Comparison of Transabdominal, Transvaginal, and Transrectal Ultrasound Examinations of Seven Female Western Lowland Gorillas (Gorilla gorilla gorilla)
Ultrasonographic reproductive examinations were conducted in conjunction with immobilizations for translocation of seven female western lowland gorillas (Gorilla gorilla gorilla). At the time of examinations, gorillas were 9-36 yr of age and 70-128 kg. All had previously been pregnant one to nine times. Most pregnancies resulted in term deliveries, but a few ended in spontaneous abortions.
Reproductive tract ultrasound (Impact VFI, Ausonics, General Electric Co, San Jose, CA 95112 USA) imaging was conducted by transabdominal, transvaginal, and transrectal scans. Transabdominal scanning was performed with a variable frequency (5.0 or 7.5 mHz) microconvex linear array ultrasound probe. Transvaginal and transrectal scanning was performed with a 6.0 mHz transvaginal ultrasound probe. Obesity and abundant gastrointestinal gas or ingesta limited transabdominal imaging. The short muscular vagina with limited distensibility restricted mobility of the ultrasound probe and limited transvaginal scanning. In addition, the axial orientation of the uterus and cervix1 precluded perpendicular acoustic imaging with a consequent compromise in image quality.
The highest quality and most reliable images of the female gorilla reproductive tract were achieved with transrectal ultrasonography. The large distensible rectal lumen and proximity to the reproductive tract allowed manipulation of the probe to attain a sonic footprint perpendicular to the reproductive tract. This optimized the resulting images of the vagina, cervix, uterus, and ovaries. A Nabothian cyst of the cervix was identified in one gorilla. Uterine findings included normal trilaminar preovulatory endometrium, early proliferative endometrium, secretory endometrium, and a probable myoma. The stage of the menstrual cycle was accurately determined in all females except the latter; in that case the acoustic shadow of the mass limited uterine imaging. Ovaries could not be imaged in all females, but at least one ovary was visualized in five of the seven. The two gorillas whose ovaries were not visualized included one that developed anovulatory infertility after an abortion, and the gorilla with the uterine mass. Ovarian findings included inactive and normal ovaries, ovarian follicles, and corpora lutea.
Ultrasound imaging of the human female reproductive tract is typically conducted by a transabdominal or transvaginal approach, although it is recommended that virgins or elderly women with introital stenosis be imaged transrectally.2 Due to the close taxonomic relationship of human and gorilla, techniques used for humans are commonly applied to the gorilla. As a result of differences between the human and gorilla gastrointestinal and reproductive anatomy, and improvement in ultrasound imaging by an acoustic footprint perpendicular to the area of interest, we recommend that transrectal ultrasound imaging be used to optimize imaging of the female gorilla reproductive tract.
The authors thank the WCS Department of Mammalogy and the WCS Hospital Assistants and Veterinary Technicians for their assistance with the procedures.
1. Atkinson WB, H Eftman. 1950. Female reproductive system of the gorilla. In: Gregory, W. K. (ed). The anatomy of the gorilla. Columbia University Press, NY, N.Y., Pp. 205-212.
2. Goldstein SR, IE Timor-Tritsch. 1995. Ultrasound in Gynecology. Churchill Livingstone, New York, NY.