Indian Journal of Radiology Indian Journal of Radiology  

   Login   | Users online: 1655

Home Bookmark this page Print this page Email this page Small font sizeDefault font size Increase font size     

 

MUSCULOSKELETAL Table of Contents   
Year : 2003  |  Volume : 13  |  Issue : 1  |  Page : 67-74
Pictorial essay : MRI findings in occult spinal dysraphism


Department of Radiology, Amrita Institute of Medical Sciences, Amrita Lane, Elamakkara, Cochin-682026, Kerala, India

Click here for correspondence address and email
 

Keywords: Spinal Dysraphism, Diastomatomyelia, Neurenteric Cyst

How to cite this article:
Moorthy S, Sreekumar K P, Prabhu N K. Pictorial essay : MRI findings in occult spinal dysraphism. Indian J Radiol Imaging 2003;13:67-74

How to cite this URL:
Moorthy S, Sreekumar K P, Prabhu N K. Pictorial essay : MRI findings in occult spinal dysraphism. Indian J Radiol Imaging [serial online] 2003 [cited 2019 Nov 22];13:67-74. Available from: http://www.ijri.org/text.asp?2003/13/1/67/28630

   Introduction Top


Congenital spinal anomalies have been classified into three broad categories - 1) Open spinal dysraphism 2) Occult spinal dysraphism and 3) Caudal spinal anomalies. Occult spinal dysraphism refers to a heterogenous group of disorders in which the neural tissue lies deep to an intact skin cover. Open dysraphism is characterised by exposed neural tissue and the condition is clinically evident at birth. In caudal spinal anomalies, the clinical picture is dominated by anorectal, urogenital and lower limb anomalies [1]. Occult spinal dysraphisms, tend to be overlooked at birth. The manifestations become apparent later in life due to either cutaneous stigmata or slowly progressing neurological signs [2]. Imaging is essential to diagnose and characterize these lesions. The purpose of this article is to review the MR findings in various conditions which have been classified under occult spinal dysraphism.

Embryology

By the 17th post-ovulation day, the notochord forms in the midline of the embryo. The ectoderm overlying the notochord is induced to form the neuroectoderm. The neuroectoderm folds and dissociates from the superficial ectoderm in a process termed primary neurulation. This process explains the formation of most of the spinal cord. The distal conus and the filum terminale develop as a result of canalization and retrogressive differentiation or secondary neurulation.

I) Defects of Primary and Secondary Neurulation

1) Lipoma

Lipoma is the most common type of occult spinal dysraphism. Spinal lipomas are more common in females. In infancy, the presentation is usually as a mass in the back. Later in life, pain, motor deficits, urinary incontinence and foot deformities are common presenting features [1],[3].

A classification based strictly on the embryology divides lipomas into dorsal lipoma, transitional lipoma and terminal lipoma [4]. Both dorsal and transitional lipomas have an intraspinal component which blends with the cord and a fibro-fatty stalk that fuses with the subcutaneous fat. In dorsal lipomas, however, the cord distal to the attachment of lipoma is entirely normal [Figure - 1]. These are considered as defects of primary neurulation and constitute less than 10% of all spinal lipomas. If the superficial ectoderm separates from the neuroectoderm before the neural tube has completely closed (premature disjunction), then the mesoderm comes into contact with interior of the neural tube. This would prevent complete closure of the neural tube. The mesoderm in contact with the interior of the neural tube is induced to form fat [1]. In transitional lipomas, the distal cord and conus terminate in the lipoma and there is no normal cord caudal to the lipoma. Since the distal conus is derived from a process of secondary rather than primary neurulation, defects of both processes have to be postulated to explain the condition - hence the term `transitional`. The common lumbosacral lipomyelomeningocoele is a transitional lipoma [Figure - 2]. A defective process of canalisation and retrogressive differentiation alone results in a terminal lipoma represented by lipomas of the filum terminale [Figure - 3].

Intradural or spinal cord lipomas are, probably, a rare form of dorsal lipoma, comprising approximately 4% of all spinal lipomas and 1% of all spinal cord tumours. Spina bifida is usually absent or small, if present. These lipomas are most commonly seen in the cervico-thoracic region [Figure - 4].

2) Tight filum syndrome

Tight filum syndrome represents a failure of retrogressive differentiation and is part of the same pathogenetic continum as filar lipoma. The filum should measure more than 2 mm in thickness there should be no other cause for tethering. Conus medullaris is elongated with no sharp transition between the conus and filum. Almost all patients have a spina bifida. The tethered cord may terminate in a lipoma [1],[3] [Figure - 5].

3) Terminal syringohydromyelia

Expansion and cephalic extension of the terminal ventricle within the distal conus can occur involving the distal one thirds of the cord [Figure - 6]. This can be seen in upto 30% of patients with occult spinal dysraphism or can occur alone [5].

4) Dorsal Dermal sinus

During the process of primary neurulation, the neuroectoderm may fail to separate from the superficial ectoderm at one point (non-disjunction), as development proceeds this adhesion gets drawn out into an epithelial lined tube connecting the spinal cord to the skin of the back. This epithelial track is termed dorsal dermal sinus [1]. The lumbosacral region is the commonest location. The sinus tract may end superficial to the dura, but in more than 50% of cases it extends into the spinal canal. In 60% of cases the tract incorporates or ends in an epidermoid or dermoid [1] [Figure - 7][Figure - 8]. CSF leak through the sinus tract, is rare, and can lead to meningitis [1] [Figure - 9].

Almost 50% of spinal epidermoids and dermoids occur without an associated spina bifida or dermal sinus [Figure - 10]. An inadvertent inclusion of cutaneous ectoderm during neural tube closure is thought to result in these isolated lesions.

II) Split notochord and related disorders

These conditions result from a persistant adhesion between the entoderm and the ectoderm in the midline which interferes with the normal formation of the notochord. The notochord is bisected and thereby inducing the formation of two hemicords.

1) Diastomatomyelia

More than 80% of cases are seen in females. Presentation is typically with orthopaedic deformities like clubfoot. Segmentation anomalies of the vertebrae like hemivertebrae, butterfly vertebrae and block vertebrae are seen in most patients. The spinal cord is split sagittally into two halves by a fibrous or osteocartilagenous septum. The conus lies low and is tethered. Two distinct types of diastomatomyelia have been described. In slightly less than 50% cases, each hemicord lies within its own dural tube and in nearly all these cases, there is a bony septum [Figure - 11]. In the rest, the two hemicords lie within a single dural tube. In these patients there will not be a bony spur [1],[3] [Figure - 12].

2) Neurenteric cyst

These are cysts, which have a definite connection with the spinal cord and vertebra and are lined with alimentary tract mucosa. The cyst may be extraspinal, in the posterior mediastinum, with an intraspinal component that invaginates the cord. An anterior or posterior spina bifida is usually associated [Figure - 13]. The cyst may also be entirely intraspinal without any spina bifida [1],[7].

 
   References Top

1.Naidich TP, Zimmerman RA, McLone DG, Raybaud CA, Altman NR and Braffman BH. Congenital anomalies of the spine and spinal cord. In: Atlas SW ed Magnetic resonance imaging of the brain and spine, 2nd ed. Philadelphia: Lippincott-Raven, 1996: 1265-1337  Back to cited text no. 1    
2.McLone DG, Thompson D. Lipomas of the spine. In: McLone DG ed Pediatric Neurosurgery. Philadelphia: WB Saunders, 2001: 289-301  Back to cited text no. 2    
3.Pang D. Tethered cord syndrome. In: Wilkins RH and Rengachary SS eds Neurosurgery, 2nd ed. New York: McGraw-Hill, 1996: 3465-3496  Back to cited text no. 3    
4.Chapman PH. Congenital intraspinal lipomas: anatomic considerations and surgical treatment. Childs Brain 1982; 9: 37-47.  Back to cited text no. 4  [PUBMED]  
5.Fujiwara F, Tamaki N, Nagashima T et al : Intradural spinal lipomas not associated with spinal dyraphism: a report of four cases. Neurosurgery 1995; 37:1212-1215.  Back to cited text no. 5    
6.Iskander BJ, Oakes WJ, McLaughlin C, Osumi ALK, Tein RD. Terminal syringohydromyelia and occult spinal dysraphism. J Neurosurg 1994; 81:513-519.  Back to cited text no. 6    
7.Wilkins RH. Intraspinal cysts. In: Neurosurgery Wilkins RH and Rengachary SS eds 2nd ed . New York: McGraw-Hill, 1996: 3509-3519.  Back to cited text no. 7  [PUBMED]  

Top
Correspondence Address:
S Moorthy
Department of Radiology, Amrita Institute of Medical Sciences, Amrita Lane, Elamakkara, Cochin-682026, Kerala
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


Rights and PermissionsRights and Permissions


    Figures

[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9], [Figure - 10], [Figure - 11], [Figure - 12], [Figure - 13]

This article has been cited by
1 Spinal dysraphism: A review of clinical manifestations and surgical treatment options
Sweet, J., Kalhorn, C.G.
Seminars in Spine Surgery. 2005; 17(1): 23-29
[Pubmed]



 

Top
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Email Alert *
    Add to My List *
* Registration required (free)  


    Introduction
    References
    Article Figures

 Article Access Statistics
    Viewed15953    
    Printed623    
    Emailed19    
    PDF Downloaded0    
    Comments [Add]    
    Cited by others 1    

Recommend this journal