Case #193 – December, 2006

A 45-year-old woman had a nodule approximately 1 cm in diameter located near a scar from a previous mastectomy. The patient had traveled to several western and central European countries within the past year. The nodule was removed and tissue sections were stained with hematoxylin and eosin (H & E). Figures A-D show what was seen in the tissue sections. Figure A was taken at 50×, B at 100×, and Figures C and D at 400× magnification respectively. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

This was a case of dirofilariasis caused by Dirofilaria, likely D. repens based on the geographic location and travel history of the patient. The normal host for D. repens is dogs. Diagnostic features were:

a thick, multi-layered cuticle (Figure C, green bracket) with longitudinal ridges (Figure D, green arrow).
a prominent internal lateral ridge and large lateral chords (Figure C, black and blue arrows respectively).
well-developed, polymyarian muscle cells (Figures C and D, yellow bracket).
Lack of paired uterine tubes indicates that this was probably a male worm.

Figure C

Figure D