What Is the Skull Structure Influence of Squamosal Suture Synostosis in Nonsyndromic and Syndromic Crouzon Craniosynostosis?:

Surgical Management in Isolated Squamosal Craniosynostosis: A Systematic Review

BACKGROUND

Although craniosynostoses involving the major sutures have been well described, the frequency of isolated minor suture craniosynostoses is much lower. Squamosal craniosynostosis (SQS) is a rare form of cranial synostosis, and the paucity of literature has made the creation of a standardized treatment plan difficult. We present a systematic review of the literature on isolated SQS to identify disease characteristics that lead to a need for operative intervention and to delineate patterns in surgical management.

METHODS

A systematic literature review was performed using the electronic databases of PubMed, Scopus, and MEDLINE and the key words "squamosal AND craniosynostosis," "squamous AND craniosynostosis," "squamosal craniosynostosis, "squamosal suture craniosynostosis," and "isolated squamosal craniosynostosis." Only human studies that described presentation and management of SQS were included. A blinded, 2-reviewer analysis of the articles was performed. Data collected included patient and disease characteristics, imaging workup, and treatment specifics, which were analyzed by descriptive statistics.

RESULTS

A total of 19 studies examining 119 patients with SQS were reviewed, with 97 (82%) multisutural cases and 22 isolated cases (18%). Of the isolated cases, 6 (27%) required surgical craniosynostosis repair, of which 1 (17%) had unilateral sutural involvement and 5 (83%) had bilateral involvement. Of the patients with isolated SQS, 7 (32%) had a congenital syndrome and comprised 33% of patients who required surgical intervention. The nonsyndromic patients with isolated SQS who required surgery presented with a wide array of phenotypic findings; 3 patients underwent some form of cranial vault remodeling, whereas 1 patient underwent ventriculoperitoneal shunt only. Of the 4 nonsyndromic patients with isolated SQS who underwent surgical repair, half required operative intervention because of elevated intracranial pressure and the other half because of dysmorphic head shape.

CONCLUSION

The findings of this updated systematic review suggest a trend toward surgical management in bilateral SQS versus unilateral SQS, and that patients with isolated SQS, previously considered to be a nonsurgical finding, should be carefully monitored, as there remains risk of increased intracranial pressure. Pooled systematic review data suggest isolated SQS has a 27% operative intervention rate, with the presence of coexisting syndromic diagnoses increasing that risk.

Squamosal Suture Synostosis: An Under-Recognized Phenomenon

INTRODUCTION

The squamosal suture (SQS) joins the temporal to the parietal bones bilaterally and is a poorly described site of craniosynostosis. SQS fusion is thought to occur as late as the fourth decade of life and beyond; however, we have incidentally noted its presence among our pediatric patients and hypothesize that it may occur earlier in life and more frequently than previously believed.

METHODS

A retrospective review of imaging performed on pediatric patients was completed to identify patients with SQS synostosis. This included a review of clinical notes as well as computed tomography (CT) images obtained by our craniofacial clinic. Relevant patient data and imaging were reviewed.

RESULTS

Forty-seven patients were identified with SQS synostosis, 21 were female (45%). Age at the time of radiographic diagnosis was 10.1 ± 8.4 years (range 17 days to 27 years). A majority of patients had bilateral SQS synostosis (57%), with a relatively even distribution of unilateral right (23%) versus left (19%). SQS was an isolated finding (no other suture involvement) in 15 patients (32%), all of whom were normocephalic and did not require surgical intervention. Thirty-two patients (68%) had concomitant craniosynostosis of other sutures, most commonly sagittal and coronal. Nine patients (19%) underwent surgery to correct cranial malformations-all these patients had multi-suture synostosis (P = 0.012). Twenty-seven patients (57%) had SQS synostosis diagnosed incidentally compared to 20 (43%) who were imaged with suspicion for synostosis. In those who were symptomatic, common findings included developmental delay, elevated intracranial pressure, hydrocephalus, seizures, and visual/hearing impairments. Ten patients (21%) were syndromic, the most frequent of which was Crouzon syndrome. No single pattern of calvarial malformation could be definitively described for SQS synostosis.

CONCLUSION

Given that most isolated SQS synostosis cases were normocephalic, asymptomatic, and discovered incidentally, it is likely that there are many cases of unidentified SQS synostosis. The significance of SQS synostosis is currently unclear, and warrants further investigation into this phenomenon, its natural course, and its potential presence in the spectrum of normal development.

Respective Roles of Craniosynostosis and Syndromic Influences on Cranial Fossa Development

BACKGROUND

Little is known about the detailed growth of the cranial fossae, even though they provide an important structural connection between the cranial vault and the facial skeleton. This study details the morphologic development of isolated cranial vault synostosis and associated syndromes on cranial fossa development.

METHODS

A total of 125 computed tomographic scans were included (nonsyndromic bicoronal synostosis, n = 36; Apert syndrome associated with bicoronal synostosis, n = 24; Crouzon syndrome associated with bicoronal synostosis, n = 11; and controls, n = 54). Three-dimensional analyses were produced using Materialise software.

RESULTS

The regional anterior and middle cranial fossae volumes of nonsyndromic bicoronal synostosis are characterized by significant increases of 43 percent (p < 0.001) and 60 percent (p < 0.001), respectively, and normal posterior cranial fossa volume. The cranial fossae depths of nonsyndromic bicoronal synostosis were increased, by 37, 42, and 21 percent (all p < 0.001) for anterior, middle, and posterior cranial fossae, respectively, accompanying the shortened cranial fossae lengths. The volume and morphology of all cranial fossae in Apert syndrome nearly paralleled nonsyndromic bicoronal synostosis. However, Crouzon syndrome had reduced depths of cranial fossae, and more restricted fossa volumes than both Apert syndrome and nonsyndromic bicoronal synostosis.

CONCLUSIONS

Cranial vault suture synostosis is likely to be more influential on cranial fossae development than other associated influences (genetic, morphologic) in Apert and Crouzon syndromes. Isolated Apert syndrome pathogenesis is associated with an elongation of the anterior cranial fossa length in infants, whereas in Crouzon syndrome, there is a tendency to reduce cranial fossa depth, suggesting individual adaptability in cranial fossae development related to vault synostosis.

Cephalocranial Disproportionate Fossa Volume and Normal Skull Base Angle in Pfeiffer Syndrome

BACKGROUND

Pfeiffer syndrome is a rare syndromic craniosynostosis disorder, with a wide range of clinical manifestations. This study aims to investigate the structural abnormalities of cranial fossa and skull base development in Pfeiffer patients, to provide an anatomic basis for surgical interventions.

METHOD

Thirty preoperative CT scans of Pfeiffer syndrome patients were compared to 35 normal controls. Subgroup comparisons, related to differing suture synostosis, were performed.

RESULTS

Overall, the volume of anterior and middle cranial fossae in Pfeiffer patients were increased by 31% (P < 0.001) and 19% (P = 0.004), versus controls. Volume of the posterior fossa in Pfeiffer patients was reduced by 14% (P = 0.026). When only associated with bicoronal synostosis, Pfeiffer syndrome patients developed enlarged anterior (68%, P = 0.001) and middle (40%, P = 0.031) fossae. However, sagittal synostosis cases only developed an enlarged anterior fossa (47%, P < 0.001). The patients with solely bilateral squamosal synostosis, developed simultaneous reduced anterior, middle and posterior cranial fossae volume (all P ≤ 0.002). The overall skull base angulation, measured on both intracranial and subcranial surfaces, grew normally.

CONCLUSION

Enlarged anterior cranial fossae in Pfeiffer syndrome children is evident, except for the squamosal synostosis cases which developed reduced volume in all fossae. Volume of the middle cranial fossa is influenced by associated cranial vault suture synostosis, specifically, sagittal synostosis cases develop normal middle fossa volume, while the bicoronal cases develop increased middle fossa volume. Posterior cranial fossa development is restricted by shortened posterior cranial base length. Surgical intervention in Pfeiffer syndrome patients optimally should be indexed to different suture synostosis.

Cranial Fossa Volume and Morphology Development in Apert Syndrome

BACKGROUND

Apert syndrome causes normal or enlarged intracranial volume overall as patients grow. This study aimed to trace the segmental anterior, middle, and posterior cranial fossae volume and structural morphology in these patients, to help discern a more focused and individualized surgical treatment plan for patients with Apert syndrome.

METHODS

This study included 82 preoperative computed tomographic scans (Apert, n = 32; control, n = 50) divided into five age-related subgroups. The scans were measured using image processing and three-dimensional modeling software.

RESULTS

The middle cranial fossa volume was increased and was the earliest change noted. It was increased by 45 percent (p = 0.023) compared with controls before 6 months of age and remained increased into adulthood (161 percent, p = 0.016), with gradually increasing severity. The anterior and posterior cranial fossae volumes also increased, by 35 percent (p = 0.032) and 39 percent (p = 0.007), respectively. Increased depth of cranial fossae contributed most to the increase in volumes of patients with Apert syndrome, with correlation coefficients of 0.799, 0.908, and 0.888 for anterior, middle, and posterior cranial fossa, respectively. The intracranial volume was increased 12 percent (p = 0.098) across the entire test age range (0 to 26 years old), but only had statistical significance during the age range of 6 to 18 years (22 percent, p = 0.001).

CONCLUSIONS

Malformation of the middle cranial fossa is an early, perhaps the initial, pivotal cranial morphologic change in Apert syndrome. Increased cranial fossae depth is an inherent characteristic of the maldevelopment. Normalization of cranial volume and circumference overall may not achieve a normal skull structure, as it does not correct regional craniocerebral disproportion.