Congenital dermal sinus in mid-dorsal spine with large intramedullary dermoid cyst in an 18-months-old child.

Intramedullary dermoid cyst is a rare entity. It is usually associated with spinal dysraphism and dermal sinus. Our case is an 18-months-old female child who presented with history of fever and mild difficulty in moving left leg. She had a sinus in mid dorsal spine since birth with history of intermittent discharge from it. On magnetic resonance imaging of spine she was diagnosed to have large intramedullary epidermoid/dermoid cyst in the D2-7 vertebral level with a sinus tract. A dermoid cyst along with the sinus tract was excised. Post-operative follow up period was uneventful with full recovery.

Introduction

The incidence of intramedullary tumors of the spinal cord is 2-4% of all central nervous system tumors.[1] Intraspinal dermoid cysts are less than 1% in incidence, commonly seen in extradural location in lumbar area. They are usually associated with either lumbar spinal dysraphism or a dermal sinus tract.[2] Intramedullary dermoid cyst is extremely rare and only a few cases were reported. They present usually very late with significant neurological compromise. We report a case of large intramedullary dermoid cyst of the spinal cord associated with a dermal sinus in mid-dorsal-spine in an 18-months-old female child presenting early with fever due to intermittent sinus discharge and infection.

Case Report

An eighteen-months-old female child presented with history of mild fever and intermittent discharge from a sinus in the mid-dorsal area. On examination, she was febrile with normal power and sensation in all limbs except mild stiffness of left leg. Posterior aspect of mid-dorsal spine (D5) shows a skin dimple with no active discharge at presentation [Figure 1]. Magnetic resonance imaging (MRI) of whole spine revealed a large intramedullary cystic lesion in the dorsal segment of spinal cord extending from D2 to D7 vertebral level with single posterior sinus tract opening to skin at D5 vertebral level. The cystic lesion shows T1-weighted (T1W) hypointense, T2-weighted (T2W) and short tau inversion recovery (STIR) hyperintense signal, restricted diffusion in diffusion-weighted image (DWI) and apparent diffusion coefficient (ADC) image. Small T1W isointense and T2W hypointense content noted inside the cystic lesion. No fat signal was seen inside the mass. Post-contrast MRI image shows no enhancement of the lesion [Figure 2]. Intramedullary spinal epidermoid/dermoid with posterior sinus tract was given as possible radiological differential.

Figure 1

The child shows dermal sinus tract opening to skin as skin dimple over the posterior aspect of dorsal spine in midline

Figure 2

Intramedullary cystic lesion of spinal cord extends from D2 to D7 vertebral level and shows T1W hypointense (a), T2W hyperintense (b), STIR hyperintense signal (c), non-enhancement in post-contrast image (d and e) and restriction of diffusion in DWI (f) and ADC (g) sequence. The dermal sinus track is seen as hypointense linear structure in T2W and STIR image (b and c)

Dorsal D1 to D8 laminectomy was done. Mid-line myelotomy and total tumor excision under microscope was done. Injection methyl prednisolone was given as bolus dose (30 mg/kg body weight) during intra operative period and continued for 24 hour in post-operative period with a dose of 5.4 mg/kg body weight. Tuft of hair and cheesy material with a thin capsule were removed in piece meal; portion of the capsule could not be removed as it was densely adhered to the cord. Dermal sinus tract was ending within the dermoid capsule [Figure 3] and was also excised. Myelotomy was left open and water tight dural closure was done. Post operatively she developed mild weakness of left lower limb (grade-IV power) which she recovered by 10th post-operative day. She was discharged free of neurological deficit.

Figure 3

Intraoperative picture shows the dermal sinus merging to the intramedullary dermoid

The histopathological diagnosis of the lesion confirmed dermoid cyst [Figure 4].

Figure 4

Microphotograph showing the cyst lined by squamous epithelium containing keratinous flakes in the lumen; and the wall shows dermal appendages, adipocytes and nerve bundles which confirmed it as dermoid cyst

Discussion

Dermal sinus is an epithelium-lined track, which extends inward from the skin surface for varying distances and often connects the body surface with the central nervous system or its coverings. It results due to focal area of incomplete disjunction of cutaneous ectoderm from neural ectoderm during the process of neurulation. The dermal sinuses are commonly seen in lumbosacral and occipital regions.[1] The patients become symptomatic due to infection or because of compression of neural structures by an associated dermoid or epidermoid tumor.[2] Acute worsening of neurological deficit may be seen due to spontaneous rupture of dermoid cyst resulting in ventriculitis and meningitis.[3] Dermal sinuses in midline are commonly associated with a dermoid cyst and those in paramedian location with epidermoid cyst.[45] Dermoid cyst constitute less than 1% of congenital spinal tumor.[46] Dermoids are most frequently seen in dorsolumbar area (75%) out of which 63% are in intradural extramedullary location and 38% in intramedullary location.[26] Dermoid cyst is thought to arise from inclusion of embryological ectodermal rest cell in neural epithelium during neural tube closure in 3rd to 5th week of gestational age.[78]

Intramedullary dermoid cyst usually presents late in 2nd or 3rd decade of life with significant neurological compromise. In presence of a dermal sinus, presentation becomes early due to sinus discharge and infection.[23]

The appearance of dermoid cyst on MRI is variable, sometimes showing high signal intensity on T1-weighted images (T1W), but more commonly having low to intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images (T2W). The lack of a fatty signal may be a result of secretions from sweat glands within the tumor causing increased water content. Dermoid shows diffusion restriction and no post-contrast enhancement unless they are infected like epidermoid. Infection is more common in association with sinus track. T1-weighted images with wide window settings best show the sub-cutaneous portion of the sinus tracts, whereas T2-weighted images show the sinus tract as a hypointense linear or curvilinear structure.[9] In our case the dermoid shows predominant T1 hypointense, T2W/STIR heterogeneously hyperintense signal and diffusion restriction with T2W hypointense sinus track.

The common differential diagnosis of intramedullary cystic lesions is arachnoid cyst and epidermoid cyst. The arachnoid cyst shows cerebrospinal fluid (CSF) signal with no diffusion restriction whereas epidermoid shows hyperintense signal in fluid attenuation recovery sequence and restriction of diffusion.[9]

Total microsurgical excision of dermoid cyst along with the capsule is the treatment of choice. Partial excision of dermoid cyst wall with decompression in case of dense adhesion of lesion with spinal cord also gives good clinical outcome.[10] In our case, the whole of the dermoid cyst along with the sinus tract was excised except small portion of capsule which was attached firmly to the spinal cord.

Conclusion

Dermal sinus in mid-dorsal spine associated with a large intramedullary dermoid cyst presenting only with intermittent fever, sinus discharge and subtle neurological deficit are rare. Patient with dermal sinus should be evaluated early with spinal imaging preferably by MRI of spine to rule out underlying spinal cord lesion which will facilitate better treatment at the early stage of disease, thus preventing development of neurological deficit.