Abbreviated WHO classification of soft tissue tumors
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Tumor groups
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Benign
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Malignant
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Group 1
Adipocytic tumors
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Lipoma
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Liposarcoma
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Group 2
Fibroblastic/ myofibroblastic tumor
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Fibroma of tendon sheath
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Fibrosarcoma
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Group 3
Fibrohistiocytic tumor
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Tenosynovial giant cell tumor
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Group 4
Smooth muscle tumor
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Leiomyoma
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Leiomyosarcoma
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Group 5
Pericytic/ perivascular tumor
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Glomus tumor
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-
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Group 6
Skeletal muscle tumors
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Rhabdomyoma
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Rhabdomyosarcoma
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Group 7
Vascular tumor
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Hemangioma
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Epithelioid hemangioendothelioma
Angiosarcoma
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Group 8
Chondro-osseous tumors
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Soft tissue chondroma
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Mesenchymal chondrosarcoma
Extraskeletal osteosarcoma
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Group 10
Peripheral nerve sheath tumors
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Schwannoma
Neurofibroma
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Malignant peripheral nerve sheath tumor
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Group 11
Tumor of uncertain differentiation
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Myxoma
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Synovial sarcoma
Epithelioid sarcoma
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Group 12
Undifferentiated/ unclassified sarcoma
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-
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Undifferentiated pleomorphic sarcoma
Undifferentiated epithelioid sarcoma
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Adipocytic tumors
Lipoma:
They are the most common soft tissue tumor composed of entirely fat.
On doppler ultrasound- Well circumscribed hyperechoic or isoechoic soft tissue mass with minimal or no internal vascularity/ no posterior acoustic shadowing.
MRI- It follows the fat signal intensity on all MR sequences (Fig.
1 showing imaging appearance of subcutaneous lipoma and Fig.
3 showing intramuscular liopma).
It may show thin internal septations.
Presence of thick internal septations (> 2 mm),
associated solid component and enhancing regions raise the suspicion of liposarcoma.
Congenital infiltrating lipomatosis of face:
It is a disorder of unknown etiology and is characterized by invasion of mature adipocytes in to the soft tissues.
It resembles lipoma on both CT and MRI imaging but it is infiltrative and it can involve the muscles,
nerves or synovium.
Fig.
2 showing the imaging appearance of Congenital infiltrating lipomatosis of face.
Fibroblastic/ myofibroblastic tumor
Fibroma :
It is a painless slow growing tumor commonly seen in extremities.
Imaging appearance varies according to cellularity and myxoid change.
It has high recurrence rate.
Usually they are equal or low signal intensity to skeletal muscle on T1W and T2W sequences(1).
Contrast enhancement is variable.
It may show no/ mild/ marked contrast enhancement.
Fig.
4 showing fibroma with marked contrast enhancement.
Fibrosarcoma:
It is a malignant soft tissue tumor seen in elderly patients.
On CT,
the attenuation of mass is similar to that of skeletal muscle on NCCT as well as CECT (Fig.
5).
On MRI they appears hypointense on T1W and mixed signal intensity on T2W sequences.
They often show band like areas of hypointense signal on all sequences because of fibrotic component.
Fibrohistiocytic tumor
Giant cell tumor of tendon sheath : It is a slow growing benign tumor.
It can be localised or diffuse.
Al- Qattan classified in to type I and II.
Type I tumor present as single mass.
In type 2 tumor,
there will be 2 or more mass which are not joined together.
On ultrasound,
it is solid and is seen in relation to the tendons.
On color doppler,
it will show increased vascularity (Fig.
6).
On MRI,
it appears low signal intensity on both T1W and T2W sequences with characteristic blooming artifact on gradient echo sequences(2).
Vascular tumor
Hemangioma : It is of 2 types,
infantile and congenital.
Infantile hemangioma appears in first few weeks and gradually involutes over years.
Congenital hemangioma can be rapidly involuting,
non involuting and partially involuting.
Hemangiomas are solid soft tissue lesions which will show increased vascularity (Fig.
7) and show diffuse homogeneous contrast enhancement.
Other imaging features of hemangioma will be discussed below in the vascular anomalies section.
Peripheral nerve sheath tumors
Schwannoma : It accounts for 5% of all benign soft tissue tumor.
They are eccentric in relation to nerve.
It may show target sign,
Fascicular sign,
split fat sign,
Nerve entry and exit sign and thin T2 hyperintense rim sign.
It usually shows cystic changes.
Fig.8 and 9 showing the imaging appearance of schwannomas.
Tumor of uncertain differentiation
Myxoma : It is a benign tumor with no malignant potential.
On Ultrasound,
they are hypoechoic with internal echoes and posterior acoustic enhancement.
They frequently show bright rim sign which is rind of fatty tissue around intramuscular myxoma(3).
Multiple myxomas are seen in mazabraud syndrome.
Fig.
10 showing the imaging appearance of intramuscular myxoma.
Synovial sarcoma : It is a malignant tumor seen in young patients.
It usually presents as juxta articular mass.
calcification can be seen in 30% cases.
Extrinsic erosions seen in 11-20 % cases.
On ultrasound they are be well defined or infiltrative (aggressive) solid hypoechoic mass with increased vascularity (Fig.
11).
On MR,
it frequently show triple signal intensity sign on T2W sequence(4) (Fig.
12 and 16).
Undifferentiated/ unclassified sarcoma
Undifferentiated pleomorphic sarcoma : It is a highly grage tumor seen in elderly patients and has poor prognosis.
No specific imaging features are there for diagnosis.
They are heterogeneous solid mass which frequently shows cystic changes (Fig.
13 and 14).
on MR,
it usually present as large aggressive intramuscular mass which is heterogeneous on both T1 and T2W sequences (Fig.
14).
It can also show triple signal intensity sign on T2W sequences (Fig.
15).
Calcification can be seen in 30% cases.
Other malignant soft tissue lesions:
Malignant melanoma : Musculoskeletal involvement im melanoma can be due to contiguous extension/ hematogenous metastasis.
Metastatic melanoma can present as single or multiple subcutaneous nodules.
On MR,
hyperintense nodules on T1W sequences raise the suspicion of melanoma.
Fig.
17 showing imaging appearance of malignant melanoma.
Ewing sarcoma: It is the second most common malignant bone tumor in children.
Pain and swelling are the common clinical presentation.
They can present as large soft tissue mass.
Bone destruction and bone marrow involvement helpful in diagnosis.
it may also show triple signal intensity sign.
Fig.
18 showing Ewing sarcoma of right 4th toe presenting as soft tissue mass.
Non Hodgkin Lymphoma : Musculoskeletal involvement occurs as a part of disseminated disease.
Primary muscular lymphoma is very rare.
It can present as focal mass / diffuse muscle infiltration.
On ultrasound,
they are hypoechoic solid mass with or without underlying bone destruction.
On CT,
they are similar in attenuation to that of skeletal muscle with variable enhancement (Fig.
19).
vascular anomalies
They are classified in to vascular tumor and vascular malformations(5) (Fig.
20).
Hemangioma,
hemangioendothelioma,
kaposi sarcoma and angiosarcoma belongs to vascular tumor (Fig.
21).
Vascular malformations are classified in to simple,
combined,
those of major named vessels and those associated with other anomalies.
Approach and management of vascular anomalies is described in Fig.
22 & Fig.
23
Simple vascular malformations - Capillary,
venous,
lymphatic and AVM/ Arteriovenous fistula.
Hemangioma:
Most common vascular anomaly.
Infantile hemangioma usually appears in first few weeks of life and gradually involutes over years.
On gray scale ultrasound they are well defined solid soft tissue lesion with few discrete internal vessels.
On color doppler,
the vessels will show low resistance arterial waveforms.
On MRI they are solid mass with prominent flow voids.
No phleboliths seen.
It usually show early diffuse homogeneous enhancement (Fig.
25 & 26) and involuting lesions will show variable enhancement (Fig.
24).
They may show type 2 curve,
benign pattern of contrast enhancement (Fig.
27).
simple vascular malformations:
Venous malformation:
They are slow flow malformation and usually present as soft,
compressible ,
non pulsatile discrete lobular mass / abnormal dialted channels.
On gray scale ultrasound,
they show abnormal dilated vascular channels which are compressible and phleboliths.
On color doppler,
they show venous flow. On MRI they show dilated vascular channels.
Flow voids are not seen.
Fluid -fluid levels can be seen.
It also shows slow gradual contrast enhancement (Fig.
28-30).
Glomulovenous malformation/ Glomangioma: They presents as multiple painful clusters of abnormal enhancing dilated superficial vascular channels (Fig.
31).
Lymphatic malformation: They are slow flow simple vascular malformation.
It can be macrocystic/ microcystic.
Macrocystic malformation shows multiple cysts seperated by thin septa.
septa may show mild enhancement.
It may show fluid-fluid levels (Fig.
32 & 33).
Microcystic lesion usually present as solid lesion and show diffuse contrast enhancement (Fig.
34).
Tumor like lesions of soft tissue
Pigmented villonodular synovitis (PVNS): It is an uncommon benign neoplastic proliferative disease affecting synovium.
On ultrasound they are soild hypoechoic lesion with increased internal vascularity mimicking synovial sarcoma.
PVNS and synovial sarcoma can be easily differentiated on MR imaging.
PVNS usually present as large solid soft tissue tissue mass which is hypointense on T2W sequence and also shows blooming artifact on gradinet echo sequence (Fig.
35 and 36).
Muscle hernia: They are focal herniation of muscle through defect in fascial sheath.
It can be traumatic/ constitutional.
chronic leg pain and swelling are the major complaints.
Tibialis anterior muscle is the one which is frequently herniated.
Herniation of muscle is prominent in standing position and subsides in supine position (fig.
37).
Dynamic ultrasound plays an important role in diagnosing muscle hernia.
Dermoid cyst: They are lined by squamous epithelium with skin appendages such as sebaceous glands and hair follicles in its wall.
On ultrasound,
it appears as well circumscribed soft tissue lesion with posterior acoustic enhancement and no internal vascularity.
On CT,
the lesion show fat attenuation and it can cause bone remodelling (Fig.
38).
Epidermal inclusion cyst : It is ectodermal inclusion cyst lined by squamous epithelium.
On MR,
it follows the CSF/ water signal intensity on all sequences (Fig.
39).
Bakers cyst : It is fluid filled gastrocnemius- semimembranosus bursa.
Fluid within bakers cyst can communicate freely with knee joint.
It is often asymptomatic.
On US and MR,
Presence of posterior knee cyst which will communicating with fluid between semimembranosus tendon and medial head of gastrocnemius(6) (Fig.
40).
Ruptured bakers cyst: It can cause severe pain in leg mimicking Deep vein thrombosis.
The cyst fluid tracks in to the calf muscles and present as large anechoic/ hypoechoic collection on ultrasound (Fig.
41).
Soft tissue infections:
Cellulitis: Refers to acute inflammation of dermis and subcutaneous tissue.
On ultrasound ,
there is increased soft tissue thickening and echogeneicty with subcutaneous edema and increased internal vascularity (Fig.
42).
Deeper soft tissue involvement can be identified with MRI.
Soft tissue cysticercosis : Upper extermity is commonly involved in soft tissue cysticercosis.
On ultrasound,
it appears as well defined anechoic cystic lesion with echogenic scolex with or without surrounding abscess (Fig.
43).
On MRI,
it shows well defined cystic lesion which is hypointense on T1W and hyperintense on T2W with hypointense scolex.
It may show peripheral rim enhancement.
Musculoskeletal tuberculosis
Tuberculosis can affect joints,
muscle ,
tendon and synovium because of lymphohematogeneous dissemination and manifest as arthritis,
myositis,
synovitis and tenosynovitis.
Tuberculous tenosynovitis: It presents as thickening of tendon and synovium with fluid collection in the synovial sheath.
The thickened synovium and tendon is hypointense on T1W and intermediate to hypointense on T2W sequences with post contrast enhancement.
Multiple rice bodies can also be seen.
Fig.
44 and 45 showing imaging appearance of tuberculous synovitis and tenosynovitis.
Tuberculous arthritis : It will show uniform synovial thickening,
larger bone erosions and rim enhancement at the site of bone erosions(7).
Fig.
46 showing imaging appearance of tuberculous arthritis of left elbow joint.