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Differential Diagnosis

There are several other well-recognized causes of pathological soft tissue calcification. They may be summarized as follows:

1. Peritendinitis calcarea, especially around the shoulder or elbow.

2. Dystrophic calcification in dead or injured tissue, e.g., myositis ossificans, calcified tuberculous lymph nodes, calcified parasites, or other granulomas.

3. Metastatic calcification in endocrine or metabolic disorders, e.g., hypercalcemia, hyperphosphatemia. Such calcification is usually in the kidneys, in blood vessels, or around joints; very rarely, it occurs in the lungs, alimentary tract, or conjunctiva.

4. Calcinosis universalis or circumscripta: the calcium is in or under the skin, and is linear rather than tumorous.

5. Vascular calcification in arteries, veins, atheromatous plaques, and phleboliths.

6. Calcification in various soft tissue tumors, such as synoviomas and matrix-producing tumors.

7. Dermatomyositis, especially in juveniles, may show radiographic calcinosis in four common patterns: deep calcified masses, superficial calcified masses, and deep linear or diffuse subcutaneous deposits. These occur in up to 70% of patients, but rarely there is another pattern, "milk of calcium:' This is not easy to see on plain radiographs but has been demonstrated with ultrasonography and CT.

There are intermuscular fluid collections with echogenic particles on ultrasonography and heavy calcification with a linear pattern on CT. The fluid collections move freely when compressed. MRI will be normal with T 1-weighted images, but there will be increased signal response on T 2-weighted images. The clinical presentation and the mobile fluid permit differentiation from tumoral calcinosis.

The differential diagnosis of these groups of calcification is seldom difficult. Few will be mistaken for tumoral calcinosis. In the early stages, when the tumors are small, dystrophic calcification may be suspected. The most frequent error is to ascribe tumoral calcinosis to a "calcified bursa" or a "calcified lipoma" but once the entity of tumoral calcinosis is remembered, such errors are infrequent. There is little difficulty in excluding the various types of myositis ossificans: there is almost always a clear history of preceding trauma, and the calcifications are often linear rather than lobulated masses. Bone formation is a rare finding in tumoral calcinosis, has only been demonstrated histologically, and never recognized radiologically.

Calcification of necrotic granulomas, particularly calcified tuberculous lymph nodes, is common in the tropics, and must be differentiated from tumoral calcinosis (Fig. 29.14). In most patients, the anatomical site provides this distinction: the masses of tumoral calcinosis have not been reported in the neck or in the inguinal region. Tumoral calcinosis is frequent around the hip, but examination of the patient will distinguish tumoral calcinosis from calcification in inguinal and femoral lymph nodes or postsurgical or paralytic calcification. Tumoral calcinosis around the shoulder usually lies alongside the humeral head and adjacent to the scapula, but in the early stages might resemble tendon calcification or calcified axillary nodes. Clinical examination can be helpful. In the popliteal fossae distinction may be more difficult radiologically, but clinically a calcified granuloma is less mobile and less well defined than the small nodule of tumoral calcinosis. An erect view (or transverse horizontal projection) will often show fluid levels in some cases of tumoral calcinosis. No other ectopic calcified mass will ever show a fluid level. However, this may be difficult to demonstrate in small tumors or those with a solid or lacy pattern. The rim calcification of a hydatid cyst is usually smooth and most cysts are round, without any resemblance to tumoral calcinosis. When a hydatid cyst collapses, heals, and scars, the result is an amorphous mass, quite unlike the lobulated, septate appearance of tumoral calcinosis.

Fig. 29.14. Tuberculous debris around a healed tuberculous hip joint. The state of the joint and the clinical history will help to differentiate this calcification from tumoral calcinosis.

Calcification within parasites can usually be recognized by the shape and pattern of the calcified worm or may present as an amorphous mass: calcified parasites are often multiple and more superficial.

In the various types of metabolic calcification, such as occurs in hyperparathyroidism, chronic nephritis, vitamin D intoxication, and the milk-alkali syndrome, there are two distinguishing features: there is associated bone emineralization and in many cases there is visceral calcification. Neither occurs in tumoral calcinosis, although vascular calcification at an early age has been reported, perhaps due to hyperphosphatemia.

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