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the congenital dermal sinus ( cds ) is a type of closed spinal dysraphism in which an epithelium - lined sinus tract from the dorsal skin surface extends inwards for a variable distance .
it occurs during neurulation when the neural groove closes to form the neural tube on day 26 of gestation and results from a failure of neuroectoderm to separate from the cutaneous ectoderm .
thoracic and cervical regions where the neural folds fuse first are the rare sites for dorsal dermal sinus , whereas lumbosacral and occipital dermal sinuses are relatively frequent .
dermoid and epidermoid tumors and posterior arch defects of the vertebral column can be seen in association of dorsal dermal sinuses .
the presence of dorsal dermal sinus in the upper thoracic region in association with spinal intramedullary dermoid cyst is rare .
a 2-year - old male child presented with a 3 month history of progressive lower limb weakness and urinary retention .
the patient 's skin over the upper thoracic region showed a midline dimple with hair [ figure 1 ] .
neurological examination revealed paraparesis ( 3/5 ) , exaggerated knee and ankle reflex , and sensory level at t6 .
plain x - ray of the thoracic spine was interpreted as normal . magnetic resonance imaging ( mri ) revealed a well - circumscribed intramedullary cystic mass extending from lower border of t4 to upper border of t7 and a sinus tract connecting it to the skin dimple [ figure 2 ] .
the tumor was hypointense on t1-weighted images and hyperintense on t2-weighted images with enhancement appreciated on gadolinium administration [ figure 3b ]
. clinical photograph of the patient 's skin over the upper thoracic region showing a midline dimple ( black circle ) magnetic resonance imaging of spine demonstrating a wellcircumscribed intramedullary cystic mass extending from lower border of t4 to upper border of t7 and a sinus tract connecting it to the skin surface .
the mass is hypointense on t1-weighted images ( a ) and hyperintense on t2-weighted images ( b ) magnetic resonance axial images of spine showing spina bifida of t6 vertebra ( a ) and contrast enhancement of the intramedullary mass ( b ) on operation , in prone position , vertical midline skin incision encircling the skin dimple was made , and the sinus tract was followed to the spinous process of t6 with the dissection of the dermal sinus stalk .
t6 spinous process was found to be splayed at the midline through which , the sinus tract traversed the lamina of t6 and then pierced the duramater .
a well - encapsulated , cystic , intramedullary tumor containing wax - like sebaceous materials and tuft of hair was encountered in communication with the sinus tract .
the surgical microscope made it possible to find a plane between the tumor and the spinal cord , and total excision was performed .
microscopic examination revealed a typical dermoid cyst lined by well - differentiated keratinizing squamous epithelium [ figure 4 ] .
photomicrograph of the excised mass revealing a typical dermoid cyst lined by well - differentiated keratinizing squamous epithelium ( original magnification , 50 )
cds results from defective separation of the cutaneous ectoderm from the neuroectoderm during the process of neurulation .
though they can occur at any level along the spinal axis , generally they occur at one end of the neural tube . in order of frequency , it is localized most frequently in the lumbosacral area ( 41% ) , followed by the thoracic ( 10% ) and cervical ( 1% ) areas .
the rarity of cds in the thoracic region seems to be related to neural tube closure .
fusion of the neural tube begins in the cervical region and then proceeds both cranially and caudally , closing at the cephalad extremity .
the areas of later closure of the neural tube have a higher incidence of dermal sinus .
dermoids are rare , benign , slow - growing lesions constituting 1.1% of intraspinal tumors .
the majority are in the extramedullary or subdural juxtamedullary in the lumbosacral region , usually in the conus or cauda equina .
the complex of upper thoracic cds beginning from the skin , passing through the tissue layers , communicating with the intradural intramedullary dermoid cyst and spina bifida observed in this patient is rare .
. this condition may be missed as a result of an asymptomatic clinical presentation . physical examination and mr imaging are helpful in the diagnosis .
the orifice of the sinus may be so small that it escapes detection except on close inspection .
the sinus tract begins at the skin dimple and tracks cephalad through the soft tissues to traverse the dorsal dura , as demonstrated in this case .
it becomes symptomatic as a result of either infection or associated mass lesions , which can be epidermoid , dermoid , or teratoma .
a progressively enlarging inclusion tumor along the sinus tract in the spinal canal will eventually result in compression of adjacent neural structures .
many inclusion tumors associated with cds are asymptomatic because of a slow growth rate , resulting in late presentation .
the majority of dermal sinuses clinically manifest within the 1 decade , usually before the age of 5 , because of their tendency to become infected .
aseptic meningitis may be observed because of pressure or rupture of a coexisting dermoid cyst and/or epidermoid tumors . in some patients , debris or purulent material
although it may be localized and superficial in form , it may also precede the onset of meningitis or intradural abscess .
therefore , the midline skin should be inspected carefully when a child suffers repeated episodes of unexplained meningitis .
morimoto et al . , reported cds in association with intramedullary abscess and dermoid at t12s1 level in a 1-month - old child who presented with a dimple over the lumbosacral junction discharging pus .
physical manifestations include typical skin lesions such as lipoma , hemangioma , hair follicles , dermal sinus mount , dimple , and meningocele .
mri provides rapid and accurate identification of the extent of these lesions , shows the extraspinal portion of the sinus tract and associated inclusion tumor , and defines the degree of the spinal cord compression .
the mr characteristics of dermoid cyst are hypointense on t1-weighted imaging , hyperintense on t2-weighted imaging , and peripheral enhancement with gadolinium administration .
once the diagnosis is made , treatment of cds is achieved by complete excision of the sinus tract , including removal of all intraspinal portions with any associated dermoid cysts .
intradural inclusion tumors are completely removed if possible . the tumor may be adherent to the neural element , but it is easily freed from the neural elements . in cases of ruptured or infected tumors , complete excision is nearly impossible owing to dense arachnoid adhesions . in such cases , it is not necessary to attempt removal of the scarred capsular wall entirely .
careful bipolar coagulation is likely to prevent recurrence and reduce the risk of neurological impairment .
therefore , prophylactic surgery is performed as early as possible , when the intervention will be easier and give a better outcome .
such dermal sinuses should be evaluated without delay , in view of the risk of infection and associated morbidity with an expanding inclusion tumor .
early diagnosis and prompt surgical intervention offer the best chance of functional neurological recovery and prevent serious morbidity .
dorsal dermal sinus is a rare , congenital lesion found most frequently in the lumbosacral followed by the occipital regions . 
 it is rarely localized at the thoracic level . 
 we report a rare case of thoracic congenital dermal sinus ( cds ) associated with an intramedullary dermoid cyst in a 2-year - old male child , who presented with a 3 month history of motor weakness of both the lower extremities . magnetic resonance imaging ( mri ) of spine showed an intramedullary dermoid cyst extending from the lower border of t4 to upper border of t7 , which was connected with the skin dimple along the sinus tract . 
 total excision of the dermoid cyst and the sinus tract with t57 laminectomy resulted in good functional recovery .