Agenesis of Anterior Falx Cerebri in Patient with Planned Interhemispheric Approach to Third Ventricle Mass.

Abstract

Complete or partial agenesis of the falx cerebri may occur in pediatric patients with developmental anomalies. However, isolated agenesis of the falx in a developmentally normal adult is exceptionally rare. We describe the first reported case of a patient with a third ventricular mass associated with partial agenesis of the anterior falx cerebri, a circumstance that influenced surgical access to a third ventricular epidermoid cyst. A 60-year-old developmentally normal woman presented with progressively worsening aphasia and altered mental status. Brain magnetic resonance imaging showed obstructive hydrocephalus from a third ventricular mass. An anterior interhemispheric transcallosal approach was planned to remove the tumor. However, upon dural opening there was no evidence of a falx cerebri, an anomaly visible but not reported on the prior imaging studies. An interhemispheric fissure was present, but the medial frontal lobes were densely adherent, with multiple traversing veins within the superficial arachnoid of the fissure. Therefore, a left frontal transcortical approach was performed for microsurgical resection of the tumor. Histopathologic analysis identified the lesion to be an epidermoid cyst. Partial agenesis of the falx cerebri is exceedingly rare in a developmentally normal adult, particularly in the presence of an anatomically normal superior sagittal sinus. If present, however, it is important to note this association preoperatively because partial agenesis of the falx cerebri precludes an interhemispheric transcallosal approach to the lateral and third ventricles.