Pure Bilateral Lambdoid and Posterior Sagittal Synostosis (Mercedes−Benz Syndrome): Case Report and Literature Review

Conventional posterior cranial vault expansion: indications and results-review of the literature

In the late 1980s, craniofacial surgery units reported suboptimal cosmetic results, cranial volume restriction, and intracranial hypertension after anterior cranial vault remodeling in bilateral coronal synostosis associated with severe brachyturricephaly. A possible explanation was a severe associated growth restriction of the posterior calvaria with radiological synostosis at the lambda sutures. "Conventional" or "fixed" posterior cranial vault expansion techniques were developed to address these limitations, sometimes as the first surgical step in a two-staged protocol of total calvarial reconstruction, combined with suboccipital decompression in cases of symptomatic cerebellar tonsillar herniation or, more easily, to resolve the characteristic occipital flattening of lambdoid synostosis. Various surgical approaches have been described; however, the indications for and timing of surgical treatment and postoperative evaluation of results still remain controversial. Although more invasive, conventional posterior cranial vault expansion has proven to be safe and offers a remodeled and protective bony vault immediately after surgery, but the underlying cranial base malformation remained untreated, with implications in the postoperative growth of the facial skeleton. Overcorrection, rigid stabilization, and grafting are also concerns to be addressed.

Posterior Cranial Vault Distraction Osteogenesis Utilizing a Posterior-Superior Distraction Vector in the Treatment of Mercedes Benz Pattern Craniosynostosis

ABSTRACT

Bilateral lambdoid and sagittal synostosis, or Mercedes Benz Syndrome, is a rare complex craniosynostosis resulting in frontal bossing, a tapered posterior fossa, and an anteriorly displaced cranial vertex. Its ideal surgical correction must result in posterior expansion, skull elongation, and caudal repositioning of the vertex. We present a craniometric analysis of skull changes with posterior-superior distraction and introduce a novel craniometric measure: vertex position. In this study, a retrospective review was performed to analyze outcomes of posterior cranial vault distraction osteogenesis (PVDO) using a posterior-superior distraction vector from 2016 to 2019. Cranial vertex position was measured as a fraction of the occipitofrontal diameter from rostral to caudal (0-1.0). Four patients underwent PVDO at mean age 10.61 ± 3.16 months utilizing a posterior-superior distraction vector. Linear distraction distance averaged 30.30 ± 0.90 mm with a mean consolidation period of 3.98 ± 0.72 months. Mean corrected change in intra-cranial volume was 236.30 ± 3.71 mL, at an average rate of 7.81 ± 2.00 mL/mm of distraction. Increases in anterior cranial height (7.83 ± 2.51 mm), middle cranial height (8.43 ± 4.21 mm), posterior cranial height (13.15 ± 7.45 mm), and posterior cranial fossa height (21.99 ± 8.55 mm) were observed. Cranial vertex demonstrated a mean posterior movement of 0.18 ± 0.13. PVDO utilizing a posterior-superior distraction vector for management of nonsyndromic bilateral lambdoid and sagittal synostosis effectively increases intracranial volume and height and provides an esthetic outcome with posterior movement of the cranial vertex.

Synostosis of the lambdoid suture: a spectrum

PURPOSE

Lambdoid synostosis (LS) is a rare condition, which is either isolated; associated with sagittal synostosis, the "Mercedes-Benz" syndrome (MBS); or with synostosis of the coronal sutures (oxycephalic form). In addition, LS is part of the phenotype of a growing number of genetic diseases. The nosology, pathophysiology, and management are controversial. We decided to review our experience with LS.

METHODS

We reviewed retrospectively pediatric cases of LS proved on CT-scanner, isolated or associated with other conditions, followed in our craniofacial center during the last 15 years, regarding clinical presentation, anatomical lesions, syndromic associations, surgical management, and outcome.

RESULTS

We reviewed 48 cases: 6 isolated LS, 22 MBS, and 20 oxycephalic. A syndromic context was present in 72% (up to 80% of oxycephalic cases), and faciostenosis was present in 23%, mostly oxycephalic cases (40%). Transverse sinus agenesis was found in 61% of documented patients. A total of 31% of children had a dystocic birth, up to 45% of MBS. Decompressive craniectomy or cranioplasty was needed in a majority of patients, often young infants, while posterior fossa decompression was mostly performed in older children.

CONCLUSION

LS is rarely isolated and non syndromic; most cases are found in a wide spectrum of diseases, and LS is often associated with sagittal or coronal synostosis. Genetic evaluation is mandatory for LS; conversely, geneticists may require neurosurgical advice for LS in an increasing number of very rare diseases. The surgical management of LS should be tailored according to clinical presentation, age, and syndromic context.

Clinical Features of Bilambdoid and Sagittal Synostosis (BLSS): A Retrospective Multicenter Study in Japan

ABSTRACT

Bilambdoid and sagittal synostosis (BLSS), a rare form of multisutural craniosynostosis, is sometimes known as the Mercedes-Benz syndrome due to the appearance of the fused sagittal and bilateral lambdoid sutures. Although previous studies have described some of its clinical features, the pathology of this disease is not yet fully understood. Moreover, it has been pointed out that BLSS is more common among individuals of Hispanic ethnicity, but its incidence in Asia remains unclear. In the present study, BLSS cases in Japan were analyzed to determine the characteristics of the condition in Japan. Three hospitals in Tokyo participated in the present study. Patients with BLSS who underwent cranial remodeling were included. Data on patient demographics, clinical symptoms, status of the cranial sutures, morphological subclassification, surgical procedures, developmental status, and genetic mutations were analyzed. In total, 22 patients met the enrollment criteria and were included, indicating a higher incidence of BLSS in Japan than in other nations reported in previous studies. In terms of morphological subclassification, there were 15 brachycephalic, 4 dolichocephalic, and 3 normocephalic. For the initial cranial procedure, 7 patients underwent a single-stage cranioplasty, 13 underwent a posterior distraction, and 2 underwent lateral expansion. Patients with a normocephalic cranial morphology tended to undergo surgery at an older age than patients with the other two types. Appropriate timing for surgery is important for healthy development; hence, surgeons should remember that BLSS can lead to "balanced dysmorphism" that may have led to a delay in diagnosis due to its normal-looking morphology.