Lambdoid Craniosynostosis

Introduction

Perhaps of all single suture nonsyndromic craniosynostosis cases, premature closure of the lambdoid suture is one of the most difficult ones to diagnose. The primary reason is the confusion of the posterior plagiocephaly from lambdoid synostosis with that of positional deformational plagiocephaly. Since 1992, when the American Academy of Pediatrics recommended that infants sleep supine in order to minimize the incidence of SIDS, there has been an exorbitant increase in the incidence of diagnosed plagiocephaly. However, for surgeons treating craniosynostosis, the diagnosis should not be difficult nor easily confused with deformational plagiocephaly. To summarize it briefly, positional deformational plagiocephaly leads to several key findings when the patient’s head is viewed from above: (1) occipital flattening of the side in constant contact with the crib mattress; (2) ipsilateral anterior movement of the ear on the sided of the plagiocephaly; (3) frontal bossing/prominence of the forehead on the side of the plagiocephaly; (4) flattening of the contralateral forehead; and (5) bossing/prominence of the occiput contralateral to the plagiocephaly. The shape can be seen in an axial computed tomography (CT) scan along with the open suture ( Fig. 13.1A ) which is not the case with true stenosis ( Fig. 13.1B and C ). These morphologic changes give the head an overall look of a parallelogram when viewed from above ( Fig. 13.2 ). Lambdoid craniosynostosis is the least common and most rare form of single suture, nonsyndromic synostosis. The prevalence in the literature varies between 1% and 10%. However, the true incidence is difficult to ascertain because of a body of literature present prior to the mid-1990s which included the so-called “functional” lambdoid synostosis, the “sticky” suture or the “spot welding” of the suture. Analysis of the resected sutures often demonstrated open sutures. The presence of a “sticky” closed suture was corroborated with radiographs of the skull which showed thickening and sclerosis of the suture’s inner table. It is most likely that lambdoid synostosis presented by these authors really represented positional deformational plagiocephaly and not true synostosis. A serious introspective look was taken by the surgical community following the publication of an article on the Wall Street Journal in 1996 describing “A bizarre epidemic 400% increase since 1992” of surgeries for infants with craniosynostosis. These cases were really found to be positional molding cases and not true synostosis. Today it is generally accepted that the true incidence of lambdoid synostosis is between 1% and 5% of all synostosis cases.

Whereas most of the central skull base bones develop via endochondral ossification through an intermediary chondrocranium, the calvaria develops via membranous bone formation. Development and growth of the posterior skull in neonates occurs by a combination of growth of the occipital, parietal bones and the skull base. The lambdoid sutures show the greatest level of proliferative activity around 3 months of age primarily due to the rapid and precipitous growth of the cerebellum which occurs in the first year of life. It is perhaps the profound cerebellar growth that occurs in early infancy that lambdoid synostosis presents with such prominent and pronounced cranial, facial, and skull base changes. Hence, we believe that an early release of the suture would be most beneficial to the patient. This belief is in contradiction to others who believe that surgery should be delayed until 10 to 12 months of age in order to minimize relapse. The treatment of lambdoid synostosis has varied from a simple linear strip craniectomy to much more complex operations to include total posterior vault remodeling and others. Presented in this chapter is our approach using minimally invasive endoscopic craniectomy followed by cranial orthotic therapy.

Clinical Presentation

Unlike other types of craniosynostosis which have a more uniform phenotypic presentation, lambdoid patients have somewhat different characteristics and not all of them share the same physical attributes. The following findings have been found in our cohort of patients with radiographically confirmed lambdoid synostosis: (1) occipital plagiocephaly ipsilateral to the synostosis ( Fig. 13.3 ); (2) a prominent and inferiorly displaced mastoid process on the involved side ( Fig. 13.4 ); (3) inferior downward shift of the ipsilateral ear ( Fig. 13.5 ); (4) a bony and prominent ridge along the stenosed suture ( Fig. 13.6 ); (5) cranial scoliosis with deviation of the vertex to the contralateral side ( Fig. 13.7 ); (6) nasal and mandibular deviation to the contralateral side ( Fig. 13.8 ); (7) turricephaly; (8) prominent and protruding parietal eminence on the contralateral side ( Fig. 13.9 ); and (9) malar asymmetry with anterior displacement on the ipsilateral side. Mostly absent in these patients is frontal asymmetry or plagiocephaly ( Fig. 13.10 ), nor is vertical dystopia seen. When viewed from above, the patients have the prototypical shape of a “trapezoid” ( Fig. 13.11 ) as compared to the “parallelogram” shape seen with deformational positional plagiocephaly (see Fig. 13.2B ). The eyes are typically well aligned in the axial plane.

Diagnostic Radiology

Given the confounding nature of posterior plagiocephaly and the high prevalence of positional plagiocephaly, radiographic confirmation must be obtained in order to confirm the diagnosis of lambdoid craniosynostosis. Plain radiographs have a relatively high sensitivity and diagnosis can be made with a skull series that includes a Towne’s view. The plain x-rays can show typical deformational changes such as cranial scoliosis ( Fig. 13.12 ) and will also show the stenosed and sclerotic suture clearly ( Fig. 13.13 ). However, CT scans ( Fig. 13.14 ), and particularly with three-dimensional (3-D) reconstruction images, are the gold standard for making and confirming the diagnosis. The stenosis pattern is variable and not consistent across patients. The closure of the suture may be limited to a small and focal area ( Fig. 13.15 ) which will still cause significant clinical changes. Partial suture stenosis to include half of the suture or more is a common presenting pattern ( Figs. 13.16 and 13.17 ), as is complete suture closure ( Figs. 13.18 and 13.19 ). A bony ridge over the stenosed suture is another classic finding ( Fig. 13.20 ). Malar asymmetry and the classical downward displacement of the ipsilateral mastoid process can also be readily seen ( Fig. 13.21 ). Stenosis of the lambdoid suture restricts brain growth ipsilaterally and leads to compensatory contralateral parietal growth which is also appreciable on 3-D CT scans ( Fig. 13.22 ).