Thoracic congenital dermal sinus associated with intramedullary spinal dermoid cyst.

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 T5-7 laminectomy resulted in good functional recovery.

Introduction

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.[1] 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.

Case Report

A 2-year-old male child presented with a 3 month history of progressive lower limb weakness and urinary retention. He had a skin dimple, which was identified at birth. Subsequent observations of intermittent sebaceous discharge were not followed by medical examinations. There was no history of meningitis. On physical examination, 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]. Spina bifida of T6 was evident on axial images [Figure 3a]. The tumor was hypointense on T1-weighted images and hyperintense on T2-weighted images with enhancement appreciated on gadolinium administration [Figure 3b].

Figure 1

Clinical photograph of the patient's skin over the upper thoracic region showing a midline dimple (black circle)

Figure 2

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)

Figure 3

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. T5–7 laminectomy was performed, and the dura was opened. 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. The dura was closed in a water-tight fashion. Microscopic examination revealed a typical dermoid cyst lined by well-differentiated keratinizing squamous epithelium [Figure 4]. The postoperative course was uneventful, with notable improvement in neurological function. The patient gradually regained normal strength in his leg in 6 months time.

Figure 4

Photomicrograph of the excised mass revealing a typical dermoid cyst lined by well-differentiated keratinizing squamous epithelium (original magnification, ×50)

Discussion

Verebely first described dermal sinus in 1913. Walker and Bucy first used the term “congenital dermal sinus” in 1934.[2] CDS results from defective separation of the cutaneous ectoderm from the neuroectoderm during the process of neurulation.[13] 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.[1456] Wang et al.,[1] stated that they observed thoracic CDS quite rarely. 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.[7]

Dermoids are rare, benign, slow-growing lesions constituting 1.1% of intraspinal tumors.[8] The majority are in the extramedullary or subdural juxtamedullary in the lumbosacral region, usually in the conus or cauda equina.[8] Intraspinal intramedullary dermoid cyst is uncommon.[9] 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. Out of five cases of spinal CDS described by Wang et al.,[1] one had dermoid cyst at T6–T7 level in association with CDS. This condition may be missed as a result of an asymptomatic clinical presentation. Physical examination and MR imaging are helpful in the diagnosis.

The hallmark of CDS is a midline cutaneous dimple overlying the spine. Other cutaneous abnormalities, such as hemangiomas or hairy patches may be associated. The orifice of the sinus may be so small that it escapes detection except on close inspection. Hair may be seen protruding from the opening. 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.

Congenital thoracic spinal dermal sinus presents clinically with recurrent meningitis and neural compression. 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 1st decade, usually before the age of 5, because of their tendency to become infected.[7] Aseptic meningitis may be observed because of pressure or rupture of a coexisting dermoid cyst and/or epidermoid tumors.[510] In some patients, debris or purulent material may drain from the sinus tract, as in this patient. Although it may be localized and superficial in form, it may also precede the onset of meningitis or intradural abscess. Skin stigmata and recurrent meningitis of unknown origin are important clues. Therefore, the midline skin should be inspected carefully when a child suffers repeated episodes of unexplained meningitis.[111] Morimoto et al.,[12] reported CDS in association with intramedullary abscess and dermoid at T12–S1 level in a 1-month-old child who presented with a dimple over the lumbosacral junction discharging pus.

Diagnosis in cases of dermal sinus is made based on physical and neuroimaging examinations. Physical manifestations include typical skin lesions such as lipoma, hemangioma, hair follicles, dermal sinus mount, dimple, and meningocele.[11] Neuroimaging examinations include direct X-ray films, computerized tomography, and MRI. The sinus tract is best demonstrated by MRI.[41113] 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.[45671011] 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. Broad spectrum antibiotic prophylaxis should be used even when no infection is detected. Cultures should be obtained when symptoms of infection occur.[613]

Conclusion

CDS associated with an intramedullary dermoid cyst in the thoracic spinal level is rare. 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.