Spine Deformity 6 (2018) 621e626 www.spine-deformity.org Case Reports Coronal Vertebral Dislocation Due to Congenital Absence of Multiple Thoracic and Lumbar Pedicles: Report of Three Cases, Review of Literature, and Role of Intraoperative CT Navigation S. Rajasekaran, PhD*, Rishi Mugesh Kanna, MS, FNB, MRCS, Manindra Bhushan, MS, Anupama Maheswaran, DNB, FRCR, Ajoy Prasad Shetty, MS, DNB, Siddharth N. Aiyer, MS, FNB Department of Spine Surgery, Ganga Hospital, 313, Mettupalayam Road, Coimbatore, Tamil Nadu 641043, India Received 1 September 2017; revised 7 December 2017; accepted 18 January 2018 Abstract Study Design: Case report Objective: To present three cases of coronal vertebral dislocation due to congenital multiple thoracic and lumbar pedicle agenesis. Summary of Background Data: Congenital pedicle agenesis is an uncommon condition and is frequently identified as an incidental finding on diagnostic imaging in asymptomatic individuals. This agenesis is frequently limited to a single level and is commonly seen in the cervical and lumbar spine. Methods: We report three patients who presented with multiple thoracic and lumbar pedicle agenesis resulting in coronal vertebral dislocation. The patients presented with progressive kyphoscoliosis deformity. Identification of this malformation on conventional radiographs is difficult, and computed tomographic (CT) scan with 3D reconstruction provides a better delineation of the deformity. Results: Computed tomography showed complete absence of pedicles and dissociation of anterior column from the posterior column, resulting in coronal vertebral dislocation. Magnetic resonance imaging confirmed the absence of pedicles and decreased anteroposterior diameter, causing canal stenosis. Two patients were treated by spanning internal fixation, partial deformity correction, and posterior fusion, with satisfactory results. Conclusion: Coronal vertebral dislocation can be easily missed on plain radiograph because many patients with severe scoliotic deformity have thin or sclerotic pedicles. Computed tomography is essential to demonstrate these anomalies. It is important to recognize pedicle aplasia early to prevent rapid progression of deformity and neurologic deficit. Ó 2018 Scoliosis Research Society. All rights reserved. Keywords: Coronal vertebral dislocation; Scoliosis; Congenital; Pedicle agenesis; Navigation Introduction Congenital absence of a thoracic pedicle is a rare anomaly [1-6], and most reports of aplasia are isolated, asymptomatic, and incidental observations on diagnostic imaging [7-10]. However, multiple thoracic pedicle aplasia is an extremely rare condition. We report three cases of congenital multiple bilateral vertebral pedicle aplasia that Author disclosures: SR (none), RK (none), MB (none), AM (none), APS (none), SNA (none). *Corresponding author. Department of Spine Surgery, Ganga Hospital, Mettuplayam Road, Coimbatore, Tamil Nadu 641043, India. Tel.: þ919843022325; fax: þ91-422-4383863. E-mail address: email@example.com (S. Rajasekaran). resulted in coronal vertebral dislocation and progressive kyphoscoliotic deformity. Case Report Case 1 A 12-year-old premenarchal girl presented with a progressive kyphoscoliotic deformity. There were no clinical features of myelopathy and, radiographs showed a right thoracic scoliosis measuring 63 and a kyphosis of 65 . MRI showed no evidence of spinal cord anomalies, however, due to absent pedicles, there was complete dissociation between anterior and posterior elements resulting in coronal 2212-134X/$ - see front matter Ó 2018 Scoliosis Research Society. All rights reserved. https://doi.org/10.1016/j.jspd.2018.01.011 622 S. Rajasekaran et al. / Spine Deformity 6 (2018) 621e626 Fig. 1. (A, B) Anteroposterior and lateral radiographs showing right proximal thoracic scoliosis. (C) T2 sagittal MRI images showing signal changes in the thoracic cord over the apex of the deformity with absent pedicles. (D, E) Significant spinal canal stenosis (white arrow) is seen. There is a translation in the coronal plane between the vertebral body and the posterior lamina, with cord impingement seen between the vertebral body and the lamina over the concave apex of the curve. (F, G) 3D CT reconstruction of the spine showing absent pedicles with complete dissociation between the anterior and posterior elements at multiple contiguous levels in the thoracic spine. (H) Axial CT images, with the white dotted arrow indicating conventional screw trajectory with likely spinal canal violation. Fig. 2. (A, B) Immediate postoperative radiograph with hybrid construct fixation over the concave side of the curve. Laminar hooks placed at T3 and T5 with pedicle screws at T10 and T12. (C, D) Radiograph at the 27-month follow-up showing partial loss of correction with no implant failure. S. Rajasekaran et al. / Spine Deformity 6 (2018) 621e626 623 Fig. 3. (A, B) Anteroposterior and lateral radiographs showing right proximal thoracic kyphoscoliosis. (C, D) Axial CT images demonstrating absent pedicles with coronal vertebral dislocation and narrowing of spinal canal at T4 and T5 levels, respectively. (E) 3D CT reconstruction images showing absent pedicles at multiple levels, as indicated by the white arrows. (F) Acute proximal kyphoscoliosis with no pedicles seen and overlap between the vertebral body and posterior elements. Fig. 4. (A, B) Immediate postoperative anteroposterior and lateral radiographs showing posterior instrumented fusion using pedicle screw rod construct. (C, D) Radiographs at the 21-month follow-up showing progression in the kyphosis with pullout of the T7 screw. 624 S. Rajasekaran et al. / Spine Deformity 6 (2018) 621e626 Fig. 5. (A, B) Anteroposterior and lateral radiographs showing severe right thoracic kyphoscoliosis. (C, D) Axial CT images showing absent pedicles, severe rotation, and altered vertebral body and posterior elements relationship. (E, F) 3D reconstruction showing absent pedicles extending at multiple contiguous levels from the proximal thoracic to the distal thoracic levels (white arrows). The fusion in the cervical spine is also clearly seen in the images. (G, H) The follow-up radiograph taken at 24 months showing progression of scoliosis and kyphosis. dislocation of spine and marked narrowing of spinal canal (Fig. 1). She underwent posterior instrumented deformity correction using intraoperative AIRO CT-based navigation system (BrainLab AG, Munich, Germany). CT images showed absent pedicles at T2eT9 bilaterally, bilateral L5, and left L4 vertebrae (Fig. 1). Pedicle screws could not be inserted at the involved levels and, alternatively, infra-laminar hooks were placed at T3, T5, and pedicle screws at T10 and T12 vertebrae. Screws and rod was placed only on the concave side to avoid a prominent implant as the patient was very thin. Postoperatively, she had correction of scoliosis measuring 52 and kyphosis measuring 46 . At the 27-month follow-up, there was some loss in correction with a scoliosis of 65 and kyphosis of 75 (Fig. 2). However, there was no failure in the instrumentation noted in the form of rod breakage, screw pullout, or displacement of the hooks. Case 2 A 12-year-old girl, a known case of Pierre Robin syndrome, presented with unsteadiness of gait and progressive S. Rajasekaran et al. / Spine Deformity 6 (2018) 621e626 spine deformity since the age of 1 year. She had a right thoracic scoliosis with preserved motor power; in addition, her deep tendon reflexes were brisk and Babinski sign was positive. The radiographs showed a right thoracic scoliosis measuring 49 and a kyphosis of 61 (Fig. 3). CT scan images showed bilateral absent T2eT6 pedicles, an aplastic right T8 pedicle, and secondary canal narrowing between T2 and T4 because of coronal vertebral dislocation. She underwent navigation-guided posterior surgical decompression at T3eT4 and T1eT7 posterior instrumented fusion using pedicle screw rod construct (Fig. 4). The immediate postoperative radiograph showed kyphosis correction to 55 and scoliosis of 15 . She recovered neurologically with improvement in her gait. At last followup of 21 months, there was some loss of correction with scoliosis of 20 . However, there was progression in the kyphosis to 85 . There was screw loosening and pullout noted at the inferior end of the construct at the T7 level (Fig. 4). The neurologic assessment remained normal and the patient has been advised close observation. Case 3 A 5-year-old girl presented with rapidly progressive deformity of the spine noticed first at 6 months of age. She had a thoracic scoliosis measuring 84 and kyphosis of 123 (Fig. 5). She had weakness of both lower limbs and thoracic myelopathy. The thoracic CT scan showed aplastic thoracic and lumbar pedicles, and MRI was suggestive of significant canal stenosis at T7. The parents were counseled regarding the risk of progression of deformity and neurologic deficit, and need for early surgical intervention. Unfortunately, owing to poor socioeconomic background, financial constraints, and considering the risks of the surgical procedure, the parents refused surgical treatment. The patient was last seen at 24 months’ follow-up in January 2016 with progression of deformity to 130 scoliosis and 105 kyphosis (Fig. 5). Examination documented myelopathic signs; however, she retained independent ambulation. The patient has since been lost to follow-up. Discussion Isolated congenital absence of vertebral pedicles is a rare entity and was first reported by Hadley1 in 1946. Cervical and lumbar pedicle aplasia have been reported ; however, few reports have described thoracic pedicle aplasia. Usually, thoracic pedicle aplasia is often restricted to a unilateral and single-level involvement [7-10]. Presence of multiple pedicle agenesis is extremely uncommon, with only two previous reports [11,12]. Rauzzino et al. reported a 14-year-old boy presenting with progressive spastic paraparesis due to bilateral pedicle aplasia from T4 to T8 with thoracic spinal canal stenosis . Geoffray et al. reported a 9-month-old boy with severe progressive 625 congenital kyphoscoliosis with bilateral thoracic pedicle aplasias from T2 to T9 . During embryologic development, the failure of formation of cartilaginous centers can manifest as a hemivertebra or butterfly vertebra . However, aplasia of the pedicle alone in the presence of other normal spinal elements is rare, and the etiology behind the same is unclear. Tomsick proposed that failure of development of the pedicles may be due to failure of chondrification or due to apoptosis of a normally developed cartilaginous arch before ossification . Congenitally absent pedicle at the thoracic level can be identified on plain radiographs with absent pedicle margins on the AP film . The lateral radiograph may show a spuriously enlarged foramen due to the absent pedicle . Absent pedicles may be misdiagnosed at an early age as pedicles are cartilaginous till 3e6 years, and even CT scans may not be able to identify this condition . In the reported cases, the pedicle margins were absent in Cases 1 and 2, suggesting a congenital nature of deformity. However, in Case 3, it was extremely difficult to identify the abnormality with conventional radiography because of overlapping structures in the vicinity and severe vertebral rotation. CT scans with 3D reconstruction is essential to reveal affected levels clearly, as well as for surgical planning. MRI is required to identify any accompanying spinal cord anomaly and to identify cord compression. The absent pedicle reduces the spinal canal dimensions and can cause a significant compression on the spinal cord, resulting in neurologic deficit. The translation in the coronal plane can further compromise the space available for the cord (Fig. 1). Isolated, unilateral thoracic pedicle agenesis is an asymptomatic condition that is an incidental finding [7-10]. In contrast, multiple pedicle aplasia clinically presents with a kyphoscoliotic deformity. They may be identified late in adolescence, as in Case 1 and 2. This late clinical presentation has been observed in the case report by Geoffray et al. . If not diagnosed early, this rare malformation can result in rapidly progressive deformity and neurologic deficit [11,12]. Absence of pedicles at multiple levels leads to separation of the anterior column from the posterior column, leading to rapid progression of deformity, compromise of the spinal canal dimensions, and difficulty in surgical fixation. Absence of pedicles leads to difficulty in surgical management as well. The most commonly performed technique of posterior instrumented deformity correction using pedicle screws is not possible because of the absence of pedicles as well as distorted anatomical landmarks. Screw insertion based on conventional anatomic landmarks have a very high risk of injuring the cord (Fig. 1). Surgical fixation options include the use of hybrid constructs with judicious use of laminar hooks at levels where pedicles were absent as in Case 1. Case 2 was treated by spanning the malformed levels with pedicle screws at the cranial and caudal levels where pedicle architecture permitted screw insertion. Placement of hooks needs to be carefully planned 626 S. Rajasekaran et al. / Spine Deformity 6 (2018) 621e626 as spinal canal dimensions can be significantly reduced because of coronal plane translation. In such cases, intraoperative CT navigation can provide valuable intraoperative guidance. Case 1 was treated with a unilateral fixation with a hybrid construct that may be suboptimal in terms of adequacy of fixation. However, poor skin and muscle cover on the convex side and absence of pedicles did not allow for a more rigid fixation for fear of a postoperative skin breakdown over the prominent screws. The patient was supplemented with a brace for a 6-month period postoperatively to reduce the risk of failure of fixation. Conclusion Congenital multiple bilateral vertebral pedicle agenesis is an extremely rare condition that may present with a progressive kyphoscoliotic deformity and coronal vertebral dislocation. A high index of suspicion is essential as it can be missed on conventional radiography. Recognition of these anomalies can avert rapid deterioration of deformity, neurological compromise, and intraoperative catastrophes as well. Key points Multiple thoracic and lumbar pedicle agenesis is a rare anomaly. It may present as progressive kyphoscoliotic deformity, spinal canal compromise, and neurologic dysfunction. It can result in dissociation between the anterior and posterior column, resulting in coronal vertebral dislocation. Intraoperative CT navigation can help in recognition of these anomalies and help in management as well. Acknowledgments Funded by Ganga Orthopaedic Research & Education Foundation, Coimbatore, India. References  Hadley LA. Congenital absence of pedicle from the cervical vertebra. Am J Roentgenol Radium Ther 1946;55:193e7.  Wiener MD, Martinez S, Forsberg DA. Congenital absence of a cervical spine pedicle: clinical and radiologic findings. AJR Am J Roentgenol 1990;155:1037e41.  Sheehan J, Kaptain G, Sheehan J, Jane Sr J. 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