Management of Cerebellar Dysplasia, Chiari I Malformation, Syringomyelia, and Hydrocephalus in a Patient with Bannayan–Riley–Ruvalcaba Syndrome

Background: Bannayan–Riley–Ruvalcaba syndrome thought to be caused by PTEN tumor suppressor gene mutations. Similar to Cowden's syndrome, these patients can develop hamartomas and other benign lesions, as well as malignancy. In addition these patients are known to have macrocephaly and macrosomia at birth and genital freckling in males. The author presents a case of a patient with this syndrome and the triad of a posterior fossa tumor, Chiari I malformation and hydrocephalus.

Case Report: A 27-year-old male presented to our facility after suffering a first-time generalized tonic–clonic seizure. The patient had initial head CT that showed florid obstructive hydrocephalus associated with a right cerebellar hemisphere mass and tonsillar herniation. After recovering from his seizure, the patient admitted to a history of worsening headaches and intermittent hiccups over approximately two to three months but no focal neurologic complaints. An MRI of the brain recapitulated the findings of the CT scan and also suggested that the mass was most consistent with Lhermitte Duclos; a cervical spine MRI revealed a syrinx. The patient proceeded with a right frontal external ventricular drain, posterior fossa craniectomy, C1 laminectomy, expansile duraplasty, and debulking of his dysplastic tumor; he was advised that he may need a staged procedure for CSF diversion. The tumor was infiltrative and had no discrete borders, consistent with the diagnostic impression from the MRI. Postoperatively, the patient had no new deficits and his drain was kept clamped. He could not tolerate his clamp trial. A postoperative MRI evaluating for CSF flow showed a persistent blockage roughly at the level of the rostral fourth ventricle and craniovertebral junction. As such, the patient was counseled to proceed with another procedure for definitive CSF diversion. After a ventriculoperitoneal shunt was placed, the patient's condition improved and he was discharged home.

Discussion: The cause of the patient's hydrocephalus was assumed to be multifactorial. The preoperative MRI did not show significant mass effect on the fourth ventricle from the cerebellar mass. It was thought that the Chiari decompression would help resolve the hydrocephalus because the tonsillar crowding was the presumed culprit. On pathology, the patient was found to have cerebellar dysplasia; more specifically, he had slightly enlarged granule cells that were largely restricted to the ribbons of the cerebellar cortex internal granule cell layer. These neurons were smaller and blander compared with the bizarre ganglion cells associated with Lhermitte Duclos. As such, this type of dysplasia may be unique to the patient's syndrome or specific PTEN deletion that is associated with it.

Conclusion: The patient presents with a complex history that is typically not associated with hydrocephalus or hamartomas of the cerebellum. This case underlies the importance of imaging in patients with PTEN hamartoma tumor syndromes, as well as the optimal strategy, in managing Chiari-I malformation in this population. Because the patient did not improve with the craniectomy and duraplasty, it is possible that exploring the obex could have revealed another source of the obstruction.