Characteristic MRI findings in children with achondroplasia

Transcription

1 Characteristic MRI findings in children with achondroplasia Poster No.: C-0843 Congress: ECR 2016 Type: Educational Exhibit Authors: I. Solís Muñiz, E. García Esparza, M. A. Lopez-Pino, G. Albi, S. I. Sirvent, T. Cañas, O. Suárez Traba; Madrid/ES Keywords: Congenital, Diagnostic procedure, MR, Pediatric, Musculoskeletal bone, CNS DOI: /ecr2016/C-0843 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 19

2 Learning objectives Illustrate and describe the typical radiological features in children with achondroplasia, including not only the classical radiographic findings affecting osseous structures, but also brain, spine and musculoskeletal pathology that can be observed in magnetic resonance imaging (MRI). Background Achondroplasia is an autosomal dominant disease originated by a mutation of the fibroblast growth factor receptor 3 (FGFR3) gene on chromosome 4 at 4p16.3. It is caused in 80% of cases by a new mutation [1], which increases the FGFR3 function. The FGF3 protein is an inhibitor of the endochondral bone growth by its negative action on proliferation and differentiation of growth plate chondrocytes. Its estimated incidence is between 1/ /30000 livebirths [2], with males affected more frequently than females. There are characteristic clinical features ( Fig. 1 on page 2 ) present at birth, such as short limbs (micromelia), especially in the proximal segment, also known as rhizomelia. The hands are short and broad, and the trunk is long and narrow. The head is large with frontal bossing and the midface is hypoplastic, leading to short Eustaquian tubes, small pharynx and large tonsils and adenoids. The cranio-cervical junction is small, frequently with hydrocephalus and cervical cord compression, which may lead to cardiorespiratory and sleep disfunction. Spinal stenosis and neurogenic claudication are common in late adolescence and adulthood. Most patients with achondroplasia have normal intelligence. If there is clinical suspicion at birth, skeletal radiographs can be used to confirm the diagnosis. Images for this section: Page 2 of 19

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4 Fig. 1: Figure 1. 3-year-old boy with achondroplasia with typical features such as rhizomelic micromelia. Horton WA, Hall JG, Hecht JT (2007) Achondroplasia. Lancet 370: Page 4 of 19

5 Findings and procedure details There are classical osseous deformities in which the radiologic assessment plays a major role in diagnosis. Occasionally, children with achondroplasia present with clinical symptoms not strictly related to those classical features, as for example knee pain unrelated to genu varum or spinal stenosis, that may need MRI studies. Limbs: Micromelia: Generalized shortening of the extremities. Rhizomelia: Shortening and thickening of proximal long bones, femurs and humeri. Metaphyseal flaring or cupping: narrowing of the diaphysis and widening of the metaphysis. Hips: Fig. 2 on page 8 Fig. 3 on page 9 Short femoral necks Flat acetabular roofs Hemispheric capital femoral epiphyses Sagging rope sign [3]: dense convex line overlying the proximal femoral metaphysis on anteroposterior (AP) views. It is also observed in Perthes disease. Prominent lesser trochanter Proximal femoral ovoid lucency, only in infancy Knees: Fig. 4 on page 9 Fig. 5 on page 10 Fig. 6 on page 11 Distal femoral and proximal tibial angulation Inverted V-shape of the distal femoral physis Other common features in MRI [4]: Discoid lateral meniscus: thick and wide meniscus extending medially towards the intercondylar notch, more susceptible to tearing. Patella baja: abnormally low lying patella. It is considered when the Insall-Salvati index (patellar tendon length / patellar length) is < 0.8. Vertical orientation of the anterior cruciate ligament (ACL) with respect to deep femoral notch: There is an increased ACL-Blumensaat line angle, which is the angle calculated by drawing a line parallel to the roof of the intercondylar Page 5 of 19

6 Legs: Fig. 4 on page 9 Brachydactyly: Shortening of metacarpals and sometimes proximal phalanges. They are also of similar length. Trident hands: separated third and fourth fingers Pelvis: Fig. 2 on page 8 Cortical hyperostosis at deltoid insertion on anterolateral humerus Posterior bowing of the distal humerus Hands: Fig. 7 on page 12 Prominent tibial tubercle apophyseal region, due to prominent muscle insertions Fibula overgrowth Arms: Fig. 7 on page 12 notch (Blumensaat line) and one parallel to the distal portion of the ACL. It is normal when <15º. Taut posterior cruciate ligament (PCL): elevated PCL angle, angle formed by intersecting lines through the tibial and femoral segments of the ligament. Normal measures are º in children and young adults. Deep A-shape dysplasia of the intercondylar notch Elevated femoral notch index: ratio between depths of the femoral notch and the condylar notch. Normal 0.5 (±0.05). Small and squared (elephant ear-shaped) iliac wings Narrow sacrosciatic notches Champagne glass shaped pelvic inlet Head: Fig. 8 on page 13 Fig. 9 on page 14 Fig. 10 on page 15 Skull: The skull vault is formed by membranous ossification, so it is not affected and develops normally. As the skull base forms by enchondral ossification, so affected by the disease, there is a marked discrepancy in relative size between vault and base. Typical deformities are: Large skull with prominent forehead Page 6 of 19

7 Hypoplasia of the midface. Consequently, the Eustaquian tubes are short, pharynx is small and the tonsils and adenoids are large for the available space. Small skull base and consequently: Narrow foramen magnum with secondary cervicomedullary compression that can result in high cervical mielopathy. There are studies [5] that demonstrate that around 40% of asymptomatic patients with achondroplasia have T2 hyperintense lesions in the upper cervical cord with no focal compression, probably representing gliosis. Hydrocephalus, mainly occurring because of increased venous pressure due to the narrowed jugular foramen. Short clivus: this originates an enlarged suprasellar cistern ± empty sella due to normal brain and brain stem but a short clivus. Straight sinus vertically oriented Increased tentorial angle: angle measured between a line connecting the nasion with the tuberculum sellae and the angle of the straight sinus. Normal measure is between 27 and 52 degrees. Small or absence of cisterna magna Enlarged CSF and ventriculomegaly Thorax: Fig. 11 on page 16 Small, with shortened and anteriorly splayed ribs Spine: Fig. 11 on page 16 Fig. 12 on page 17 Thoracolumbar kyphosis with anterior wedging of the vertebral bodies producing a bullet-shaped vertebra Posterior vertebral scalloping Increased angle between sacrum and lumbar spine Widening of intervertebral discs Progressive shortening of the pedicles: the altered enchondral ossification results in early fusion of the pedicles to the vertebral bodies. Decreased interpedicular distance: the normal interpedicular distance widens from L1 to L5, but in achondroplasic patients it progressively decreases. Due to these last three features, there is Page 7 of 19

8 Spinal canal stenosis: there is a significant correlation between the cross-sectional area of the spinal canal at higher lumbar levels and the development of symptoms of stenosis, frequently in the third decade or later [1]. Images for this section: Fig. 2: 17 year-old male with achondroplasia. Typical findings in hips: short femoral necks (broad white arrow), flat acetabular roofs (thin black arrow), hemispheric capital femoral epiphyses (asterisk), sagging rope sign (thin white arrows), prominent lesser trochanter (white arrowheads). Classical features in pelvis are also observed: small and squared iliac wings, narrow sacrosciatic notches and champagne glass shaped pelvic inlet. Page 8 of 19

9 Fig. 3: 17 year- old male with achondroplasia (same patient than figure 2). Axial CT (a) and T1-weighted MRI in axial (b) and coronal (c,d) planes show short femoral necks (broad white arrow), flat acetabular roofs (thin black arrow), hemispheric capital femoral epiphyses (asterisk), prominent lesser trochanter (black arrowhead). Fatty infiltration of lumbosacral paravertebral, gluteal and pertrochanteric muscles is also noted. Page 9 of 19

10 Fig. 4: 8 year-old achondroplastic child. Classical findings in knees and legs are present: genu varum with distal femoral and proximal tibial angulation, metaphyseal flaring, inverted V-shape of the distal femoral physis (discontinuous line) and long fibula. Page 10 of 19

11 Fig. 5: MRI of an 8 year-old achondroplastic child with lateral knee pain. a. Coronal T2-weighted gradient-echo MRI image (a) shows inverted V-shape of the distal femoral physis (dotted black line). B. Coronal fat-saturated proton density-weighted demonstrates thick discoid lateral meniscus (arrow) with no signs of tear. c,d. Axial fat-sat PD images show a deep A-shape dysplasia of the intercondylar notch (white discontinuous line), and an increased femoral notch index (#/#). Page 11 of 19

12 Fig. 6: MRI of a 8 year-old achondroplastic child with lateral knee pain (same patient than fig 5). Sagittal T1-weighted images show patella baja (#/# is < 0.8) (a), vertical orientation of the ACL (b) and taut PCL (c). Page 12 of 19

13 Fig. 7: Radiograph of a 10 year-old girl with achondroplasia. Shortening and bowing of the humerus is noted, with cortical hyperostosis at deltoid insertion (arrow), brachydactyly and trident hands. Page 13 of 19

14 Fig. 8: Lateral (a) and AP (b) view of a child with achondroplasia show the large skull with prominent forehead, midface hipoplasia and short clivus. Page 14 of 19

15 Fig. 9: Head MRI of a 19 year-old male with achondroplasia. Sagittal T1-weighted (a) and axial T2-weighted images at the level of the foramen magnum (b). Note the narrowed foramen magnum (arrows), increased tentorial angle (dotted lines), short clivus (arrowheads) with enlarged suprasellar cistern (asterisk) and absence of cisterna magna. Page 15 of 19

16 Fig. 10: Neonatal brain ultrasound in coronal (a) and sagittal (b) plane of a child with achondroplasia. Enlarged CSF spaces over the cerebral hemispheres (asterisk) are present. MRI of the same child 2 years after, with sagittal T1-weighted (c), sagittal CSF flow study (d) and coronal T2-weighted sequences. Enlarged CSF spaces and ventriculomegaly are now present, with mild stenosis of the foramen magnum. CSF flow study shows flow anterior to the brainstem and cord, but not posterior. A spontaneous third ventriculostomy is depicted (white arrows), also demonstrated as a flow artifact in coronal T2w image (black arrows). Page 16 of 19

17 Fig. 11: a. Lateral radiograph in an affected 3 year-old child. Short and anteriorly splayed ribs are noted. Classic vertebras with short pedicles, bullet-shaped vertebral bodies and posterior scalloping are also demonstrated. Increased angle between sacrum and lumbar spine is also present. b. Axial CT image (b) and tridimensional reconstruction (c) of a 17 years-old male showing short pedicles (arrows), marked gibus with bullet-shaped vertebra. Page 17 of 19

18 Fig. 12: T2 weighted MRI of the same child with achondroplasia at 6 months (a) and 8 year-old (b, c, d). Mid-sagittal images show progressive shortening of the pedicles with spinal canal stenosis. Axial images demonstrate widening of intervertebral discs (arrowheads) and triangular configuration of the spinal canal. Page 18 of 19

19 Conclusion Achondroplasia is a complex skeletal dysplasia with many characteristic radiographic findings. There are well known MRI features in brain and spine studies, but there are other MRI musculoskeletal findings such as discoid lateral meniscus we should be aware of. Personal information References Carson BS, Rigamonti D, Ahn ES. Achondroplasia and Other Dwarfisms, in Winn HR (ed): Youmans Neurological Surgery, 6/e. Philadelphia, Elsevier, 2011, Horton WA, Hall JG, Hecht JT. Achondroplasia. Lancet 2007;370: Shingade VU, Song HR, LEE SH, Suh SW, Oh CW, Hong JS. The sagging rope sign in achondroplasia - different from Perthes disease. Skeletal Radiol 2006; 35: Akyol Y, Averill LW, Atanda A, Kecskemethy HH, Bober MB, Mackenzie WG. Magnetic Resonance evaluation of the knee in children and adolescents with achondroplasia. Pediatr Radiol 2015; 45: Brouwer PA, Lubout CM, van Dijk JM, Vleggeert-Lankamp CL. Cervical highintensity intramedullary lesions in achondroplasia: aetiology, prevalence and clinical relevance. Eur Radiol 2012; 22: Dwek J, Lachman R. Skeletal Dysplasias and Selected Chromosomal Disorders, in: Coley B (ed): Caffey's Pediatric Diagnostic Imaging, 12/e. Philadelphia, Elsevier Saunders, 2013; Kao SC, Waziri MH, Smith WL, Sato Y, Yuh WT, Franken EA. MR imaging of the craniovertebral junction, cranium and brain in children with achondroplasia. AJR 1989; 153: Page 19 of 19