Imaging Diagnosis

Since wandering adult worms eventually die and calcify, plain radiographs (particularly of the extremities) may show thread-like calcification that may appear as a coiled, broken line (Fig.26.33). Hands and feet are especially common regions to find this whorled calcification. It has also been seen on mammograms (Fig. 26.34). These tiny thread-like or whorled soft tissue calcifications when seen in individuals from West or Central Africa, are characteristic features that permit the probable identification of Loa loa.

Parasitic, granulomatous, and almost any dystrophic calcification may look similar. However, there may be some distinguishing features. For example, small ovoid rim calcifications are seen in cysticercosis (Taenia solium); if calcifications are larger, hydatid cysts should perhaps be considered. Linear calcification suggests nematode infection. This includes filarial parasites and other nematode infections such as Dracunculus medinensis, subcutaneous dirofilariasis, Onchocerca volvulus, and larva migrans (Toxocara spp.). The wandering larvae of geohelminths in the aberrant human host are too small to be seen on plain films, except perhaps by mammography, where they would appear as punctate calcifications. Trichinella spiralis commonly calcifies when the encysted muscle larva is dead, but, again, it is too small to be seen on extremity radiography. It has been reported in the pectoral muscle on mammograms. The above features notwithstanding, knowledge of the geographic distribution of parasitic disease probably gives the most insight as to which parasite is likely to be the cause of radiographic calcification.

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Fig. 26.33 A-D. Loiasis. Four extremity radiographs from different patients showing thread-like and clustered, punctate calcification from nematodes that have died while migrating through the soft tissues (there are three worms in B and two in C). (A, B, D are from Nigeria; C is from Cameroon).

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Fig. 26.34A,B. Loiasis. Mammograms of a 40-year-old female who was evaluated for a right breast mass. Two types of calcification are seen: A spiral-shaped (arrow) and B rod-shaped (small arrow). The calcification morphology may be similar to that in Fig. 26.33 but is better visualized due to the higher resolution of mammography. (Courtesy of Dr. R. Novak).