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King Edward Memorial Hospital Bombay, India
University of North Carolina School of Medicine Chapel Hill, NC
27599-7510
Diastematomyelia, or split spinal cord, is an uncommon congenital anomaly characterized pathologically by sagittal clefting of the spinal cord or filum terminale. This is usually caused by either a fibrous bony septum or an osteocartilaginous septum [1]. Diastematomyelia is believed to arise from adhesions between the embryonic ectoderm and endoderm. Intramedullary epidermoid cysts of the spinal cord are rare and are formed from epithelial tissue that becomes displaced during neural tube closure. We report a case of a 5-year-old girl with lumbar diastematomyelia and an intramedullary epidermoid cyst in the right hemicord.
A 5-year-old girl presented with a 2-month history of progressive weakness of her right leg and 4-year history of lower back pain. She also complained of dysesthesia over the lateral aspect of her right thigh. Neurologic examination revealed hyperactive reflexes of her right lower extremity and diminished response to fine touch and pressure. However, no definite sensory level was discerned. Motor examination indicated moderate paresis (strength, 2/5) of her right leg distally. An unsteady gait was noted. MR imaging of the spine was performed. MR studies revealed a dysraphic thoracolumbar spine with a low-lying cord. A cleft was seen in the spinal cord extending from T8 to L4 (Fig. 2A). Additionally, the right hemicord showed an intramedullary, ovoid, hypointense mass on T1-weighted images that was hyperintense on T2-weighted images, extending from T10 to T12 (Fig. 2B). In view of the absence of any calcification, a preoperative diagnosis of an epidermoid cyst was considered. Radical removal of the tumor, adhesiolysis of the fibrous septum, and decompression of the neural elements were performed. Microscopic examination of the sample revealed a cyst lined by stratified squamous epithelium with an outer layer of vascular connective tissue. A diagnosis of intramedullary epidermoid cyst was made. The postoperative course was uneventful and the patient's neurologic status gradually improved. By the second month, an almost complete recovery was characterized by significant return of muscle strength and relief from back and leg pain. To the best of our knowledge, she has been well for the last 2 years.
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Diastematomyelia is an uncommon congenital anomaly characterized pathologically by sagittal clefting of the spinal cord or filum terminale, with each half of the spinal cord being surrounded by a dural sac. This disorder is usually caused by either a fibrous bony septum or an osteocartilaginous septum [1]. Traditionally, two types of double-cord malformations are described: diastematomyelia and diplomyelia. In the latter process, the hemicords reside in separate dural sacs transfixed by a midline osteocartilaginous spur with each hemicord containing only lateral (no paramedian) roots. In their unified theory of embryogenesis, Pang et al. [2] proposed that both malformations result from a common ontogenetic error. Hypothetically, the error exists in the appearance of an accessory neurenteric canal through the midline embryonic disk that maintains communication between the yolk sac and amnion and thus enables contact between the ectoderm and endoderm within the canal. This abnormal fistulation causes regional splitting of the notochord. On the basis of common radiographic and surgical findings, these conditions are termed "split-cord malformations." One of two types is diagnosed, depending on the state of the dural tube and the nature of the median septum. In light of this nomenclature, the present case is a type I split-cord malformation.
Diastematomyelias are most frequently found in the lumbar spine, followed by the thoracic region. In a review of 45 cases by Russell et al. [3], 24 cases were noted to be in the lumbar region. Various precipitating factors have been implicated in their pathophysiology including trauma, spinal canal compression, and strong stretching factors. All these factors contribute to a neurologic deficit in an already compromised neural canal. Some form of an associated congenital anomaly, or dysraphism, of the vertebral column is a constant feature.
Intramedullary epidermoid tumors of the spinal cord are rare and are believed to arise from the displacement of ectodermally committed cells during neural groove closure between the third and fifth weeks of embryonic life [4]. Intraspinal epidermoid tumors represent fewer than 1% of all intraspinal tumors in adults [5]. Occasionally they may be traumatic in nature, acquired as a late complication of multiple lumbar punctures [6]. Intraspinal epidermoid cysts generally predominate in the lumbar region, but intramedullary epidermoids are more common in the thoracic region [4].
Epidermoid tumors of the spine have been associated with congenital malformations of the vertebral column including hemivertebrae, spinal teratomas, syringomyelia, and enterogenous cysts. Diastematomyelias have been associated with other congenital malformations such as syringomyelia, Chiari II malformations and, rarely, teratomas. Few reports of epidermoids with diastematomyelia are available. The presence of both diastematomyelia and epidermoid tumor in our patient further supports their embryologic basis of development and emphasizes the importance of early imaging for their diagnosis.
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  S. K. Mukherji Author's Correction Am. J. Roentgenol., March 1, 2001; 176(3): 815 - 815. [Full Text] [PDF]
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