Extracerebellar ectopic brain tissue in the posterior fossa

Abstract

Intracranial extracerebral ectopic brain tissue (also called glioneuronal heterotopia) is encountered in rare developmental disorders. These lesions are mainly located at the base of the brain in the supratentorial region and are frequently associated with craniofacial anomalies. We report the prenatal sonographic and magnetic resonance imaging (MRI) findings of isolated extracerebellar ectopic brain tissue in the fetal posterior fossa, which was confirmed by postnatal MRI examination in a healthy infant. A 27-year-old woman at 28 weeks’ gestation was referred to our department with the diagnosis of a round mass in the fetal posterior fossa located in the cisterna magna, which had been identified on a routine ultrasound scan. Ultrasound examination (Antares, Siemens, Munich, Germany) confirmed the presence of a round echogenic non-vascularized mass of 12 mm in diameter located in the midline of the cisterna magna posterior to a normal vermis (Figure 1). The cerebellum was anatomically normal with a normal transverse cerebellar diameter for gestational age (32 mm). The size of the cisterna magna was also within normal ranges. No other structural cerebral or extracerebral abnormalities could be seen. Biometric parameters were normal for gestational age. Fetal cerebral MRI showed a round and apparently solid mass, posterior to the vermis, with a signal similar to that of normal brain tissue on T2-weighted imaging (Figure 2) and with no hemorrhagic changes on T1weighted imaging. Vermian and hemispheric cerebellar anatomy were normal. Although this lesion has not been described previously in this location, imaging findings were suggestive of ectopic/heterotopic cerebral tissue. On the basis of normal cerebellar anatomy with a complete vermis and otherwise normal cerebral and extracerebral anatomy and, following prenatal counseling with neuropediatricians, the couple decided to continue with the pregnancy. Follow-up at 33 weeks’ gestation found the MR signal, size and echogenicity of the lesion to be unchanged. Since the patient was lost to follow-up for