Title: Transcalvarial parenchymal herniation in the setting of advanced grade Moya Moya disease and morbid obesity
Authors: Jarl Thysell, OMS2; Matias Costa, MD
Introduction
Direct and indirect cerebral bypasses are accepted surgical treatments for Moya Moya disease (MMD). Post-operative parenchymal herniation, in the setting of unrecognized idiopathic intracranial hypertension (IIH), has never been described following surgical bypass for MMD.
Case description
We report a case of a morbidly obese, 31 year old female patient with past medical history of MMD, stroke, type II diabetes mellitus, essential hypertension and tobacco use disorder who underwent bilateral combined cerebral bypasses as treatment for MMD. Following both cases, her immediate post-operative course was unremarkable and she was discharged on post-operative day 3. 10 days after discharge following her right-sided bypass, the patient presented with a severe right-sided headache. Physical exam at that time was non-focal. Computed tomographic angiography (CTA) and magnetic resonance imaging (MRI) were obtained and revealed bilateral parenchymal extracranial herniations through craniectomy defects that were in place to accommodate the combined encephaloduromyosynangiosis (EDAMS) and superficial temporal artery to middle cerebral artery (STA-MCA) direct bypass. The bypasses were patent on CTA. A lumbar drain was subsequently placed to relieve the herniation, which showed high opening CSF pressures, and resulted in gradual clinical and radiographic improvement. Her high CSF pressures, young age, morbid obesity, and lack of other discernible causes on CTA and MRI makes the diagnosis of IIH likely.
Discussion
Risks associated with cerebral bypasses are stroke, hemorrhage, epidural hematoma, and graft occlusion. Parenchymal herniation is a rare complication that has not been reported post-craniotomy for bypass in MMD. Sources of the herniation may have been CSF flow disturbances due to disruption of the arachnoid layer to perform the anastomosis for direct bypasses, and to enhance angiogenesis in indirect bypasses. However, opening the arachnoid layer is common to both modalities and we would expect this complication to be more common. Our hypothesis is that the patient had undiagnosed IIH prior to both bypasses, which is known to affect young obese women. Upon more review, the patient had a history of headaches that were similar in quality to headaches in IIH. Given this history, patient demographics, and lack of other pathophysiological phenomena that could explain her transcalvarial herniations, we believe she had some form of venous hypertension due to her morbid obesity, which was further exacerbated by surgical disruption of the arachnoid layer and craniotomies. Surgeons should be made aware of this potential complication, as herniation may result in cortical contusions, lacerations, and ischemic strokes.
I am one of the judges on your very interesting case. At the end, you mention intracranial hypertension as being contributory. Should this have been discovered prior to the surgery? Would the diagnosis have changed either the procedure/treatment/follow up?
Hi Dr. Callan,
That’s a great question! The reason for the mentioning of IIH at the end was the primary concern of the case report. It was believed that the symptoms of cerebrovascular disease (which can include headaches) and her history of migrainous headaches could have obscured the pursuit of the diagnosis of IIH. IIH is infamously non-specific in nature and some patients will show an empty sella / enlarged subarachnoid space on imaging, or papilledema on fundoscopic exam. None of these findings were present pre-operatively in this patient. After discussing with the team, it likely would not have changed proceedings as the most imminent threat to the patients life was Moyamoya disease. She likely would have had different intraoperative management (more mannitol?), but I have not spoken to anesthesia about this. Post-operatively, the patient still would have required a drain of sorts – whether this would be a lumbar or ventriculoperitoneal shunt is a different question. There are reports of “cerebral hyperperfusion syndrome” post-operatively, which is a more common effect following carotid endarterectomy, “high” flow cerebral bypasses (the graft is the radial artery, instead of using the superficial temporal), or resection of an arteriovenous malformation (AVM). Perfusion studies were normal in this patient when they assessed graft patency, effectively ruling out cerebral hyperperfusion syndrome.
Thanks for listening and engaging!
Sincerely,
Jarl Thysell
Thank you for this very interesting case report, Student Dr. Thysell. I have been assigned as one of the judges for your case report. Can you say anything about the long-term prognosis of Moyamoya, or this case specifically? Given the age of the patient, I would presume she has dealt with significant obesity most of her life – is that an area of focus for her treatment plan? Thanks again.
Hi Dr. Briggs Early,
The long term prognosis following cerebral bypasses is actually pretty good; usually 90% or higher over 5 years. This should be interpreted cautiously when compared to non-surgical candidates; previous studies have shown minimal difference in prognosis in non-surgical vs surgical patients, however, surgical patients are naturally of a higher grade disease, and therefore the surgery is actually significantly beneficial once the sample is adjusted for severity of disease. Without surgery, patients typically suffer strokes and endure long-term deficits and a higher mortality. Some have more indolent disease than others. Following bypass in appropriate candidates, they often do very well with approximately 92% 5 year survival. Long-term management typically involves mitigating the affects of past strokes. Per usual, selecting patients carefully is top priority to ensure good surgical response.
Regarding her obesity- yes, it is a huge priority. In this patient, her case was unique on multiple levels; she had Moyamoya disease (as compared to syndrome), with several other risk factors for cerebrovascular / cardiovascular disease. She had a BMI of 54, HTN, hyperlipidemia, and type II diabetes. These are typically risk factors for Moyamoya syndrome, whereas Moyamoya disease is believed have more of a familial, early onset, more progressive, and bilateral nature to it, regardless of CV risk factors. All of these risk factors can decrease the success of her bypass procedure.
All that to say, her long-term prognosis will be contingent on management of her weight and comorbid conditions. Her hyperlipidemia, HTN, DMII all put her at risk of graft occlusion and worsening cerebrovascular disease. Her weight is a major concern and she is a candidate for gastric surgery. Managing her weight has taken the back seat to treating her Moyamoya disease, as most would not operate on someone with such a high risk for stroke and death. Now that she has completed surgery, I know the next step of the plan is managing her weight, but I am not in touch with her primary care provider. It is a focus, but more difficult to speak on from the perspective of a specialist group. I will say that it is a top priority to manage her weight to ensure she has a good response to her bypasses (and to ensure she gets back to her normal life!). These patients are usually followed long-term, often times >2 years, so I hope to see this addressed.
Sincerely,
Jarl Thysell
Great, thanks so much, Student Dr. Thysell!
Judge: Is the Moyamoya disease itself a risk for cranial hernias? What would the mechanism be? Have you read this paper? https://journals.sagepub.com/doi/abs/10.1177/1941874420980611
Hi Dr. Novak,
It is not a risk factor for cranial hernias and is currently an unreported finding. However, a craniotomy / craniectomy can be a risk factor but the underlying pathology is what will dictate herniation. Craniectomies have been used for traumatic brain injuries or extremely refractive intracranial hypertension. Sometimes these procedures can be followed by a paradoxical herniation, but this is very uncommon.
The paper you mention is interesting and makes an important reference to cerebral vessel compensatory mechanisms in response to pCO2. There is a condition called obesity hypoventilation syndrome, resulting in persistent hypercapnia; this would be especially relevant in my case report with a BMI of 54. Hypercapnia should induce cerebral vasodilation, increased flow, and potentially intracranial pressure. This concept, in the setting of diseased vessels and a revascularization procedure could have caused IIH. This is purely speculative but interesting nonetheless. Sometimes Moyamoya patients undergo a Diamox challenge (acetazolamide) to see their vasdodilatory reserve; most have some degree of impaired vasodilation due to stenosis/occlusive disease. Similarly to a stenotic / occluded coronary artery (coronary steal syndrome is a good one to look up), these vessels often operate at their maximal vasodilatory capacity. Following revascularization, the vessels may not have reset their compensatory mechanisms, and could have caused excess cerebral flow, and therefore intracranial hypertension. Additionally, post-op pain management could have reduced ventilation even further, exacerbating the hypercapnia, and worsening the vasodilatory response. Again, all speculative.
Thanks for engaging. I have lots of fun talking about it.
Sincerely,
Jarl Thysell