internal vascularity. The flexor tendon is seen separate and deep to it. (b) Plexiform fibrohistiocytic tumour in a 25-year-old male who presented with paraneoplastic hypophosphotaemia and a lump in his sole. (i) Sagittal T1weighted and (ii) T2-weighted fat-saturated images show a lobulate, infiltrating low signal intensity lesion (orange arrow) in the subcutaneous layer of the sole, which shows minimal enhancement on the T1-weighted fat-saturated contrast-enhanced image (iii).

PFT PFT is a rare mesenchymal neoplasm, which preferentially occurs in adolescents and young adults.60 It most commonly presents as a painless, slow-growing mass, with a predilection for the upper extremities.61 Another less common site of occurrence is the head and neck region. At histology, PFT is composed of a mixture of small nodules and elongated fascicles that interconnect with each other, forming a characteristic plexiform arrangement.60 Multinucleated giant cells are also present. The fibroblastic subtype has resemblance to fibromatosis. When present in the foot, PFT can be clinically mistaken for plantar fibromatosis, and hence imaging is essential for making a preoperative diagnosis. At MRI, it usually presents as a poorly demarcated, superficial mass located in the subcutaneous fat or at the dermalepidermal junction61 (Fig 10b). It shows low signal intensity on both T1-weighted and T2-weighted images with only mild enhancement on contrast-enhanced images. The present case was unusual because the patient

presented with paraneoplastic syndrome, which has never been reported. PFTs frequently show local recurrence after excision, which warrants long-term follow-up. They rarely metastasize through lymphatic and vascular channels, and thus, it is important to assess for regional lymphadenopathy at initial presentation.61

Conclusion A wide spectrum of entities comes under benign fibrous soft-tissue tumours. Some lesions, such as nodular fasciitis, are benign but rapidly growing; they rarely recur after excision and may even show spontaneous regression. Whereas others such as extra-abdominal desmoid tumours are also benign but are locally infiltrative and have a high recurrence rate; they require long-term follow-up. The MRI appearance of the lesions particularly on T2weighted sequences reflects their variable histopathology. Myxoid and cellular lesions are hyperintense to muscle on



T2-weighted images, whereas lesions with collagenous contents are markedly hypointense on all sequences. Amongst the latter, hypointense band-like morphology is typically seen in desmoid-type fibromatosis. It is important for radiologists to recognize some of these characteristic appearances and the overall imaging spectrum of benign fibrous soft-tissue tumours to guide decision-making and prevent over- or under-treatment. Although histology is required in many cases, by systematically using clinical history, lesion location, and signal intensity characteristics on MRI images, the radiologist can develop appropriate differential diagnoses. MRI is also useful to determine the origin of these lesions, in defining their extent and relation to adjacent structures, and in follow-up after therapy. Musculoskeletal radiologists who are involved in the evaluation of fibrous tumours need to be aware of the modifications of the WHO nomenclature, so that it allows more uniformity in discussion with surgeons and pathology colleagues.

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