Journal of Ultrasound in Medicine, Vol 10, Issue 2 83-87, Copyright © 1991 by American Institute of Ultrasound in Medicine
Sonographic diagnosis of premature cervical dilatation. Potential pitfall due to lower uterine segment contractions
J. P. Karis, B. S. Hertzberg and J. D. Bowie
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710.
Antenatal sonography is an accepted method of evaluating the cervix and
lower uterine segment. Dilatation of the endocervical canal can be missed
due to compression by an overdistended urinary bladder, intermittent
changes in configuration of the cervix, and suboptimal visualization.
However, the potential for overdiagnosis of this entity has not been
previously emphasized. We present 14 cases demonstrating how contractions
in the lower uterine segment can result in an appearance that falsely
simulates preterm dilatation of the endocervical canal. The overdiagnosis
of this entity can be avoided by distinguishing the following features
typical of "pseudodilatation" due to a contraction: (1) apparent cervical
length greater than 5 cm; (2) demonstration of normal-appearing cervical
tissue distal to the apparently dilated region; and (3) rounding of the
myometrium surrounding the apparently dilated area. If any of these
features is detected in a patient with sonographic characteristics
suggesting dilatation of the cervix, the possibility of pseudodilatation
should be considered, and the lower uterine segment should be rescanned
later in the examination.
