Grossly calcified choroid plexus concealing foramen of Monro meningiomas as an unusual cause of obstructive hydrocephalus.

Various intraventricular tumors can present with calcifications; however, the choroid plexus can also have physiological calcifications. This is the first case report of meningiomas located at the bilateral foramen of Monro (FOM), concealed by a grossly calcified choroid plexus, presenting with obstructive hydrocephalus. A 60-year-old woman with disturbed consciousness was admitted by ambulance. Head computed tomography revealed significantly high-density lesions that smoothly extended from the choroid plexus of the lateral ventricles to the third ventricle. They occupied both sides of the FOM, resulting in obstructive hydrocephalus. The diagnostic endoscopic biopsy was performed using a flexible neuroendoscopic system, and an egg shell-like grossly calcified choroid plexus was found to smoothly extend toward the FOM. Resection was not selected because the calcified lesions had tightly adhered to the veins and fornix; therefore, the patient underwent ventriculo-peritoneal shunting. The lesions were histologically identified as psammomatous meningiomas with low proliferation potential (the Ki-67 labeling index was lower than 1%). She was discharged 10 days after surgery without neurological deficits. As calcifications can have tumoral and nontumoral origins, we considered neuroendoscopic exploration to be essential in order to achieve an accurate diagnosis and select optimal management.