Central Nervous System

Amebic abscesses may rarely occur within the brain or spinal cord and even more rarely may be the first evidence of the infection (Fig.1.10). The clinical (and radiological) findings cannot be differentiated from cerebral or spinal abscesses of any other etiology. There may be some confusion (particularly when referring to the literature) because meningoencephalitis can be caused by other amebae. These are the free living amebae, Naegleria fowleri and Acanthameba astronyxys, which can be found in mud around fresh water ponds and swimming holes. Human infection with E. polecki (normally a parasite in pigs and monkeys) has rarely been reported, is difficult to distinguish from E. histolytica, and is almost never symptomatic.

Skin

Although of less concern to radiologists, cutaneous amebiasis presents diagnostic pitfalls for both the clinician and pathologist. Cutaneous amebiasis may involve anus, genital skin, vagina and cervix, as a consequence of contiguous spread from colon and rectum. Amebiasis of the penis may develop after rectal intercourse. Amebic ulcers of the trunk (Fig. 1.11A,B) are usually complications of penetrating amebic lesions of the colon, liver, pleura, peritoneum, or pericardium; and are painful, tender, and malodorous. That amebiasis can involve skin must be kept in mind especially by those practicing in regions where amebiasis is common. The hyperplastic, cauliflower-like appearance of peri-anal, perineal, and genital amebiasis can be easily confused clinically with squamous carcinoma or a mycosis (Fig. 1.11C,D).

Amebiasis versus Carcinoma

Amebiasis may mimic carcinoma, not only in the colon and rectum where "napkin ring" or "apple core" constrictions can be caused by amebomas, but especially in skin and mucous membranes. Amebiasis of the anus, perineum, penis, and vulva may mimic carcinomas so strikingly that radical excisions have been done on the basis of clinical appearance alone. Amebiasis of the uterine cervix, by causing induration, swelling and ulceration, may also be mistaken for carcinoma. Thus, benign amebic lesions may be inadvertently excised when anti-amebic therapy alone is indicated. Further complicating this diagnostic hazard is the fact that carcinomas may be colonized by E. histolytica. A patient with an amebic lesion resembling a carcinoma must therefore be rebiopsied if there is any suspicion of underlying malignancy.