Introduction

Lambdoid synostosis is clinically described as posterior synostotic plagiocephaly; consequently, its main differential diagnosis is with forms of posterior positional plagiocephaly, in which the asymmetry of the posterior head is determined by abnormal external forces acting on an intrinsically normal cranium and sutures (Kane et al. 1996). These mechanically induced posterior plagiocephalies (also called deformational palgiocephalies) have become particularly common in the last 20 years following the recommendation “Back to Sleep” by the American Academy of Pediatrics in its campaign in 1992 (Argenta et al. 1996). Current estimates indicate an incidence as high as 8.2% (Boere-Boonekamp and van der Linden-Kuiper 2001; Kane et al. 1996).

On the other hand, the isolated fusion of the lambdoid suture is rare. Population-based studies have demonstrated that the overall incidence of isolated lambdoid suture synostosis is 0.3 in 10,000 births (Matushita et al. 2014), corresponding to less than 1–5.5% of all cases of craniosynostoses (Alden et al. 1999).

Fifteen percent of cases of lambdoid craniosynostosis are bilateral (Vander Kolk and Carson 1994).

Clinical Features

History

To obtain a detailed prenatal history as well as history of the head-shape at birth and its evolution during the first months of life is of paramount importance for the clinical differential diagnosis. Concerning prenatal anamnestic features, a history of intrauterine constriction (twins gestation) and macrosomy may typically suggest a deformational form of plagiocephaly. Similarly, a dystocic delivery may indicate a deformation occurring during the birth process. A premature birth is as well more frequently associated with a positional plagiocephaly due to the frequent long-standing of the babies in the intensive care units in a supine position. Regarding the postnatal period, in positional plagiocephaly parents recall a round head shape at birth, with the flattening deformation developing over the following weeks to months, related almost constantly to an uncorrected preferential position of the head of the baby on one side (Rhodes et al. 2014).

Head Shape Examination

Head shape evaluation should include measurements of head circumference and search for sutural ridging or deformity. During visual assessment, the head should be viewed from the front (facial view), back (posterior view), vertex (bird’s eye view), and side (lateral view) (Ehret et al. 2004).

Patients with positional plagiocephaly usually present with unilateral occipitoparietal flattening. With increased severity, other findings include: anterior displacement of the homolateral ear, forward projection or bossing of the ipsilateral forehead, contralateral occipitoparietal bossing, prominence of the ipsilateral forehead, and consequent flattening of the contralateral forehead (Figs. 1 and 2a, b). The most typical aspect of the head is the one of a parallelogram when viewed from the vertex (Persing et al. 2003).

Fig. 1
figure 1

(a and b) 5 months old child with positional plagiocephaly. The ear homolateral to the positional molding is anteriorly displaced, following the direction of the posterior flattening. C and D = 6 months old child with lambdoid synostosis. Due to the premature closure of the lambdoid suture, the ear homolateral to the synostosis is attracted posteriorly in the direction of the prematurely closed suture

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Fig. 2
figure 2

(a and b) Top view of the head of a child with positional plagiocephaly (a) and lambdoid synostosis (b). The child with positional plagiocephaly (a) shows an anterior displacement of the homolateral frontal region, in the direction of the positional molding. On the contrary the child with lambdoid synostosis (b) shows an attraction to the closed suture of the homolateral frontal region with relative prominence of the contralateral anterior part of the skull. (c and d) 3D CT reconstruction of a child with lambdoid synostosis. It is evident the prominence of the homolateral mastoid and the downward deviation of the C0-C1 axis (c). The internal view of the skull shows a deviation of the midline to the synostotic side (d)

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Conversely the following features usually characterize lambdoid craniosynostosis: ipsilateral occipitomastoid bulge, compensatory contralateral parietal and frontal bossing, and shifting of the homolateral ear inferiorly and posteriorly (though not pathognomonic) (Figs. 1 and 2). The contralateral parietal and ipsilateral occipitomastoid bossing cause the head to be wider posteriorly than anteriorly, resulting in a trapezoid head shape when viewed from above. Also a view of the occiput reveals a tilted cranial base with mastoid deformity and a characteristic “windswept” deformity, as opposed to positional plagiocephaly, which lacks these deformities. Notably, there is also a reduction in posterior skull height on the affected side (Rhodes et al. 2014).

Clearly overlapping positional and synostotic plagiocephaly might exist and should direct the clinicians to perform radiological investigations to support the diagnosis.

Torticollis is a further clinical feature, mostly described in children with positional plagiocephaly, though it might be part of the clinical picture also of infants and children with lambdoid synostosis. Its true incidence is not clear. It has been reported to be from as low as 14.5–20% to as high as 79–84%. For positional plagiocephaly, persistent unidirectional positioning and limited neck motion is thought to contribute to inactivity shortening of the ipsilateral sternocleidomastoid muscle with consequent homolateral deviation of the neck; it might also lead to hemorrhage in the sternocleidomastoid muscle with subsequent scarring or muscle shortening (Losee et al. 2007). In lambdoid synostosis, the posterior occipitomastoid dislocation might contribute to the muscle traction and consequent limit of motion.

Instruments for the Assessment of Deformity

Anthropometric calipers and digital devices with software analysis are available for the clinical diagnosis. Calipers can be used to measure the head length (from glabella to opisthocranion), biparietal diameter (head width), and occipital-frontal transcranial diameters, in addition to measures of head circumference. These measurements are compared in individual patients with age-appropriate norms over time (Mortenson and Steinbok 2006).

Assessment of Severity

The clinician’s evaluation of severity should be part of the child assessment.

The difference between right and left transcranial diameters (the transdiagonal difference) can be used to help calculating the severity of the posterior plagiocephaly. Mild cases are associated with flattening restricted to the back of the skull and a transdiagonal difference of 3–10 mm; moderate cases are associated with malposition of the ear or forehead deformity and a transdiagonal difference of 10–12 mm, whereas severe cases are associated with malar deformity or vertical or temporal skull growth and a transdiagonal difference of greater than 12 mm (Mortenson and Steinbok 2006; Mulliken et al. 1999).

Clinical Assessment in the Case of Bilateral Synostosis of the Lambdoid Suture

In bilateral cases, the entire occipital region is flat and widened (Teichgraeber et al. 2002). This condition is associated with elongation of the vertex to accommodate the growing brain. Both ears are displaced anteriorly and inferiorly (Leboucq et al. 1993). Increased intracranial pressure has been reported in up to 86% of cases. The incidence of Chiari I malformation in bilateral lambdoid craniosynostosis is not exactly known, but might range from 15% to 20% (Zöller et al. 2002).

Radiological Evaluation

Imaging Modalities

Radiography

Historically, skull radiography was a rapid and low-radiation diagnostic tool with specificity of 95% as an initial imaging modality; since the advent of high-speed CT and the reduction of radiation doses, the use of x-Rays as a diagnostic tool has been almost abandoned (Vannier et al. 1989).

Ultrasound Imaging

Normal sutures show an uninterrupted hypoechoic gap between suture margins, whereas synostotic sutures show loss of this hypoechoic space. Less specific signs include loss of beveled edges and irregular thickened margins. The sensitivity of ultrasounds to detect an abnormally fused suture is considered around 70%, the main limits being represented by children older than one year and the inability of the technique to visualize skull base sutures (Blaser 2008).

Computed Tomography Scan (CT)

CT in the evaluation of lambdoid craniosynostosis is almost ever utilized with 3D reconstructions (3D CT) to evaluate both children with clear clinical evidence of synostosis and children with occipital flattening and unclear clinical diagnostic parameters.

The diagnostic accuracy of 3D CT has been reported to be superior to 90% (Blaser 2008). The main role of CT scans is to evaluate the symmetry between the two hemibases, angles, and lengths of the cranial hemifossae (Badve et al. 2013; Sze et al. 2005).

In unilateral lambdoid synostosis, the posterior skull base is tilted downward on the side of the synostosis. Also the anterior skull-base axis (joining crista galli and basion) and posterior skull-base axis (between the basion and opisthion) no longer coincide (Figs. 2, 3, and 4). Because of cessation of growth at the synostotic suture, the posterior skull-base axis swings toward the abnormal suture; for the same reason, the petrous ridge angle (the angle between the petrous bone and the crista galli) is reduced on the affected side, the mastoid process is rotated, and inferiorly deviated and the homolateral maxillofacial structures are retruded and elevated, whereas the controlateral side facial structures are comparatively advanced and downward displaced (Delashaw et al. 1991). In bilateral forms, there is bilateral occipitoparietal flattening with underdevelopment of the posterior fossa (Mulliken et al. 1999; Sze et al. 2005).

Fig. 3
figure 3

Right lambdoid synostosis: a, b, c: 3D CT reconstructions showing the closure of the right lambdoid suture (a), right mastoid prominence and bilateral occipital suboccipital “beaten copper” appearance of the skull (a, b), and anterior rotation of the right condyle (c). d, e: sagittal T1 MR view at the level of the cerebellar tonsils showing unilateral (right = d) protrusion of the cerebellar tonsil through the foramen magnum, the left cerebellar tonsil appearing in normal position (left = e). f: angio MR (from a frontal view) showing a stenosis of the right transverse and sigmoid sinus and of the sigmoido-jugular junction. g: surgical view showing the flattening of the right occipital suboccipital region and the right occipitomastoid prominence; h: surgical view after craniotomy and bone removal showing the stenosis of the right transverse and sigmoid sinus. i: Surgical view at the end of bone remodeling with “barrel-stave” cuts and bone repositioning

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Fig. 4
figure 4

Left lambdoid synostosis: a,b,c: 3D CT reconstructions showing the closure of the left lambdoid suture (a), left mastoid prominence with bilateral occipital suboccipital “beaten copper” appearance of the skull (a,b) and left orbital retrusion (c). d,e,f: axial, sagittal and coronal MR views showing left unilateral protrusion of the cerebellar tonsil; on the sagittal view an initial cervical hydromyelia is documented. g: surgical view showing the flattening of the left occipital suboccipital region and the left occipitomastoid prominence; h, i: surgical view after bone remodeling and bone repositioning with “barrel-stave” cuts both at the level of the bone flap and of the fixed left suboccipital-mastoid region

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MRI

Generally, in patients with isolated lambdoid synostosis MRI is not strictly required. The main role of the MRI is to depict the anatomy of the posterior cranial fossa and craniocervical junction, clarifying the presence and eventually detailing the features of a Chiari I malformation (CM); when a Chiari I malformation is identified, the MR study should include the entire spine to rule out the presence of an hydrosyringomyelia (Cinalli et al. 1995, 2005) (Figs. 3 and 4). Though unusual in children with unilateral lambdoid synostosis, when a Chiari I malformation is present, an MR venogram should be associated, in order to rule out the presence of an homolateral jugular foramen stenosis (Fig. 3).

More recently, new sequences such as “black bone” MR have been proposed as a substitute to 3D CT scans, in order to reduce the radiation risk; this sequence is able to enhance the bone–soft tissue boundary (Eley et al. 2014) (Fig. 5).

Fig. 5
figure 5

(a and b) 5 months old child with left lambdoid synostosis (a). In the frontal view it is evident the contralateral prominence of the maxillary region. (c and d) same patient at 12 years of age. The posterior flattening is satisfactorily corrected (c). On the contrary, the contralateral maxillomandibular region remains prominent as a confirmatory sign of involvement of the skull base in these patients that are not corrected even after an early surgical treatment of the synostosis

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Surgical Management

Though not universally accepted, the timing for surgical correction of lambdoid synostoses corresponds to the usual timing adopted for other cranial sutures synostoses, i.e., between the fourth and the eight month of life (Hormozi et al. 2011).

Surgical Procedure

Bilateral Synostosis

Several methods of reshaping of the parieto-occipital region have been developed. Feasible approaches include star- or spiral-shaped osteotomies (Vander Kolk et al. 1993), exchanging right and left parieto-occipital bones (Vander Kolk et al. 1993), an additional folding of the dura (Jane and Persing 1986), occipital rotation flap (Thaller et al. 1992), and various modifications of the “barrel stave”-osteotomy with subsequent remodeling or reversing the bilateral parietal-occipital segments (Vander Kolk and Carson 1994). Another technique proposed in these cases is to perform a bilateral posterior craniotomy leaving a median-sagittal bone strip as a stabilizing structure around which the reshaped lateral bone segments can be remodeled (Zöller et al. 2002).

Unilateral Synostosis

The most common open surgical technique adopted in the case of unilateral forms of lambdoid synostoses is the unilateral occipital advancement. A posterior bandeau is harvested either horizontally from the middle of the occipital region, or from the vertex of the skull in the coronal plane, depending upon which will give the best correction. A large bone flap is removed from the superior-aspect half of the flattened side. Another bone flap is removed from the inferior aspect of the same. The bandeau is rotated 180 degrees so that the flat side is now overcorrected posterolaterally. The larger upper bone flap is typically reversed as well, allowing overcorrection of the vertical height discrepancy. The reconstruction is then completed below the bandeau. The dura must be meticulously dissected from the bone as both the sagittal and paired transverse sinuses can be partially embedded in the occipital bone (Zöller et al. 2002) (Figs. 3 and 4).

Springs

An alternative to open surgical approaches is represented by gradual occipital expansion through the positioning of springs. An osteotomy line is created following the closed suture and surrounding the occipital bone along the major axis selected for the occipital bone expansion. In the case of unilateral lambdoid synostoses, one, up to three springs are then positioned along the created osteotomy line and fixed through holes made in the calvarium or at the edges of the osteotomy or suture. A resorbable suture is used to anchor the midpoint of the springs to the periosteum to prevent springs dislodgement. The occipital expansion is hence obtained by the opening of the springs, which occurs gradually as far as their force is counteracted by the bone/dura surface resistance (Davis et al. 2010).

The main advantages of springs compared with open surgical procedures are represented by the reduced operative time and the limited perioperative bleeding (Yu et al. 2004). Disadvantages are the risks of skin penetration and dislodgement of the material, as well as the need to remove the system once completed the distraction, a usual timeline in this context being one month from their positioning (Davis et al. 2010). Also the rate of posterior advancement cannot be clearly defined and planned, seen that it depends from the springs forces themselves (Lauritzen et al. 2008).

Distractors

Distraction osteosynthesis has been proposed as a further surgical alternative for the management of lambdoid synostoses, though it has been mainly performed in complex cases. As for other craniosynostoses conditions, the standard distraction protocol, originally introduced by Ilizarov for the extension of tibial bones, entails a latency phase of 5–7 days, a 1-mm/day distraction rate, and consolidation periods of a minimum of one month (Ilizarov 1990). The main parameters to consider when planning a posterior cranial vault distraction are the design of the craniotomy and the type of distractors to be used. Usually for unilateral lambdoid synostosis, a single internal distractor is positioned on the synostotic side, once an osteotomy is performed to open the closed suture, continuing it along the midline and the suboccipital region; the expansion is then gradually obtained having as hinging side the midline. As for springs, operative morbidity, including blood loss and operative time, is reduced performing a distraction osteogenesis, compared with open surgery; the two main disadvantages are represented by an infection rate of 1–3% (Yu et al. 2004; Yonehara et al. 2003) and the need to secondary remove the implanted device (Steinbacher et al. 2011).

Long–Term Follow Up

Beyond the cosmetical correction of the posterior flattening, children with synostotic posterior plagiocephaly should undergo a prospective control of both neurocognitive functions and maxillofacial development. Concerning neurocognitive development, it has been documented that visual function might be compromised already at diagnosis in around 40–50% of the cases (Collett et al. 2005; Miller and Clarren 2000; Shipster et al. 2003). In a personal study on 15 cases operated on between 2001 and 2012, at a mean follow-up of 5.6 years, 80% of the children had attention deficits and 73% had disturbances of oculomanual coordination. Visuo-perceptual functions and praxia were defective in around 50% of the cases. In the Panchal’s study, neurodevelopmental and cognitive delays were reported especially in the group of children with plagiocephaly. The Psychomotor Developmental Index (Bayley Scale of Infant Development-II) indicates significant differences compared with the standard population (p < 0.001). Kordestani and colleagues reported similar results (Kordestani et al. 2006). According to their study, infants with deformational plagiocephaly showed significant delays in both mental and psychomotor development.

SPECT studies have shown a decrease in perfusion to the area of brain under the fused suture in selected cases (David et al. 1996). Generally, negative psychosocial issues may occur with progressive cranial or facial deformity; for this reason, a close follow up in the craniofacial clinic with a follow-up neurodevelopmental testing are adviced (Speltz et al. 2004).

Maxillofacial Deformity

In addition to the distortion of the skull shape, the facial appearance of children with posterior plagiocephaly may be affected adversely by secondary ear displacement and/or mandibular and maxillary deformations (John et al. 2002). Some patients may have changes in facial characteristics secondary to skull base and petrous ridge deformation, which often led to mandibular malalignment. In addition, some children have been found to develop a scoliosis of the face, similar to that seen in anterior plagiocephaly (Goodrich and Argamaso 1996) (Fig. 3). Even in the absence of obvious facial differences, children’s overall attractiveness may be compromised by a plagiocephalic head shape. Not surprisingly, one of the most frequently reported parental concerns regarding posterior plagiocephaly relates to the child’s craniofacial appearance and the possibility that he or she will be teased, embarrassed, or otherwise stigmatized because of the condition (Collett et al. 2005).

The long-term severity of these selected craniofacial deformities may be markedly reduced if these children are operated on early with craniofacial reconstruction techniques (McCarthy et al. 1992). However, facial asymmetry might persist also in children operated on before 1 year of age; similarly the malalignment of the ears, a common finding in this type of craniosynostosis might persist in the long term, whatever surgical correction is performed (Goodrich and Argamaso 1996) (Fig. 3).