Vaulting Further: Cranial Vault Expansion for Craniocerebral Disproportion without Primary Craniosynostosis

Purpose: Treatment of subjects with refractory idiopathic intracranial hypertension (IIH) or shunted hydrocephalus with chronic shunt complications is challenging. What is the role for cranial vault expansion, particularly utilizing posterior vault distraction osteogenesis (PVDO), in these cases? This study assesses medium-term e�cacy of cranial vault expansion in this unique patient population. Methods: A retrospective review was conducted of patients who underwent cranial vault expansion from 2008 to 2023 at the Children’s Hospital of Philadelphia. Subjects who did not have a diagnosis of primary craniosynostosis were included in the study. Demographic information, medical history, and perioperative details were collected from medical records. Primary outcomes were the rate of CSF diversion procedures and resolution of presenting signs and symptoms. Secondary outcomes were perioperative and 90-day complications and reoperation requirement.


Introduction
Cranial vault expansion is the clinical standard for the treatment of craniosynostosis, and is well documented to relieve elevated intracranial pressure (ICP) and prevent the associated downstream sequelae of untreated intracranial hypertension. 1,2However, other causes of craniocerebral disproportion such as idiopathic intracranial hypertension 3 (IIH) and slit ventricle syndrome 4 (SVS) or shunted hydrocephalus requiring multiple and increasing shunt revisions do not have consensus treatment strategies.Treatment for IIH often begins with medical management through weight loss for overweight patients and/or drug therapy. 59][20] Recent evidence from our institution suggested a comparable perioperative safety pro le of posterior vault distraction osteogenesis (PVDO) between patients with craniocerebral disproportion without a primary synostotic condition (i.e.IIH or SVS) and those with syndromic craniosynostosis. 16In that study, the authors also reported a signi cant decrease in shunt operations following PVDO at a median short-term follow-up of 3 years. 16However, the literature on cranial vault expansion in IIH and SVS remains scarce, and little is known about the long-term e cacy of this treatment modality in providing symptomatic relief and reducing CSF diversion-related morbidity.
This study aims to report on the medium-term e cacy of cranial vault expansion in the treatment of subjects with IIH or SVS without primary craniosynostosis.Our hypothesis was that this intervention would resolve presenting symptoms and reduce CSF diversion-related morbidity.Here, we describe the largest series to-date of cranial vault expansion for craniocerebral disproportion without primary major suture craniosynostosis.

Methods
This study was performed following approval from the Institutional Review Board at the Children's Hospital of Philadelphia and in accordance with the principles of the Declaration of Helsinki.A retrospective review was conducted of all patients who underwent cranial vault expansion from 2008 to 2023.Subjects who did not have a diagnosis of major suture craniosynostosis, as con rmed by computed tomography (CT) scan, were included in the study.Demographic information, medical history, and perioperative details were collected from medical records.Primary outcomes were change in rate of CSF diversion procedures and resolution of symptoms related to increased intracranial hypertension, including headaches, visual disturbance, papilledema, and vomiting.Secondary outcomes were perioperative and 90-day complications and reoperation requirement.Descriptive analyses were performed on demographic data, and a one-tailed paired t-test was used to compare continuous variables.All statistical analyses were conducted using JASP (Version 0.18.1,JASP Team, 2023) with signi cance de ned as P < 0.05.

Results
Of 13 included subjects, 8 (61.5%) were male and 10 (76.9%) were White (Table 1).Nine patients (69.2%) had a primary diagnosis of shunted hydrocephalus and 4 (30.8%)patients had IIH.Two patients with IIH had a concomitant diagnosis of minor squamosal suture synostosis without scaphocephaly.Ten (76.9%) patients had a ventriculoperitoneal (VP) shunt at the time of initial vault expansion.Mean age at initial surgery was 5.5 ± 3.6 years, and mean length of hospitalization was 9.7 ± 6.5 days.
There were no apparent intraoperative complications among the cohort.Mean postoperative follow-up was 4.1 ± 2.1 years.Four (30.8%) patients experienced complications within 90 days of surgery, including infection in 2 patients that resolved with antibiotic therapy, and CSF leak in one patient that was likely related to external ventricular drain (EVD) removal in the same time period.Additionally, one patient experienced worsening headaches, blurry vision, and emesis with demonstrated papilledema and elevated opening pressure on lumbar puncture in the postoperative period, with resolution of symptoms over time.Among subjects who underwent PVDO, mean elapsed time between distractor placement and removal was 3.1 ± 0.6 months.

IIH Cohort
Among 4 patients with IIH, three underwent cranial vault expansion after failing medical management of ICP-related symptoms (Figs.1-2).Following discussion with patients and their families, who expressed desire to avoid CSF diversion-related morbidity, PVDO was offered as a potential treatment approach.All 4 patients with IIH demonstrated symptomatic improvement, including resolution of headaches, vomiting, and/or papilledema.None of these patients underwent repeat cranial vault expansion at last follow-up.
One of the 4 patients had experienced several VP shunt-related infections within a few weeks of surgery, and since he was not yet shunt-dependent, PVDO was proposed as an alternative.As of his most recent follow-up at 1.6 years postoperatively, this patient did not require a VP shunt.

Shunted Hydrocephalus Cohort
Among 9 patients with shunted hydrocephalus, 8 underwent PVDO (Figs. 3-4) and one underwent PVR due to parental concern regarding external hardware and the daily distraction requirement.CSF diversion requirement decreased from 2.7 ± 1.6 procedures per year preoperatively to 1.2 ± 1.8 per year following initial cranial vault expansion (p = 0.029) (Fig. 5).Four (30.8%) patients underwent repeat cranial vault expansion for recurrence of presumed ICP-related symptoms, which included headaches, papilledema, and/or change in mental status.Among those requiring reoperation, 3 underwent fronto-orbital advancement due to the presence of anterior cranial dysmorphology, and one underwent repeat PVDO; in 3 of these patients, symptoms resolved following repeat cranial vault expansion.At most recent followup, all 9 subjects had a VP shunt in place, and 7 demonstrated symptomatic improvement of their ICPrelated symptoms.

Discussion
Several important ndings emerged from this study of the effectiveness of cranial vault expansion in alleviating CSF diversion-related morbidity and presenting symptomatology in children with IIH or SVS.Among subjects with IIH, PVDO was associated with long-term symptomatic relief.Although a few patients underwent repeat cranial vault expansion, patients with shunted hydrocephalus still demonstrated a signi cant reduction in the rate of CSF diversion following PVDO/PVR.
Prior reports have investigated the use of cranial vault expansion in the treatment of craniocerebral disproportion without primary craniosynostosis. 16,18-20However, there is limited evidence on the longterm e cacy of this modality in treating IIH and SVS and/or shunted hydrocephalus.In the management of IIH, the goal of therapy is reduction of elevated ICP to preserve vision and resolve associated symptoms. 3First-line treatment for this condition is weight loss in overweight patients 21,22 and/or drug therapy with acetazolamide. 3,5,235][26] Furthermore, certain medications can be associated with signi cant side effects. 23,27hese challenges are compounded in young children, for whom weight loss and/or long-term drug therapy may be inappropriate or intolerable.
In cases of IIH refractory to medical management, surgical intervention may be pursued via optic nerve sheath fenestration (ONSF)-a procedure in which the optic nerve sheath is incised to enable CSF drainage and reduce pressure on the optic nerve-and/or CSF diversion through LP or VP shunting. 57][8]30 Moreover, children may be particularly susceptible to shunt-related complications, possibly due to shunt migration from natural growth or the relative size of shunt tubing in the thecal sac in an LP shunt. 6In some patients with IIH, symptoms are left unresolved by conventional medical therapy, ONSF, and/or CSF diversion. 5 patients who have failed medical management and desire to avoid/reduce morbidity related to CSF diversion, cranial vault expansion may be considered as a treatment modality.In our cohort, 4 patients underwent PVDO for IIH after failing conventional management.Among these patients, all demonstrated symptomatic improvement at long-term follow-up.Moreover, one patient who had previously experienced numerous shunt-related infections was shunt-free at most recent follow-up.A previous study reported symptomatic improvement in 2 of 3 patients who underwent PVDO for IIH at a median follow-up of 3 years. 16Our ndings add to existing literature by providing a longer-term view on the e cacy of PVDO in the treatment of IIH.
Similarly, slit ventricle syndrome-a chronic complication of CSF diversion-and shunted hydrocephalus with multiple recurrent shunt revisions are challenging conditions for which there is no consensus treatment strategy. 41][12][13][14][15][16][17] Furthermore, much of existing literature on the management of SVS consists of case reports or series with limited or varied follow-up; thus, the e cacy of existing treatment modalities is not well understood. 4ranial vault expansion for SVS/shunted hydrocephalus is not a novel treatment approach.An early report from our center studied 12 patients with "slit ventricle syndrome" and post-shunt craniosynostosis and demonstrated improvement in neurologic symptoms following cranial vault expansion via bilateral fronto-orbital advancement with frontotemporoparietal expansion or PVR. 31 However, 10 of these patients had radiologically-con rmed craniosynostosis of major calvarial sutures, while 2 had "functional" synostoses with narrowed/overlapping sutures. 31More recently, our center published a report discussing the short-term outcomes of 6 patients who underwent PVDO for slit ventricle syndrome. 16In contrast to the earlier study, none of these 6 patients had a primary diagnosis of craniosynostosis. 16dditionally, since the publication of the early report, our center adopted PVDO as a preferred modality for cranial vault expansion in patients with cephalocranial disproportion without primary craniosynostosis.In the more recent study, patients with SVS demonstrated a signi cant reduction in shunt rate at a median follow-up of 3 years. 16Our ndings suggest that this reduction in CSF diversion procedures following cranial vault expansion is sustained at medium-term follow-up.
Notably, almost half of the SVS/shunted hydrocephalus subgroup underwent repeat cranial vault expansion, suggesting that in a portion of these patients, initial PVDO may not be a de nitive solution.
The presence of anterior dysmorphology in several of these patients suggest that appearance-related concerns may have also played a role in decision-making for additional surgery.However, this sample may be biased as these patients continued to have symptomatology often without clear signs of elevated ICP, and therefore were di cult to manage.Nonetheless, 7 of 9 patients in our cohort reported symptomatic improvement at most recent follow-up.
At our institution, PVDO is preferred to other forms of cranial vault expansion in patients with cephalocranial disproportion without primary craniosynostosis.There are several reasons underlying this choice.First, PVDO has demonstrated superior volumetric gains in comparison to anterior vault expansion. 32,335][36][37] Finally, preserving the virgin frontal bone allows for increased exibility for future correction of frontal dysmorphology, as appropriate.Nonetheless, the risk of shunt malfunction and infection may be heightened in patients with VP shunts undergoing PVDO; 38 thus, the risk-bene t ratio of this intervention must be considered when determining treatment modality.
While cranial vault expansion is not considered rst-line treatment for IIH or shunted hydrocephalus, in a select group of patients for whom other medical or surgical interventions have failed or caused signi cant morbidity, it may be a reasonable option within a surgeon's armamentarium with promising medium-term outcomes.Potential limitations of this study include its small sample size and the subjective nature of neurological symptoms.Notwithstanding these constraints, we report on the largest series to-date of cranial vault expansion in craniocerebral disproportion without primary major suture craniosynostosis.Intraoperative photo illustrating distractor placement for subject depicted in Figure 3.

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Figure 3 Patient
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Figure 5