Radiologic and pathologic features of spinal dysraphism. A pictorial review.

Transcription

1 Radiologic and pathologic features of spinal dysraphism. A pictorial review. Poster No.: C-0586 Congress: ECR 2011 Type: Educational Exhibit Authors: N. Arcalis, J. L. Ribó, J. Muchart, L. Riaza, J. Blanch Gimenez, M. T. D. MARISTANY, X. pruna, S. Medrano, M Cuadrado ; Granollers/ES, barcelona/es, Barcelona/ES, 4 5 Esplugues de Llobregat, Barcelona/ES, GRANOLLERS/ES, 6 granollers/es Keywords: Inflammation, Infection, Fistula, Education, Diagnostic procedure, Decision analysis, MR, Musculoskeletal spine, Neuroradiology spine, Pediatric DOI: /ecr2011/C-0586 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. Page 1 of 41

2 Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 2 of 41

3 Learning objectives -To describe the principal malformations of the spine and spinal cord seen most frequently. -To summarize the basic concepts about normal and deranged spinal cord embryogenesis. -To offer a practical approach to neuroradiological decision-making. on page 3 Images for this section: Fig. 1:. Page 3 of 41

4 Background Embryological anatomical drawing schemes and correlation of these features with the derangements of the complex cascade of events that characterise early embryonic development. Normal anatomic pictures and MR imaging, identifying the typical neuroradiological appearances: closed and open forms of spinal dysraphism. A "key summary" is also displayed in each section. Imaging findings OR Procedure details INTRODUCTION DEFINITION: The term "dysraphism" ( from Greek ### = bad and #### = suture) Spinal dysraphism is a broad term that includes a variety of disorders in which there is an abnormality in the formation of the spine. The basic defect is an incomplete or absent fusion of the midline mesenchymal, bony and neural structures. Most are diagnosed at birth or in early infancy. Clinical manifestations Variable-sized back mass. Cutaneous manifestations: hairy tuft, naevus, pigmentation abnormalities, hemangioma, sinus tract. Neurological abnormalities Gait disturbances. Club foot. Extremity paresis. Bladder and bowel dysfunction. TERMINOLOGY Open dysraphism exposure of nervous tissue and/or meninges to environment through a congenital bony defect. Closed form is covered by skin + subcutaneous stigmata may be present. Page 4 of 41

5 - Spina bifida: refers to defective fusion of posterior spinal bony elements. - Placode: segment of non-neurulated embryonic neural tissue, frozen at the neural plate stage. - Tethered cord: conus medullaris abnormally low, below L3, associated with postrepair, closed form. IMAGING: Magnetic resonance: has emerged as the most useful noninvasive modality which provides excellent detail of anatomy and characterisation of soft tissue anomalies. Is important to include as much of the brain in order to screen for associated Chiari malformations and hydrocephalus. The most important sequences are: - Sagittal T1-weighted image (WI) : craniospinal axis, delineate vertebral body marrow, cord size, lipomatous tissue. - Sagittal, axial and coronal T2WI: cord parenchyma, delinate cerebrospinal fluid (CFS), extradural interface, associated intraspinal masses, fetal evaluation. - Gradient echo (GRE) in cervical region. - Sagittal and axial planes. Coronal planes are useful in diastematomyelia. Cliniconeuroradiological classification fig.1 on page 12 The incidence of spinal dysraphism is 1-2 cases per 1000 live births. OPEN spinal dysraphism 98% fig2 on page 12 - Myelocele - Myelomeningocele - Hemimyelocele, hemimyelomeningocele CLOSED spinal dysraphism WITH a subcutaneous mass fig.3 on page 13, fig.4 on page 14 - Lipomyelomeningocele - Terminal Myelocystocele Page 5 of 41

6 - Meningocele WITHOUT a subcutaneous mass Simple dysraphic states - Intradural lipoma - Filum terminale lipoma - Tight filum terminale - Persistent terminal ventricle - Anterior sacral menigocele Complex dysraphic states - Diastematomyelia - Dermal sinus - Caudal regression syndrome - Dorsal enteric fistula - Segmental spinal dysgenesis - Neurenteric cysts OPEN spinal dysraphism: is characterised by exposure of the nervous tissue and/or meninges to the environment through a congenital bony defect. IS ALWAYS ACCOMPAINED BY A CHIARI II MALFORMATION, a complex congenital anomaly of the hindbrain. CLOSED spinal dysraphism: there is no exposed neural tissue, although cutnaneous stigmata, such as a hairy naevus, capillary hemangioma, may be present. Some are not clinically evident at birth, it can be present with or without a subcutaneous mass. Embryology fig.5 on page 15 Spinal dysraphism results from derangement in the normal embryogenetic cascade occurring during a limited period, between gestational weeks 2 and 6. Page 6 of 41

7 1. Gastrulation (weeks 2-3): Disorders of notochord formation and integration: caudal regression syndrome, dermal sinus During gastrulation, at the end of the 1st gestational week, changes occurring in the inner cell mass of the bastocyst produce a bilaminar disc composed of two layers, the epiblast (future ectoderm), and the hypoblast (future endoderm). Gastrulation is the process by which the bilaminar disc is converted into a trilaminar disc with formation of an intervening third layer, the mesoblast (future mesoderm).fig.6 on page Primary neurulation (weeks 3-4): Myelomeningocele, myelocele, lipoma with dural defect, intradural lipoma The neural plate is composed of neural ectoderm, which is continuos with cutaneous ectoderm on either side. The cells at the junction of the neural ectoderm and cutaneous ectoderm will eventually differentiate into neural crest cells. At approximately 17 days of gestation, the lateral portions of the neural plate begin to thicked, forming the neural folds. Contractile filaments located in the neuroepithelial cells in the neural folds contract, causing the neural folds to bend dorsally along the entire length of the neuraxis. Neurulation: ( closure of the neural tube) when the neural folds meet in the midline the overlying ectoderm separates from the neural tissue and fuses in the midline. Neural crest cells are extruded. Neural crest cells will migrate to form dorsal root ganglia and multiple other structures.fig.7 on page Secondary neurulation-retrogressive differentation (weeks 5-6): Lipoma of filum terminale, tight filum terminale, terminal myelocystocele fig.8 on page 18 a) A caudal cell mass forms in the tail fold as a result of fusion of neural epithelium at the caudal end of the embryo with the notochord. b) By the age of 30 days, multiple cysts and clumps of cells appear in the caudal cell mass. c) These cysts coalesce to form a tubular structures that unites with the neural tube above d) Retrogressive differentation: 38 days, the cell mass decrease in size through apoptosis and formation of filum terminale. Page 7 of 41

8 OPEN spinal dysraphism fig. 9 on page 19, fig. 10 on page 20 Myelomeningocele and myelocele: The basic defect is caused by an abnormality which occurs at the stage of neurulation that prevents the neural tube from closing dorsally. EPIDEMIOLOGY: + FREQ. #, LOCATION: lumbosacral, lumbar, thoracolumbar and thoracic spine. A segment of the spinal cord (placode) fails to neurulate and protudes, together with the meninges, through a bony defect in the midline of the back, being exposed to the environment. The cord is tethered posteriorly at this level, and the CFS with pia and arachnoid lie ventral to the "neural placode". In myelocele, the neural placode is flush with the plane of the back. DIAGNOSIS: usually suspected antenatally by maternal biochemistry and ultrasound. The neuroradilogist plays a critical part in the assessment of: CHIARI II malformation, associated hydrocephalus, and the complications of myelomeningocele closure ( retethering by scar, dermoid, arachnoid cyst). fig. 11 on page 21, fig. 12 on page 22, fig. 13 on page 23 Hemimyelocele and hemimyelomeningocele are very rare entities, difficult to identify on a purely clinical basis. There is diastematomyelia with one of the hemicords showing a meningocele at its lower end. Abnormality in stage of gastrulation en primary neurulation. CLOSED spinal dysraphism Closed spinal dysraphism is much more heterogeneous than open spinal dysraphism, and a large number of malformations belong to this wide group. Some are not clinically evident at birth, and patients may seek medical atention when complications such as the tethered cord syndrome ensue later in infancy. In general, clinical examination help to restrict differential diagnosis. A critical factor is the presence of a subcutaneous mass in the back. Embryologically, these malformations are related to: Anomalies of gastrulation -Diastematomyelia Page 8 of 41

9 -Dermal sinus -Caudal regression syndrome Anomalies of primary neurulation -Lipoma with dural defect -Intradural lipoma Anomalies of secondary neurulation/retrogressive differentation -Lipoma of filum terminale -Tight filum terminale -Terminal myelocystocele WITH a subcutaneous mass fig.14 on page 24 Lypomeningocele: skin-covered back mass that contains neural tissue, CFS and meninges. Is characterised by the presence of a lipoma or lipomatous tissue that extends from the subcutaneous tissue of the back through the back mass into the spinal canal. The spinal cord is cleft dorsally and tethered at this level to the lipomatous tissue. Myelocystocele consists of a cystic dilatation of the lower end of the spinal cord which represents the dilated terminal end of the central canal enclosed in a skin-covered back mass. The spinal cord is low lying and tethered. MRI: higher signal on T1WI due to its proteinaceous contents. The posterior meningocele consists of a herniated sac of meninges with CSF protruding from the back and covered with skin. WITHOUT a subcutaneous mass Simple dysraphic states Most common abnormalities in children without significant low-back cutaneous stigmata who present with symptoms and signs of cord tethering. A lipoma is a monphyllic mass originating from the mesoderm. Embryologically, lipomas result from early disjunction between neuroectoderm and ectoderm; consists of a localised collection of fat within the intradular space. It is connected to the spinal cord in a Page 9 of 41

10 subpial location but does not infiltrate the cord. There may be an exophytic component of the lipoma. The cord is low lying and tethered to the lipomatous tissue when the lipoma occurs in the lumbosacral area. May be associated with other cord anomalies such as diastematomyelia.on MRI they are isointense with subcutaneous fat in all sequences and give high signal on T1 and T2WI. Location: lumbosacral level, generally subpial. In rare instances, they are completely intramedullary or produce difuse lipomatosis. fig. 15 on page 25, fig. 16 on page 26, fig.17 on page 27, fig.18. on page 28 The filum usually retracts dorsally upon transection. In some patients, the cord is bound down by lipomatous tumors or fibrous tissue, and sacral roots ascending. Lipomas may attach dorsally to the conus and be sessile or pedunculated, other lipomas occupy the distal end of the conus, elongating the latter and terminating in a small lipoma with attached nerve roots. The dorsal and caudal lipomas may occur in combination. Filar lipomas occupy an enlarded filum terminale. fig.19 on page 29 Anterior sacral meningocele: There is an anterior bony defect in the sacrum through which the meningocele sac protudes which is seen as a hyperintense cystic structure on T2-weighted images. The meningocele can also be entirely intrasacral leading to expansion of the sacral canal or even in lateral paraspinal location as in cases of neurofibromatosis. fig.20 on page 30,fig.21 on page 31,fig. 22 on page 32 Complex dysraphic states fig.23 on page 33 Because gastrulation is characterised by the development of the notochord, spinal dysraphism originating in this period will characteristically shows a complex picture, in which the spinal cord, and other organs deriving from or induced by the notochord are severely abnomal. Disorders of gastrulation are therefore also sometimes called complex dysraphic states. In the vast majority of cases, the abnormalities are covered by skin and no tell-tale subcutaneous mass is present. Disorders of midline notochordal integration Notochordal splitting. The differences between these entities result from the different developmental fate of the intervening primitive-streak tissue towards endo-, meso-, ectoderm. They are all share some degree of vertebral abnormality. Dorsal enteric fistula Neurenteric cysts Page 10 of 41

11 Split-cord malformation (Diastematomyelia) Dermal sinus Disorders of notochord formation The abnormality involves the caudal end of the embryo resulting in the caudal regression constellation.including segmentation defects, indeterminate or block vertebra, or absence of several vertebra. Caudal regression syndrome Segmental spinal dysgenesis The dermal sinus is an epithelium-lined fistula which extends inwards from the skin surface and sometimes connects with the central nervous system and its meningeal coating. Found more frequently in the lumbosacral region. Low signal intensity tract is well contrasted against the high signal intensity fat on T1weighted sagittal and axial images. May terminated in an epidermoid or dermoid cyst in the spinal canal or conus with tethering of the cord by these masses which are of high signal intensity on T2-WI and may be high or low signal intensity on T1-WI depending on the nature of their contents. Clinically: dimple, hairy naevus, hemangioma on the skin back. Recurrent meningitis may be an important clinical clue to the diagnosis.fig.24 on page 34,fig. 25 on page 35 Diastematomyelia is one of the most common forms of occult spinal dysraphism. More common in girls. Sites of predilection: lumbar spine and thoracic. Consists of partial or complete sagittal clefting of the spinal cord usually located in the lumbar and thoracic regions. Usually associated with segmentation anomalies of the vertebral bodies (hemivertebra, buterfly vertebra and block vertebra) along with spina bifida extending over several vertebral levels and fusion of the intersegmental laminae. Ther may be a single dura-arachnoid tube around the cleft spinal cord or there may be a cartilaginous, bony or fibrous spur between two hemicords. Well shown on axial T2WI images, and coronal T1WI. High incidence of hydromyelia, lipoma of filum terminale and intradural lipoma. fig.27 on page 37,fig.28 on page 38 Post-surgical spinal dysraphism fig.26 on page 36 Patients who have surgical repair of the dysraphic defect may show deterioration in the postoperative period. Page 11 of 41

12 The causes include retethering of the cord, cord ischemia and cavitation, inclusion lipoma and inclusion epidermoid all of which are very well seen on MRI. MRI is useful for indentification of scar tissue which enhances on contrast administration. Images for this section: Fig. 1: fig.1 Page 12 of 41

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40 Conclusion A basic knowledge of embryogenesis of the spine and spinal cord is a must in order to understand the wide spectrum of abnormalities seen in cases of spinal dysraphism. A rational approach focusing on a correlation among clinical, embryological, and neuroradiological data greatly facilitates the diagnosis. MRI is the single safe modalitiy for best and complete evaluation of these cases. Personal Information References 1.Rossi A, Cama A, Piatelli G, Ravegnani M, Biancheri R, Tortori-Donati P. Spinal dysraphism: MR imaging rationale. Journal of Neuroradiology.Vol 31, N 1 january 2004, Tortoli-Donati P, Rossi A, Cama A. Spinal dysraphism: a review of neuroradiological features with embryological correlations and proposal for a new classification. Neuroradiology : Santiago Medina L. Spinal dysraphism: categroizing risk to optimize imaging. Pediatr. Radiol (Suppl 2): S242-S Demaerel Ph, Wilms G, Raaijmakers C, Verpoorten C, Casaer P, Plets C, Baert AL. MRI in spinal lumbosacral dysraphism. Eur. Radiol , Tortori-Donati P, Cama A, Rosa ML, Andreussi L, Taccone A. Occult spinal dysraphism: neuroradiological study. Neuroradiology : Tortori-Donati P, Rossi A, Biancheri R, Cama A. Magnetic resonance imaging of spinal dysraphism. Review.Top Magn Reson Imaging Dec; 12(6): Page 40 of 41

41 7.Rossi A, Biancheri R, Cama A, Piatelli G, Ravegnani M, Tortori-Donati P. Imaging in spine and spinal cord malformations. Review. Eur J Radiol May; 50(2): Rossi A, Gandolfo C, Morana G, Piatelli G, Ravegnani M, Consales A, Pavanello M, Cama A, Tortori-Donati P. Current classification and imaging of congenital spinal abnormalities. Semin Roentgenol Oct; 41 (4): Schenk JP, Herweh C, Günther P, Rohrschneider W, Zieger B, Tröger J. Imaging of congenital anomalies and variations of the caudal spine and back in neonates and small infants. Review. Eur J Radiol Apr; 58(1):3-14. Page 41 of 41