Unilateral Lambdoid Synostosis Research Articles

Utilizing Computer-Assisted Design and Virtual Surgical Planning for Correction of Unilateral Lambdoid Synostosis: Erratum.

Utilizing Computer-Assisted Design and Virtual Surgical Planning for Correction of Unilateral Lambdoid Synostosis: Erratum.

Three-dimensional Analysis of Facial Asymmetry in Unilateral Lambdoid Craniosynostosis.

Unilateral lambdoid synostosis (ULS) is characterized by occipital flattening, mastoid bulging, and contralateral parietal bossing. Anterior craniofacial features are less well-defined. This study utilizes volumetric, craniometric, and composite heat maps of three-dimensional (3D) rendered CT scans to analyze anterior craniofacial asymmetry in ULS and compared to controls. A retrospective review of three-dimensional CT scans. Tertiary care pediatric institution. 30 ULS and 30 control patients. Volumetric and craniometric analysis of the anterior fossa, orbits, zygomas, maxilla, and mandible was performed. The anterior fossa volume was greater bilaterally (0.047, 0.038), and the fossa angle was more anterior contralaterally (<0.001) and more anterior bilaterally than controls (0.038, 0.033). The orbits had greater height and lesser depth bilaterally compared to controls (0.006, 0.009; < 0.001, < 0.001). Zygoma length was significantly greater on the contralateral side than controls (0.048; < 0.001). Nasal contralateral deviation of 3.57 ± 1.97°. The maxillary length was longer on the contralateral side (0.045). The mandibular angle was more anterior on the ipsilateral side and posterior on the contralateral side (<0.001) compared to controls (0.042, < 0.001). Chin had a contralateral deviation of 1.04 ± 3.74°. ULS has significant asymmetry in the anterior craniofacial skeleton. There is a bilateral expansion of the anterior cranial fossa with greater frontal bossing on the contralateral side. Increased orbital height and decreased depth. Contralateral zygomatic and mandibular body lengthening with posterior mandibular deviation. These features may provide more effective diagnosis and potential clinical management strategies.

Three-Dimensional Composite Heatmaps of Unilateral Lambdoid Synostosis and Deformational Plagiocephaly

Background: The differentiation of unilateral lambdoid synostosis (ULS) and deformational plagiocephaly (DP) is vital to provide appropriate treatment intervention. Three-dimensional (3D) photo grammetry provides rapid, reproducible image capture without radiation exposure. Advanced analytical methods can help identify distinctive features to differentiate the two craniofacial conditions. This study uses 3D photogrammetry of ULS and DP patients to analyze the global cranial morphology for diagnostic differentiation. Methods: A retrospective review of 3D photogrammetry of 19 ULS and 25 DP patients were analyzed. Cranial vault asymmetry index, oblique cranial length ratio, and diagonal difference were measured. 3D photogrammetry-based composites were created and overlaid on age and gender-matched controls to generate heat maps representing morphologic differences in contour. Results: Cranial vault asymmetry index and oblique cranial length ratio were significantly different between ULS and DP (0.019; 0.022). 3D photogrammetry ULS composite showed retrusion in the ipsilateral occipitoparietal area, contralateral posterior parietal projection, contralateral frontal projection, relative ipsilateral mastoid bulge, and facial projection. DP composite showed unilateral occipital projection and contralateral anterior projection. The contralateral occipital regions in the occipital and anterior areas remained equivocal to control patients. Conclusions: Diagnostic differentiation of ULS and DP has previously relied on observation and linear measurements of cranial asymmetry in a single plane. 3D photogrammetry composites provide a global contour evaluation for diagnosis and longitudinal outcome analysis.

Cranial Shape Changes in Nonsyndromic Unilateral Lambdoid Synostosis after Open Posterior Vault Remodeling.

The purpose of this study was to quantify change in cranial morphology in patients with nonsyndromic unilateral lambdoid craniosynostosis (ULC) from presentation (t0), after open posterior switch-cranioplasty (t1), and at 2-year follow-up (t2). Volumetric, linear, and angular analysis were performed on computed tomographic scans at the three time points and against normal control subjects. Significance was set at P < 0.05. Twenty-two patients were included. ULC cranial vault asymmetry index was higher than in control subjects before surgery (6.22 ± 3.55) but decreased after surgery (3.00 ± 2.53) to become comparable with the normal asymmetry range present in the controls. After surgery, both diagonals increased, but more on the fused side. In the 2 years after surgery, both diagonals in patients with ULC grew proportionately, but the fused diagonal remained slightly shorter than the patent side. Total cranial volume was higher in patients with ULC than in control subjects after surgery but became comparable at t2. Cranial base angulation improved by t2 but did not approach normal, and ear position remained unchanged. The facial twist was higher than in controls at t0 and t1 but was comparable at t2. Coronal asymmetry improved with surgery but remained undercorrected at t2, with the greatest residual asymmetry at opisthion. Open-switch cranioplasty normalizes cranial vault asymmetry index by increasing the fused cranial diagonal more than the patent side and is stable at 2 years. Skull base twist does not normalize, but facial twist approaches normal. Technique improvement should focus on residual coronal asymmetry present at opisthion. Therapeutic, IV.

Utilizing Computer-Assisted Design and Virtual Surgical Planning for Correction of Unilateral Lambdoid Synostosis.

Unilateral lambdoid synostosis is the rarest form of single-suture craniosynostosis. Although various surgical approaches have been described, cranial vault remodeling remains the predominant approach. To aid in surgical planning, preoperative virtual surgical modeling using a patient's presenting computed tomography scan can be used to increase reconstructive precision and to reduce operative time. Presented is a 7-month-old male with unilateral lambdoid synostosis who underwent medically modeled cranial vault reconstruction.

Rotation Advancement Distraction Osteogenesis Technique is Attributed to Unilateral Lambdoid Synostosis and is Used to Correct Posterior Plagiocephaly.

Unilateral lambdoid synostosis is the rarest form of craniosynostosis. Surgical correction is technically challenging from a morphological standpoint and is used to decompress intracranial pressure. Herein, the authors present a "rotational advancement bone flap" technique for the repair of posterior plagiocephaly. A bicoronal skin incision was performed, to expose the occipital region. The rotational advancement bone flap was designed to hinge off the nonsynostotic side, and it was set up to include an occipital protrusion on the normal side. On the premature side, an advancement bone flap was set up to include the flattened and deformed occipital bone. A titanium cranial distractor, which was attached between the bone flap and the anterior bone. An absorbable plate, which would later become a hinge due to the movement of the bone flap, was attached to the area for reinforcement. The authors technique was able to decompress intracranial pressure with satisfactory esthetic outcomes.

Clinical Features and the Use of Three-Dimensional Imaging for Unilateral Lambdoid Synostosis

True isolated lambdoid craniosynostosis is rare. It requires corrective surgery to prevent intracranial pressure and aesthetic stigma by significant dyscrania. We summarize our case series for lambdoid craniosynostosis outlining the pathophysiology, clinical findings and surgical approaches and outcomes. A retrospective analysis of our data from 2010 to 2020 summarized our cases of true lambdoid synostosis. We have used the medical notes and the radiological findings from computed tomography scans to summarize a case series of isolated lambdoid synostosis. Our case series demonstrated 7 patients with true isolated lambdoid craniosynostosis. In most cases surgical intervention in the form of posterior cranial vault remodeling utilizing a bandeau, based on occipital advancement techniques, has demonstrated the most consistently favorable aesthetic outcome. Surgical referral to a craniofacial center should be sought early in difficult to diagnose cases. Although rare, surgical intervention is indicated to correct potentially increased intracranial pressure and to ameliorate cranial dyscrania.

A case of an infant with unilateral lambdoid synostosis difficult to distinguish from positional plagiocephaly

A case of an infant with unilateral lambdoid synostosis difficult to distinguish from positional plagiocephaly

Distinguishing Craniomorphometric Characteristics of Unilateral Lambdoid Craniosynostosis.

Unilateral lambdoid synostosis (ULS) represents the rarest form of single suture nonsyndromic craniosynostosis. Differentiating between posterior deformational plagiocephaly (DP) and ULS has been difficult due to overlapping clinical findings. Past analyses have been limited by sample size. This study was undertaken to clarify anatomical features of ULS. A multiinstitution study was undertaken, analyzing CT imaging from patients with documented ULS to determine clinical and pathological characteristics. Similar analyses were performed on DP patients to differentiate the 2 conditions. Twenty-seven ULS patient scans and 10 DP scans were included. For ULS patients mean age was 6.6 months, majority male (75%), and majority left-sided ULS (71%). The synostosed side ear was anteriorly displaced in 100% of ULS patients, mean difference of 9.6° (P < 0.001), and inferiorly in 96.3% of patients, mean difference of 4.4 mm, relative to the nonsynostosed side. The posterior fossa deflection (PFD) was deviated 5.9° toward the synostosed side relative to the anterior midline. In DP, there was no significant difference between sides in EAC measurements. The PFD and EAC displacements were significantly smaller in DP relative to ULS (P < 0.001 for each). An ipsilateral mastoid bulge was found in 100% of ULS and 0% of DP on CT imaging. Contrary to some previously published findings, the ear is more anteriorly displaced ipsilateral to the fused lambdoid suture in 100% of ULS patients. Ear position alone is not a reliable indicator to differentiate between DP and ULS. A mastoid bulge is a more reliable indicator of ULS.

A Novel Sand Dollar and Staves Technique for Unilateral Lambdoid Craniosynostosis.

Unilateral lambdoid synostosis (ULS) is the rarest form of craniosynostosis. Due to the associated cranio-caudal shift seen in ULS, surgical correction is technically challenging from a morphological standpoint. Herein, the authors present a novel "Sand-Dollar and Staves" technique for the repair of ULS. A zigzag coronal incision is performed, and an anteriorly-based pericranial flaps are elevated. Prefabricated cutting guides are placed and the calvarium is marked. To treat the flattening on the ipsilateral side, a wedged suturectomy is performed with additional barrel staves. A large circle centered over the bulging on the contralateral side is cut out above the open lambdoid suture. This piece is barrel staved in a radial fashion, leaving the center intact and creating a Sand-Dollar appearance. This disk is then flattened and trimmed. The modified Sand-Dollar is fixed using an absorbable plating system. While gentle pressure is applied to the Sand-Dollar piece as it is being secured, the ipsilateral side demonstrates compensatory filling. Results are evaluated using the Whitaker Classification. Four patients underwent surgical correction with this technique. The procedure was performed at mean age of 11.7 months. The mean operative time was 2.5 hours. Intraoperative blood loss was 50 to 100 ml. Total hospitalization time was 2 to 3 days. No post-operative complications were encountered. Whitaker scores ranged from 1 to 1.5. The mean follow-up was 10 months. The Sand-Dollar and Staves procedure is a novel, single-stage approach for the management of ULS with decreased operative time, blood loss, and hospital stay with satisfactory aesthetic outcomes.

Comparative analysis of cranial vault remodeling versus endoscopic suturectomy in the treatment of unilateral lambdoid craniosynostosis.

Unilateral lambdoid synostosis is the premature fusion of a lambdoid suture or sutures and represents the least common form of craniosynostosis, occurring in 1 in 40,000 births. Cranial vault remodeling (CVR) and endoscopic suturectomy with helmet therapy (ES) are surgical approaches that are used to allow for normal brain growth and improved craniofacial symmetry. The authors conducted a comparative outcomes analysis of patients with lambdoid synostosis undergoing either CVR or ES. The authors conducted a retrospective consecutive cohort study of patients with nonsyndromic lambdoid synostosis who underwent surgical correction identified from a single-institution database of patients with craniosynostosis seen between 2000 and 2018. Cranial growth was measured in head circumference percentile and z score. Nineteen patients (8 female and 11 male) with isolated unilateral lambdoid synostosis were identified (8 right and 11 left). Six underwent CVR and 13 underwent ES. No statistically significant differences were noted between surgical groups with respect to suture laterality, the patient's sex, and length of follow-up. Patients treated with ES presented and underwent surgery at a younger age than those treated with CVR (p = 0.0002 and p = 0.0001, respectively). Operating and anesthesia time, estimated blood loss, and ICU and total hospital days were significantly lower in ES (all p < 0.05). No significant differences were observed in pre- and postoperative head circumference percentiles or z scores between groups up to 36 months postoperatively. No patients required reoperation as of last follow-up. Endoscopic management of lambdoid synostosis is safe, efficient, and efficacious in terms of intraoperative and long-term cranial growth outcomes when compared to CVR. The authors recommend this minimally invasive approach as an option for correction of lambdoid synostosis in patients presenting early in their course.

Three-Dimensional Volumetric Changes in Posterior Vault Distraction With Distraction Osteogenesis.

Distraction osteogenesis (DO) may allow for maximal volumetric expansion in the posterior vault (PV) by overcoming viscoelastic forces of overlying soft tissues. Little evidence exists regarding surgical planning and anticipated 3D volumetric changes pre- and post-operatively. We aim to study the volumetric changes occurring in PV distraction in lambdoid craniosynostosis. From 2007 to 2019, a single institution retrospective review revealed 232 craniosynostosis patients. Fourteen demonstrated lambdoid synostosis (6%), and of those, 11 patients were included in the study due to treatment with PVDO or representative sample. Six patients had unilateral synostosis and 5 had bilateral synostosis. Imaging protocol for PVDO patients included preoperative head CT within 1 month of surgery and 8 weeks following distraction cessation with weekly skull plain films. 3D volumetric analyses were performed on pre and postoperative head CT using 3D Slicer software. Posterior fossa volume (PFV) increased by 38.7% and foramen magnum area increased by 26.9% postoperatively. Unilateral lambdoid craniosynostosis patients had greater increases in PFV versus bilateral lambdoid craniosynostosis patients (63.5% versus 8.9%, P = 0.007). Osteotomy to the asterion was more effective in increasing PFV versus osteotomy to foramen magnum (P = 0.050). Placement of distractor in the inferior third of the lambdoid suture is more effective in increasing PFV versus placement in the middle or top third of the suture (P = 0.041). Highest volumetric increases are seen in unilateral lambdoid synostosis. Extending osteotomy beyond the asterion is not necessary for maximal PV volumetric gain. Placement of distractor in the inferior third of the suture leads to maximal PV volumetric gains.

Novel 1q22-q23.1 duplication in a patient with lambdoid and metopic craniosynostosis, muscular hypotonia, and psychomotor retardation

Craniosynostosis (CS) refers to the group of craniofacial malformations characterized by the premature closure of one or more cranial sutures. The disorder is clinically and genetically heterogeneous and occurs usually as an isolated trait, but can also be syndromic. In 30–60% of patients, CS is caused by known genetic factors; however, in the rest of the cases, causative molecular lesions remain unknown. In this paper, we report on a sporadic male patient affected by complex CS (metopic and unilateral lambdoid synostosis), muscular hypotonia, psychomotor retardation, and facial dysmorphism. Since a subset of CS results from submicroscopic chromosomal aberrations, we performed array comparative genomic hybridization (array CGH) in order to identify possibly causative copy-number variation. Array CGH followed by breakpoint sequencing revealed a previously unreported de novo 1.26 Mb duplication at chromosome 1q22-q23.1 that encompassed two genes involved in osteoblast differentiation: BGLAP, encoding osteocalcin (OCN), and LMNA, encoding lamin A/C. OCN is a major component of bone extracellular matrix and a marker of osteogenesis, whereas mutations in LMNA cause several genetic disorders called laminopathies, including mandibuloacral dysostosis (MAD) that manifests with low bone mass, severe bone deformities, and delayed closure of the cranial sutures. Since LMNA and BGLAP overexpression promote osteoblast differentiation and calcification, phenotype of our patient may result from misexpression of the genes. Based on our findings, we hypothesize that both LMNA and BGLAP may be implicated in the pathogenesis of CS in humans. However, further studies are needed to establish the exact pathomechanism underlying development of this defect.

Surgical correction of lambdoid synostosis - New technique and first results.

Premature craniosynostosis of the lambdoid suture is rare. The use of differential diagnosis to rule out positional occipital plagiocephaly is crucial. Nevertheless, once diagnosed, lambdoid craniosynostosis requires corrective surgery to prevent intracranial harm and aesthetic stigma by significant dyscrania. Operative correction of the lambdoid fusion is often performed by suturectomy and helmet therapy, total occipital remodeling interventions, transposition of occipital bone flaps, or occipital advancement procedures either with or without distraction osteogenesis. We present a simple surgical maneuver to potentially correct the occipital and suboccipital constriction caused by unilateral lambdoid craniosynostosis. Three patients with true unilateral lambdoid synostosis underwent surgery. A straight-line skin incision was created, beginning at the caudal pole of the ipsilateral mastoideal bulge. The incision ran cranially and corresponded to the course of the lambdoid suture up to the posterior fontanel. The periosteum was incised and the contralateral (potent) lambdoid suture was identified at its origin. One burr-hole was created to separate the dura from the intern tabula. Afterwards, a square meander-shaped craniotomy was performed along the assumed course of the lambdoid suture. The squares were then forced apart to form the occipital and suboccipital area into a more rounded shape. The squares were fixed in those positions with resorbable plates or sutures. Pre- and postoperative three-dimensional (3D) photoscans were performed and analyzed with special software to follow the perioperative course of the cranial shape. This new approach minimized the operative time and degree of blood-loss, and rounding of the occipital area was accomplished with only one unilateral intervention. In terms of the available photogrammetric data of two of the patients, the cranial vault asymmetry index, posterior symmetry ratio, and posterior/anterior skull volume ratio were improved but not normalized completely. The measurement outcome, as determined by an automated analysis of the photoscans, however, indicated clear flaws with regard to repeatability. A unilateral approach using a square meander-shaped craniotomy and subsequent inclination may be a suitable surgical method for correcting assorted cases of lambdoid craniosynostosis. Transposition of the occipital bone flaps, subtotal craniectomies of the occipital area, and occipital advancements with or without distraction devices may not be essential in all cases of lambdoid synostosis. However, the reliability of the automated analysis of three-dimensional photoscans must be determined.

Lambdoid Synostosis Versus Positional Posterior Plagiocephaly, a Comparison of Skull Base and Shape of Calvarium Using Computed Tomography Imaging

The differential diagnostics between the common positional posterior plagiocephaly and relatively rare lambdoid synostosis is important due to the differences in their treatment plan and clinical management. However, the clinical criteria for the diagnosis of lambdoid synostosis are not clear since there is a considerable overlap in the features of positional posterior plagiocephaly and unilateral lambdoid synostosis. To systematically evaluate the clinical findings in these 2 patient groups, we quantitatively compared the characteristics of endocranial skull base and ectocranial calvarium in 3D computed tomography, in 9 children (mean age 2.9 years) with unilateral lambdoid synostosis and 9 children with positional posterior plagiocephaly. The groups were sex and age matched. Our results show that the skull bases in the lambdoid synostosis are posteriorly shorter and more twisted than in positional posterior plagiocephaly. Anterior twisting was mild in both skull types. Our study confirmed earlier suggested diagnostic feature: prominent ipsilateral mastoidal bossing downward and laterally in all lambdoid skulls. In positional posterior plagiocephaly the bossing was typically not detected. Interestingly, there was a great variation in the position of the ipsilateral ear and external auditory meatus in both patient groups. Thus, neither antero-posterior nor vertical position of ear is a reliable differential diagnostic feature between lambdoid synostosis or positional posterior plagiocephaly.

Surgical correction for unilateral lambdoid synostosis: a systematic review.

Unilateral lambdoid synostosis is considered to be the rarest form of craniosynostosis. Since the introduction of the Sudden Infant Death Syndrome "back to sleep" campaign, the incidence of unilateral lambdoid synostosis was reportedly increasing. This was proven to be false and a consequence of non-specific diagnostic criteria in excluding suture fusion from deformational changes. This, in turn, led to ambiguity in the literature in terms of features and surgical correction in the 1980s to 1990s. We aimed to navigate the literature for true studies of unilateral lambdoid synostosis and examine the results of their surgical corrections. A systematic review with a defined search strategy. A search on MEDLINE and Google Scholar using strategy: (Unilateral AND ((lambdoid* AND Synostosis) OR (lambdoid* AND Craniosynostosis) OR (Posterior AND Plagiocephaly)) AND (Surgery). Articles were reviewed, and data were compiled into tables for analysis. Seventeen studies were included in this review. A total of 188 patients with unilateral lambdoid synostosis were identified. No patients had major complications (venous sinus tear, neurologic injury, or cerebrospinal fluid leakage). Facial asymmetry was widely noted, and only limited improvement was achieved postoperatively. Auricular displacement was variable and often persisted despite surgery. Neurodevelopment did not deteriorate postoperatively and even improved in several patients. Endoscopic techniques revealed shorter periods of hospitalization, reduced mean estimated blood loss, and no blood transfusion requirements. The timing of surgery at 6 to 12 months was found to be the optimal balance in preventing deterioration in neurodevelopment and allowing favorable cranial growth and morphology. The current evidence is difficult to navigate because of deformational plagiocephaly being misdiagnosed as unilateral lambdoid synostosis. Despite this, we present the only systematic review of all truly identifiable cases of unilateral lambdoid synostosis. Long-term quantitative studies are required to assess the benefits of the various surgical procedures.

Clinical and imaging findings in children with non-syndromic lambdoid synostosis

True unilateral lambdoid synostosis is a very rare type of craniosynostosis. Patients present with unilateral posterior plagiocephaly. The differentiation between frequent, simple positional (deformational) posterior plagiocephaly and lambdoid synostosis is not easy and to date subject of controversy. Accurate and early diagnosis is important, because treatment is different. Simple positional plagiocephaly responds to conservative treatment, but craniosynostosis may require neurosurgical intervention. We analyzed clinical presentation of five patients in whom non-syndromic lambdoid synostosis was confirmed by CT imaging, in one additionally by high-resolution ultrasound, and finally neurosurgical intervention. However, clinical inspection alone did not reliably identify infants with lambdoid synostosis. Diagnosis of lambdoid synostosis is not always possible based on clinical inspection alone. To confirm the diagnosis imaging is recommended. There is evidence that high-resolution ultrasound can be used first-line in the future.

Suitable Indication for the Application of Distraction Osteogenesis

In recent years, cranial distraction osteogenesis (DOG) for craniosynostosis has often been performed in Japan. Since 1998, DOG has been conducted in more than 80 patients with craniosynostosis in our institution. It is now important to define the appropriate indications for the application of DOG for craniosynostosis. From the point of view of our more than 10 years of experience with the application of cranial DOG, posterior enlargement is one of the most appropriate applications. Bilateral posterior expansion is conducted for hypertension because of bilateral lambdoidal synostosis, whereas unilateral posterior expansion is conducted for asymmetry because of unilateral posterior plagiocephaly. Posterior expansion by gradual distraction was conducted for 12 cases. Eight cases of syndromic craniosynostosis and 4 of simple unilateral lambdoid synostosis were included. Clinical and radiological improvement was observed in all cases. Postdistraction computed tomography demonstrated a decrease in digital printing within a few months in all cases. Distraction osteogenesis is a useful procedure for posterior enlargement by gradual expansion and guarantees postdistraction rigidity without collapse in a supine position in bilateral and unilateral lambdoid synostosis.

The Variable Position of the Ear in Lambdoid Synostosis

Isolated unilateral lambdoid craniosynostosis is often confused with posterior positional plagiocephaly because of a general overlap in their clinical presentations; however, distinction between these 2 entities is important because of the differences in appropriate management. Historical literature teaches that ear position is posterior in lambdoid synostosis, whereas it is anterior in positional plagiocephaly. Recently, several cases of anterior ear position in isolated unilateral lambdoid synostosis presented to the Texas Children's Hospital. A review of the cases and literature revealed that there are now 37 cases of unilateral lambdoid synostosis in the literature in which ipsilateral ear position is reported. Twelve cases (32%) had anteriorly displaced ears, 6 cases (16%) were nondisplaced, 7 cases (19%) were displaced posteriorly, 4 cases (11%) anteroinferiorly, 1 case (3%) inferiorly, and 7 cases (19%) posteroinferiorly. Based on this review, it seems that the diagnostic significance of the external ear position is unclear at this point.

Analysis of Differences in the Cranial Base and Facial Skeleton of Patients with Lambdoid Synostosis and Deformational Plagiocephaly

Earlier investigations suggest that the morphologic features of patients with lambdoid synostosis include ipsilateral occipital flattening, an ipsilateral mastoid prominence, downward cant of the posterior skull base to the affected side, and contralateral hemifacial deficiency. These features are absent in patients with deformational plagiocephaly. The authors hypothesize that significant differences in craniofacial morphology exist between patients with lambdoid synostosis and those with deformational plagiocephaly. Craniometric measurements were performed on patients with unilateral lambdoid synostosis (n = 9) and deformational plagiocephaly (n = 12). Measurements were performed on affected and unaffected sides and included posterior fossa deflection angle, petrous ridge angle, middle cranial fossa and anterior cranial fossa area, temporomandibular joint displacement, and maxillary and mandibular dimensions. Appropriate statistical tests were performed. Statistically significant differences in posterior fossa deflection angle, petrous ridge angle, and middle cranial fossa were found between groups. Lambdoid synostosis patients demonstrated a larger petrous ridge angle (p = 0.0001) and middle cranial fossa (p = 3.37 × 10(-6)) on the unaffected side. Deformational plagiocephaly patients exhibited no discrepancies between sides. The mean posterior fossa deflection angle was 10.55 degrees for the lambdoid synostosis group and 3.59 degrees for the deformational plagiocephaly group (p < 0.0001). All lambdoid synostosis patients had deviation of the posterior cranial fossa toward the affected side. Deformational plagiocephaly patients had variable deflection. All lambdoid synostosis patients demonstrated marked posterior displacement of the contralateral temporomandibular joint. Deformational plagiocephaly patients had either symmetric temporomandibular joint position (75 percent) or slight contralateral posterior displacement (25 percent). Mandibular size was not significantly different between groups. Patients with lambdoid synostosis and deformational plagiocephaly manifest significant differences in cranial base morphology, contributing to the phenotypic differences seen in these two groups of patients.