PEDIATRICS Vol. 106 No. 4 October 2000, pp. 844-848
EXPERIENCE AND REASON:
Isolated Large Third-Trimester Intracranial Cyst on
Fetal Ultrasound: Fact or Fiction?
Received Dec 21, 1999; accepted May 3, 2000.
* Neonatology Divisions of Pediatric Departments
Franciscan Skemp Healthcare
Mayo Health System
La Crosse, WI 54601
Departments of § Radiology, Neurology Division of Pediatrics,
and ¶ Neurosurgery
Franciscan Skemp Healthcare
Mayo Health System
La Crosse, WI 54601
Objective. To distinguish the fact from artifact of an isolated, large, intracranial cyst on prenatal sonography (PSG).
Background. The use of PSG is rapidly increasing with most obstetric ultrasounds occurring in general community settings like small hospitals and clinics with personnel who have variable training, experience, and interest levels. In contrast, most PSG articles and books are produced in large subspecialty centers with concentrated referral bases plus both highly-trained and experienced personnel.
Design/Methods. We report a series of 2 normal newborn patients who had a large prenatal unilateral intracranial cyst diagnosed by PSG in the 10 years between July of 1989 and 1999 at a rural community hospital. The newborns had imaging studies at birth and their neurodevelopmental progress was followed for several years. Textbook, bibliography and computerized Medline (1966-present) searches including prenatal ultrasound, observer variation, diagnostic errors, reproducibility of results, sensitivity and specificity, accuracy, central nervous system, false-positive, prenatal diagnosis, and brain were examined starting in August 1996 for reports.
Results. There were 4079 obstetric ultrasounds performed in 3.5 years, January 1996 through July 1999 at this rural community facility. This rate extrapolates to a total of 11 654 obstetric ultrasounds over the 10-year study period in which the 2 cases of intracranial cyst artifact occurred. Thus, the incidence of 2 intracranial cyst artifacts was estimated as 2/11 654 PSG, a .0002% false-positive rate.
Conclusions. This is the first report of the occurrence of
PSG artifacts in a community facility. Artifact is a real problem and
needs to be specified in differential diagnoses. There are ways to
decrease sonographic artifact
or at least to recognize itso our
estimates at a community hospital for its occurrence are presented with the relevant technical and ethical issues. None of these issues have
been previously reported in the pediatric literature. Our false-positive rate for large intracranial cyst compares favorably
with other reports. Our estimate may inflate our denominator by
reporting scans rather than the number of fetuses scanned, and our
numerator may miss cases that moved from the community. Confusion differentiating PSG artifact from reality often occurs when
interpreting static or frozen real-time images. The signs that sonogram
images may be artifacts include defects that: extend outside the fetal
body; change shape, size and echogenecity with different scan planes;
are not seen on all examinations; and are isolated in an otherwise
normal fetus. Failure to offer quality PSG in clinical settings where
it is available restricts access of pregnant women to the diagnosis of
fetal anomalies, and therefore restricts access to the options of
pregnancy termination, fetal therapy like fetal surgery, and delivery
options of timing, setting, and mode.We suggest a multidisciplinary approach to prenatal abnormalities like
isolated third trimester unilateral intracranial cyst in both primary
and tertiary care settings aids interpretation followed by expectant
conservative management without elaborate, risky, or terminal
interventions.
Key words:
prenatal ultrasound,
brain,
quality,
fetal
termination,
ethics.
