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We review our experience with four patients who presented to our Medical Center from 2005-2015 with adult idiopathic occlusion of the foramen of Monro (FM). All patients underwent CT scanning and MRI. Standard MRI was performed in each patient to rule out a secondary cause of obstruction (T1-weighted without- and with gadolinium, T2-weighted, fluid-attenuated inversion recovery [FLAIR] and diffusion-weighted imaging [DWI] protocols). When occlusion of the FM appeared to be idiopathic, further high-resolution MRI with multiplanar reconstructions for evaluation of stenosis or an occluding membrane at the level of the FM was performed (T1-weighted without- and with gadolinium, T2-weighted 3D turbo spin-echo). Occlusion of the FM was due to unilateral stenosis and septum pellucidum deviation in two patients, to an occluding membrane in one, and to bilateral stenosis in one patient. Urgent surgical intervention is mandatory when there are signs of increased intracranial pressure while asymptomatic patients may be managed conservatively. In this patient series, truly bilateral stenotic obstruction of the FM was best managed with ventriculoperitoneal shunt and patients with membranous obstruction or unilateral stenosis with septum deviation were treated endoscopically.

Ventriculoperitoneal (VP) shunt placement is the mainstay of treatment for hydrocephalus, yet shunts remain vulnerable to a variety of complications. Although fat droplet migration into the subarachnoid space and cerebrospinal fluid pathways following craniotomy has been observed, a VP shunt obstruction with fat droplets has never been reported to our knowledge. We present the first reported case of VP shunt catheter obstruction by migratory fat droplets in a 55-year-old woman who underwent suboccipital craniotomy for removal of a metastatic tumor of the left medullocerebellar region, without fat harvesting. A VP shunt was inserted 1month later due to communicating hydrocephalus. The patient presented with gait disturbance, intermittent confusion, and pseudomeningocele 21days after shunt insertion. MRI revealed retrograde fat deposition in the ventricular system and VP shunt catheter, apparently following migration of fat droplets from the fatty soft tissue of the craniotomy site. Spinal tap revealed signs of aseptic meningitis. Steroid treatment for aseptic "lipoid" meningitis provided symptom relief. MRI 2months later revealed partial fat resorption and resolution of the pseudomeningocele. VP shunt malfunction caused by fat obstruction of the ventricular catheter should be acknowledged as a possible complication in VP shunts after craniotomy, even in the absence of fat harvesting.