Ultrasonographic differential diagnosis of fetal intracranial interhemispheric cysts

OBJECTIVE: Ultrasonographic differentiation between intracranial supratento rial interhemispheric pathologic cystlike lesions and those related to phys iologic median structures is essential because the latter have no clinical relevance, whereas the former may carry a poor prognosis. We reviewed our e xperience with 19 consecutive cases of interhemispheric hypoechoic lesions without parenchymal involvement diagnosed between January 1990 and June 199 7 to establish their clinical significance and provide prenatal ultrasonogr aphic criteria to distinguish between pathologic cystlike lesions and those related to physiologic midline structures. STUDY DESIGN: Ail patients underwent targeted prenatal scans of intracrania l anatomy to establish the relationship between the fluid collections and t he surrounding parenchymal and ventricular structures. In addition, a detai led anatomic survey was performed to rule out associated malformations. Fol low-up, including neurologic examination, imaging, autopsy evaluation, or a combination was performed in all cases. Statistical analysis used the Wilc oxon rank sum test, the Fisher exact test, and the chi(2) test for trend. P <.05 was considered significant. RESULTS: Cystlike lesions related to physiologic median structures (n = 12) included enlargement of the cavum septi pellucidi (n = 3), enlargement of the cavum vergae (n = 2), and cysts of the velum interpositum (n = 7). Thes e lesions were unilocular and had a median size of 10 mm (range 10-30 mm); they resolved in 5 cases and remained stable in the remainder. They were no t associated with overt abnormalities, other than borderline ventriculomega ly in 2 cases. Pediatric follow-up (median 26 months, range 3-84 months) sh owed normal neurodevelopment in all cases. pathologic cystlike lesions (n = 7) were significantly larger (median 40 mm, range 10-80 mm, P=.004) and ha d a significantly worsening trend, growing more at serial prenatal ultrason ographic examinations (P=.039) than fluid collections related to physiologi c median structures. Moreover, prenatal ultrasonographic evidence of associ ated intracranial abnormalities, in the form of partial or total agenesis o f the corpus callosum and overt hydrocephalus, was present in 5 of 7 cases of pathologic cystlike lesions and in none of the 12 related to physiologic structures (P =.002). Median gestational age at diagnosis was not differen t between those with cystlike lesions related to physiologic median structu res and those with pathologic lesions (30 and 31 weeks, respectively). Amon g the latter group, 1 pregnancy was voluntarily terminated, 1 infant died a t 4 months of age, 2 infants had neurodevelopmental delay, and 3 infants we re neurologically healthy at a mean follow-up of 43 months. Cyst shunting w as necessary in 5 of 6 cases. CONCLUSIONS: Interhemispheric cystlike lesions related to physiologic struc tures can be prenatally distinguished from pathologic fluid collections on the basis of location, cyst size, change in size with time, and absence of associated anomalies.