Isolated large third-trimester intracranial cyst on fetal ultrasound: Factor fiction?

Objective. To distinguish the fact from artifact of an isolated, large, int racranial cyst on prenatal sonography (PSG). Background. The use of PSG is rapidly increasing with most obstetric ultras ounds occurring in general community settings like small hospitals and clin ics with personnel who have variable training, experience, and interest lev els. In contrast, most PSG articles and books are produced in large subspec ialty 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 l arge 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 foll owed for several years. Textbook, bibliography and computerized Medline (1966-present) searches inc luding prenatal ultrasound, observer variation, diagnostic errors, reproduc ibility of results, sensitivity and specificity, accuracy, central nervous system, false-positive, prenatal diagnosis, and brain were examined startin g in August 1996 for reports. Results. There were 4079 obstetric ultrasounds performed in 3.5 years, Janu ary 1996 through July 1999 at this rural community facility. This rate extr apolates 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, t he 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 it-so our estimates at a community hospital for i ts occurrence are presented with the relevant technical and ethical issues. None of these issues have been previously reported in the pediatric litera ture. 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 case s that moved from the community. Confusion differentiating PSG artifact from reality often occurs when inter preting static or frozen real-time images. The signs that sonogram images m ay be artifacts include defects that: extend outside the fetal body; change shape, size and echogenecity with different scan planes; are not seen on a ll examinations; and are isolated in an otherwise normal fetus. Failure to offer quality PSG in clinical settings where it is available restricts acce ss of pregnant women to the diagnosis of fetal anomalies, and therefore res tricts access to the options of pregnancy termination, fetal therapy like f etal surgery, and delivery options of timing, setting, and mode. We suggest a multidisciplinary approach to prenatal abnormalities like isol ated third trimester unilateral intracranial cyst in both primary and terti ary care settings aids interpretation followed by expectant conservative ma nagement without elaborate, risky, or terminal interventions.