Applied Radiology

Prepared by Osbert Egiebor, MD; Calvin Flowers, MD; Bradley Langer, MD, Department of Radiology, Cook County Hospital, Chicago, IL.

CASE SUMMARY:

A 44-year-old male presented with left chest discomfort following a motor vehicle accident. His past medical history was unremarkable, but his social history was significant for ingestion of inadequately cooked snakes prior to emigration to the U.S. from Africa 5 years before presentation. Physical examination was unremarkable except for mild tenderness over the posterior left fifth and sixth ribs. Hematologic profile and liver function tests were normal. Radiographs of the chest and ribs were obtained by the primary physician; an oblique radiograph of the lower chest and upper abdomen is shown (figure 1). Due to these findings, non-enhanced chest and abdominal CT images were obtained. What is your diagnosis?

DIAGNOSIS:

Pentastomiasis.

IMAGING FINDINGS:

The oblique radiograph in figure 1 shows multiple ring-like and cresentic calcific densities measuring 3 to 6 mm in size in both hemithoraces and the upper abdomen. The differential diagnosis at this time included cysticerci calcifications (usually oval with lucent centers, arranged in the direction of muscle fibers), granulomas, daughter cysts of hydatid disease (usually ring-like calcifications), guinea worm calcification with an irregular coiled appearance, and the thread-like calcifications of loa loa. Non-enhanced computed tomography (CT) of the chest and abdomen (figures 2,3) demonstrated the extensive ring-like and cresentic calcifications involving the following: both lungs, the pleural and pericardial surfaces, the liver, mesentery, omentum, the walls of the stomach, and the small and large bowels. The patient was discharged and prescribed a pain killer for possible musculoskeletal strain. His symptoms subsequently resolved.

DISCUSSION:

Pentastomiasis caused by Armillifer infestation is uncommon in developed countries. Armillifer armillatus usually infest the lungs of snakes such as vipers, pythons, and boa constrictors. The three species of Armillifer important to humans include A. armillatus, restricted to West Africa; A. moniliformis, seen in the Far East ; and Linguatula serrata, typically found in the Western hemisphere. Pentastomiasis, which presents classically with ring-like or cresentic soft-tissue calcifications due to calcified porocephalida nymphs, is the most frequent cause of chest and abdominal calcifications in endemic areas. ³ Humans get infected after ingesting inadequately cooked snake, or food and drink contaminated by the saliva of snakes containing the eggs of Armillifer . ³ The detailed life-cycle of the
parasite in humans is not well known, but the Armillifer nymphs have been found to cause significant disease because of the worm burden, location, and tissue migration. ⁵ The nymphs usually are found in the subpleural and subperitoneal spaces, the bowel walls, mesentery, and liver, resulting in a severe granulomatous reaction due to host response. The sixth molt of the nymph assumes a cresentic configuration in a fibrous capsule which later dies and undergoes dystrophic calcification.

Armillifer infestation usually is asymptomatic and is found incidentally at radiological evaluations, surgeries, and autopsies. ⁴ The calcified nymphs are characteristically seen on radiographs as multiple calcific densities which appear cresentic or linear en face and ring-like in profile. These densities range from 3 to 8 mm in size and have no particular alignment (figures 1-4). On CT the calcified nymphs approximate the density of bone, with significant streak artifacts which may simulate metallic foreign bodies (figures 3A,3B). The highest concentration of the calcified nymphs is in the upper abdomen due to extensive hepatic involvement. The highest incidence of Armillifer infestation on plain radiographs is reported from Ibadan, Nigeria, where 2% of adult males, 4% of adult females, and 1.4% of the general population are affected. ^1,2 This report is the first to document the CT features of pentastomiasis and we would expect the incidence to be higher on CT because it is more sensitive for the detection of calcification compared to plain radiographs. The infestation incidence at autopsy can be as high as 45%, as seen in Malaysian aborigines. ⁶ Although the parasitic infestation is commonly asymptomatic, it may cause nodules in the lungs and the submucosal lining of the stomach and jejunum mimicking tumors. ³ There is an association with a higher incidence of neoplasms, ¹ obstructive jaundice ⁷ and intestinal obstruction by fibrous bands. ⁸

CONCLUSION:

When confronted with the chest or abdominal x-ray of a patient with ring-like and cresentic calcifications from an endermic area, and a history of ingestion of snakes or food and drink contaminated by snakes' saliva, the possibility of pentastomiasis should be considered.