SOFT TISSUES

Question 1

LINEAR AND CURVILINEAR SOFT

TISSUE CALCIFICATION

Answer 1

Common causes
1. Arterial—i.e. atherosclerosis. If seen in the hands or feet, this
suggests underlying diabetes or hyperparathyroidism (secondary >
primary). Calcification can also be seen in aneurysms (e.g. popliteal).

2. Cartilage—i.e. chondrocalcinosis; suggests CPPD.
3. Ligament/tendon.
   (a) Calcific tendonitis—i.e. hydroxyapatite deposition disease (HADD). Commonly involves supraspinatus and gluteus medius tendons.
   (b) Seronegative spondyloarthropathy—entheseal calcification.
   (c) Alkaptonuria*—rare.
   (d) Fluorosis—rare.

Less common causes

4. Neural—characteristic of leprosy.
5. Parasites

Question 2

SOFT TISSUE CALCIFICATION

Answer 2

Common causes
1. Dystrophic calcification—calcification in abnormal tissue in the presence of normal calcium metabolism.

(a) Previous trauma.
(i) Injection granuloma—typically in gluteal region.
(ii) Haematoma.
(iii) Calcific myonecrosis—may occur without history of trauma, especially in diabetics. Amorphous calcification.
(iv) Burn injury.

(b) Connective tissue disease.
(i) Systemic sclerosis—nodular, periarticular or subcutaneous calcification especially in the hands.
(ii) Dermatomyositis/polymyositis—typically bilateral and symmetrical sheet-like calcification in skin and muscles, most common around the hips and in the thighs.
(iii) SLE—can be nodular or sheet-like.
(iv) Mixed connective tissue disease—nodular or sheet-like.
(v) Ehlers-Danlos syndrome—nodular subcutaneous
calcification over bony prominences.
(vi) Pseudoxanthoma elasticum.

(c) Arthropathy.
(i) Tophi—gout; also rarely CPPD.
(ii) Rheumatoid nodules—may calcify.

(d) Venous (phleboliths)—oval with lucent centre, associated with venous insufficiency (± lacy subcutaneouscalcification), but also seen in soft tissue haemangiomas. A deep vein thrombosis (DVT) may also calcify.

Less common causes
2. ‘Metastatic’ calcification—calcification in normal tissues in the presence of abnormal calcium metabolism. May be the result of chronic hypercalcaemia from any cause, particularly in dialysis patients. It has an identical appearance to tumoural calcinosis, but other features of secondary hyperparathyroidism are often present.

3. Tumoural calcinosis—rare, autosomal dominant, usually in
   Afro-Caribbeans. Well-defined lobulated calcified masses occur on
   the extensor surfaces of large joints. Internal fluid levels, if present,
   are highly suggestive (also seen in metastatic calcification).
4. Neoplasia.
   (a) Benign.
   (i) Haemangioma—multiple clustered phleboliths in an unusual distribution.
   (ii) Chondroma—chondroid calcification, often periarticular.
   (iii) Nerve sheath tumours—e.g. ancient schwannoma.
   (iv) Pilomatricoma—most common in the head or neck of children and adolescents. Benign tumour of the hair follicle, so located at the deep margin of the dermis.
   (b) Malignant—most sarcomas can contain calcification; the commonest are:
   (i) Synovial sarcoma—typically found in young adults in the lower limb close to a joint (especially the knee). 30% contain calcification.
   (ii) Liposarcoma—may contain variable amounts of dystrophic calcification.
   (iii) Chondrosarcoma—chondroid calcification. Can mimic chondroma but usually larger + adjacent bone erosion

Question 3

SOFT TISSUE OSSIFICATION 4

Answer 3

1. Trauma.
   (a) Myositis ossificans—posttraumatic soft tissue ossification (usually intramuscular) that evolves over weeks to months. Starts as an ill-defined osteoid matrix, which matures to bone with a dense periphery and a less dense centre. In the early stage this can mimic an aggressive lesion on plain film or MRI—follow-up imaging may be required.
   (b) Postsurgical—especially after hip replacement.
2. Paralysis—usually around large joints.
3. Parosteal osteosarcoma—arises from the outer periosteum. May mimic myositis ossificans, except density is highest centrally rather than peripherally. Extraskeletal osteosarcomas (arising within soft tissues) can also rarely occur.
4. Fibrodysplasia ossificans progressiva—hereditary; progressive
   mature ossification of muscles, ligaments and tendons.
   Sternocleidomastoid is often the first site of involvement

Question 4

SOFT TISSUE MASSES

T1 hyperintense

Answer 4

1. Mass containing fat

(a) Lipomatous tumours.
(i) Lipoma—benign, very common. Composed of pure fat with no solid elements apart from thin septa. The signal suppresses completely on fat-sat sequences. Usually subcutaneous in location, but can occur
anywhere. Beware of lipomas deep to the subcutaneous fascia—biopsy is often required to exclude a welldifferentiated liposarcoma, especially in the mediastinum or retroperitoneum (lipomas are rare here).
(ii) Atypical lipomatous tumour/well-differentiated liposarcoma—predominantly fatty mass containing thick septa or small nonfatty nodules (<1 cm).
(iii) Dedifferentiated liposarcoma—fatty mass with a large
nonfatty nodular component (>1 cm) representing an area of dedifferentiation.
(iv) Myxoid liposarcoma—often contains little fat. T2 bright, mimicking a cyst
(v) Pleomorphic liposarcoma—high grade; usually contains minimal fat, mimicking other sarcomas.
(vi) Lipoma variants—e.g. lipoblastoma (young children only), angiolipoma, myolipoma, spindle cell lipoma, chondroid lipoma. These are benign but contain enhancing solid elements, mimicking liposarcoma.

(b) Fat necrosis—subcutaneous fatty lesion + a thick hypointense
capsule ± calcification. Most common in the gluteal region.

(c) Haemangioma—contains streaky or lace-like areas of fat ±hypointense phleboliths.
(d) Elastofibroma—classic location between the scapula and ribcage. Contains fibrous tissue and streaks of fat; may mimic the striated appearance of skeletal muscle.
(e) Hibernoma—benign tumour of brown fat. T1 signal is usually not as high as normal fat. Well-defined, usually contains prominent feeding vessels (unlike liposarcoma), and often enhances avidly. High uptake on PET.
(f) Lipomatosis of nerve—diffuse fatty infiltration along nerve fibres; most common in the median nerve. May be associated with macrodactyly (localised gigantism of one or more digits) due to overgrowth of fat and bone.
(g) Myositis ossificans—when mature, contains fatty marrow elements.
2. Mass containing haemorrhage—e.g. subacute haematoma (no enhancement), haemorrhagic tumour (usually has enhancing components).
3. Mass containing proteinaceous fluid—e.g. ganglion, abscess, chronic seroma.
4. Melanoma—including melanoma metastases

Question 5

ST MASSES

T2 hypointense

Answer 5

1. Fibrotic mass.
   (a) Fibroma of tendon sheath—typically found on tendons in the hand or wrist. Small T2 hypointense nodule, variable enhancement.
   (b) Nodular fasciitis—usually <4 cm, attached to subcutaneous or muscle fascia. Early lesions are cellular and T2 hyperintense, more mature lesions are collagenous and T2 hypointense. Usually shows diffuse enhancement. Tender and rapidly growing; can be well- or ill-defined. Most common benign lesion mistaken for sarcoma.
   (c) Desmoid tumour—usually painless (unlike nodular fasciitis).
   Typically very infiltrative (more so than sarcomas), with variable diffuse enhancement and no internal necrosis or haemorrhage (unlike sarcomas). Can be T2 hyperintense (early and cellular), hypointense (mature and collagenous) or mixed.
   Occurs in three locations:
   (i) Anterior abdominal wall—commonest tumour of the abdominal wall, typically associated with pregnancy. Often occurs at caesarean-section scar.
   (ii) Intraabdominal—usually in the mesentery but can be retroperitoneal or pelvic. Often associated with Gardner syndrome.
   (iii) Intramuscular—e.g. shoulder and hip girdles, chest wall, back, neck. Can be sporadic or associated with Gardner syndrome (especially if multiple).
   (d) Elastofibroma—may be mainly fibrotic with minimal fat.
   (e) Fibrosarcoma—lobulated mass with heterogeneous signal and
   enhancement ± areas of necrosis or haemorrhage. Can contain
   T2 hypointense bands of collagen.
2. Mass containing calcium—any cause of soft tissue calcification or
   ossification.
3. Mass containing haemosiderin.
   (a) Endometrioma—especially in caesarean-section scar. Can
   mimic desmoid tumour.
   (b) Giant cell tumour of tendon sheath—extraarticular
   form of pigmented villonodular synovitis (NB: can also
   occur in bursae). May mimic fibroma of the tendon
   sheath, but demonstrates blooming on gradient echo
   sequences.
4. Mass containing flow voids—e.g. aneurysm, AVM.
5. Mass containing gas—e.g. abscess.

Question 6

ST MASSES

Homogenously T2 bright (cyst-like)

Answer 6

No enhancement/rim enhancement only post IV gadolinium
1. Degenerative/idiopathic—e.g. epidermal inclusion cyst (aka
sebaceous cyst, attached to dermis), ganglion cyst (associated
with a joint, especially the wrist), bursa (e.g. iliopsoas bursa
and many others), paralabral cyst (shoulder/hip), meniscal
cyst (knee).
2. Traumatic—e.g. haematoma, seroma, lymphocele (related to
lymphadenectomy) or Morel-Lavallée lesion (subcutaneous
shearing injury resulting in a fluid collection ± fat globules,
typically located over the greater trochanter, knee or scapula).
3. Abscess—usually has thick, irregular rim enhancement with
surrounding oedema (except tuberculous ‘cold’ abscess).
4. Lymphangioma—multiloculated, often traverses compartments.
Usually presents in childhood.
5. Cysticercosis*—small intramuscular cyst + hypointense scolex;
often multiple.
6. Hydatid cyst—rare in soft tissues.

Internal enhancement post IV gadolinium
1. Peripheral nerve sheath tumour—arises from nerve, either
eccentric (schwannoma) or central/fusiform (neurofibroma). A
peripheral rim of fat (split fat sign) is typical. Can occasionally be
homogenously T2 bright without the characteristic central
hypointensity (target sign). Large schwannomas can undergo
cystic degeneration.
2. Haemangioma—T2 bright + streaks of fat ± hypointense
phleboliths. Usually shows avid or delayed internal enhancement
depending on speed of internal blood flow.
3. Glomus tumour—characteristic location under nailbed. Enhances
avidly.
4. Myxoma—benign, typically intramuscular + a thin rim of fat.
Mimics a cyst on T1/T2, but usually shows mild to moderate
internal enhancement. Flame-shaped oedema is often seen
extending along the muscle fibres at the poles of the mass.
5. Myxoid sarcomas—e.g. myxofibrosarcoma (older adults),
fibromyxoid sarcoma (young adults), myxoid liposarcoma (small
foci of fat), extraskeletal myxoid chondrosarcoma. Can mimic
myxoma but often more heterogeneous with no rim of fat.
6. Synovial sarcoma—can be well-defined and homogenously T2
bright when small, mimicking a benign lesion, but usually shows
avid enhancement and may contain hypointense calcification,
haemorrhage or fluid-fluid levels.
7. Other necrotic/cystic malignancies—e.g. undifferentiated
pleomorphic sarcoma, cystic or mucinous metastases.
8. Hidradenoma—arises from the dermis (sweat glands), usually
benign. Often contains enhancing nodular components.