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Soft Tissue Imaging


Localized Calcification and Ossification

Localized Calcification and Ossification

Definition

Deposition of calcium pyrophosphate dihydrate or calcium hydroxyapatite within soft tissues is called mineralization or calcification

  • Metastatic: the result of abnormal calcium metabolism

  • Calcinosis: occurring with a normal calcium metabolism

  • Dystrophic: related to tissue damage

  • Ossification: bony trabeculae are discernible (either ectopic or heterotropic) ▸ calcium deposits tend to be more densely sclerotic than in normal bone

  • The differential diagnosis is divided into:

    • ■

      Generalized calcification (see separate section)

    • ■

      Localized calcification

    • ■

      Ossification

Localized Calcification – Trauma

Definition

Any cause of focal soft tissue necrosis (e.g. injection sites, radiation damage, thermal injuries) can predispose to calcification

  • Blunt trauma can cause fat necrosis within the subcutaneous tissues and areas of dystrophic calcification

    • ■

      Any haematoma (particularly subperiosteal) may calcify

  • Calcific myonecrosis: calcification of atrophic muscles occurring 1–2 months after a severe crush injury

Localized Calcification – Tumours

Definition

Widespread soft tissue calcification is a rare manifestation of disseminated malignancy where there is hypercalcaemia associated with extensive bone destruction (e.g. metastases, leukaemia and myeloma)

  • Localized intratumoral calcification may occur within any soft tissue tumour due to haemorrhage or necrosis

  • Benign mineralizing tumours: soft tissue chondroma (punctuate or ‘ring and arc’ calcification) ▸ lipoma (ossification can occur, especially if it is parosteal) ▸ haemangiomas (phleboliths)

  • Malignant mineralizing tumours: extraskeletal osteosarcoma ▸ extraskeletal chondrosarcoma ▸ synovial sarcoma (with a central rather than peripheral distribution)

Heterotopic Ossification

Definition

This follows inappropriate differentiation of fibroblasts into osteoblasts in response to local inflammation

  • Developmental causes include fibrodysplasia ossificans progressiva, melorheostosis and progressive osseous heteroplasia

  • Post-surgical: this particularly occurs following a total hip arthroplasty (± pain and restricted movement)

  • Post-traumatic:

    • ■

      Pellegrini–Stieda lesion: ossification of the medial collateral knee ligament

    • ■

      Neurogenic heterotropic ossification: soft tissue ossification associated with CNS injuries (with prolonged unconsciousness and spinal trauma) ▸ there is a periarticular distribution (commonly affecting the hips) ▸ surgery is associated with recurrence

    • ■

      Avulsion of an ossification centre: in the skeletally immature an avulsed ossification centre may continue to grow ▸ this may present later as a large ossified soft tissue mass (commonly affecting the pelvic and hamstring pelvic origins)

Myositis Ossificans

Definition

Heterotopic bone formation within muscles, tendons and fascia following trauma ▸ it is possibly due to haematoma ossification or displacement of periosteal elements into the soft tissues

  • Haemorrhage is followed by mineralization ▸ this is first seen in the periphery with a gradual reduction in the size of the mass (which are both helpful in distinguishing from a mineralizing soft tissue sarcoma)

  • Early biopsy should be avoided (as it can resemble a soft tissue osteosarcoma)

  • It is associated with burns and paraplegia ▸ it is commonly seen around the elbow and in the thigh

Angiography

A hypervascular lesion

Scintigraphy

Increased activity

MRI

T2WI/STIR: florid perilesional oedema involving the whole affected muscle compartment

  • Pseudomalignant myositis ossificans: this is similar radiographically and pathologically to myositis ossificans (but there is no history of trauma)

Antecubital myositis ossificans. (A) The plain XR shows the characteristic peripheral ossification and multiple high SI fluid levels (haemorrhage) on the axial MR image (B). †

Synovial sarcoma. Axial CT demonstrating a soft tissue mass lateral and posterior to the femur containing calcifications. *

Myositis ossificans associated with paraplegia. Very extensive ossification is seen around both hips. †

Pellegrini–Stieda lesion of the medial femoral condyle. †

Calcified liposarcoma. †

Ischial avulsion. (A) XR at presentation shows the avulsed ischial apophysis. (B) Three years later the apophysis has continued to grow to form a large ossified mass. *

Cavernous haemangioma with multiple phleboliths. †

Generalized Soft Tissue Calcification

Metabolic Disorders

  • This results from prolonged elevation of the serum calcium (or more importantly serum phosphate) ▸ many causes, but chronic renal failure is the most common

  • Primary hyperparathyroidism : calcification is typically seen involving arteries, cartilage (chondrocalcinosis), and periarticular tissues

  • Secondary hyperparathyroidism : soft tissue and vascular calcification is more common than in primary disease ▸ chondrocalcinosis is infrequent

  • Hypoparathyroidism : predominantly subcutaneous calcification (also with basal ganglia calcification) ▸ osteoslerosis ▸ premature epiphyseal closure ▸ band-like paraspinal calcification (mimicking DISH)

  • Pseudohypoparathyroidism : there are similar features to hypoparathyroidism but it is associated with growth deformities (rounded facies, broad bones, cone epiphyses, short metacarpals and metatarsals – especially the 1 st , 4 th and 5 th )

  • Pseudopseudohypoparathyroidism: XR features are identical to pseudohypoparathyrodism (but with a normal serum calcium and phosphate)

  • Hypervitaminosis D: smooth lobulated amorphous calcium hydroxyapatite masses within the periarticular regions, bursae, tendon sheaths and the joint capsule ▸ dense metaphyseal bands and cortical thickening (± osteosclerosis) in children ▸ most of these features are absent in adults (osteosclerosis may be the only manifestation)

Arterial Calcification

  • Monkeberg's arteriosclerosis: finer ‘pipe-stem’ calcification seen with medial degeneration

  • Diabetes: calcification of the small vessels of the feet

  • Renal failure/hyperparathyroidism : a fine more generalized pattern of arterial calcification

  • Aneurysms : rounded, curvilinear and crescentic calcification

Venous Calcification

  • Phleboliths: these are common and represent a calcified venous thrombus (leading to a small circular calcified density) ▸ they are often seen within pelvic veins ▸ they are also seen in chronic varicosities and cavernous haemangiomas

  • Maffucci's syndrome : multiple phleboliths (haemangiomas) and enchondromas

  • Venous incompetence : subcutaneous calcification and organized periosteal new bone formation

  • Pearl Venous mural calcification is rare

Bacterial Infection

  • Dystrophic calcification may occur within resolving abscesses (e.g. spine TB)

  • Extensive calcified lymphadenitis: old TB infection ▸ histoplasmosis ▸ coccidioidomycosis

  • Leprosy is a rare cause of nerve calcification

Parasitic Infection

  • Echinococcosis (hydatid): liver and lung calcifications

  • Schistosomiasis : urinary tract calcifications

  • Cystercicosis (pork tapeworm: Taenia solium): larvae show a predilection for muscle, subcutaneous tissues and the brain ▸ calcified dead cysts are oval with a lucent centre and are orientated in the direction of the muscle fibres

Fibrodysplasia Ossificans Progressiva (Myositis Ossificans Progressiva)

Definition

A congenital connective tissue disorder with an autosomal inheritance and variable penetrance ▸ it is unrelated to myositis ossificans

Clinical presentation

There is progressive swelling and ossification of the fascia, aponeuroses, ligaments, tendons and skeletal muscle connective tissues

  • It usually affects the neck and shoulder girdle first (before the onset of multifocal calcification which ultimately progresses to ossification)

Radiological features

Progressive ossification produces large masses that can bridge bones (and can also cause respiratory compromise within the thorax)

  • Associated skeletal abnormalities : short 1 st metacarpals and metatarsals ▸ small cervical vertebral bodies with relative prominence of the pedicles

Connective Tissue Disorders (Acquired)

  • Crystal deposition diseases

  • Dermatomyositis

  • Scleroderma (progressive systemic sclerosis)

  • Calcium pyrophosphate dehydrate deposition disease (CPPD)

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