Infected dermoid tumor causing tethered cord after myelomeningocele repair.

Intramedulary dermoid tumors are rare tumors mostly found associated with dermal sinus tracts. Spinal dermoid tumor can occur after myelomeningocele repair. Infected dermoid tumors are reported in patients with dermal sinus tracts as well, but have never been reported subsequent to myelomeningocele surgery. Here, we report a rare association of infected dermoid tumor with tethered cord without dermal sinus tract in a child who had been operated for myelomeningocele during infancy.

Introduction

Progressive neurologic deterioration or back and leg pain in children with a history of Myelomeningocele (MMC) surgery may be due to cord tethering or growth of an intradural inclusion tumor. Symptomatic tethered cord develops in 10–13% of children with MMC.[12] Loss of motor function in the lower extremities, gait abnormality, back or leg pain, scoliosis, and foot deformity are common findings in postsurgical tethering. Infrequently, these symptoms are caused by dermoid tumors (1.5%).[2]

Here, we report a child who developed progressive neurological deterioration and severe back and leg pain subsequent to large infected dermoid tumor extending underneath the skin to the spinal canal and intramedullary area.

Case Report

A 3-year-old boy was referred to neurosurgical department because of severe back and leg pain and motor regression. He was a known case of lumbar MMC and was operated at 8 months of age. He was shunted for progressive hydrocephalus 3 weeks later. He could sit at 11 months of age and stand at age of 2 years on his knees, but could not move the distal part of his legs at all. His back pain had started 3 months ago, which was severe at night and made him unable to sit. Subsequently, he experienced severe leg pain, which prevented him from moving the proximal part of his lower extremities and his mother faced difficulty while cleaning him after urination or defecation.

On physical examination, the child was afebrile, but very irritable, with good mental performance, and normal neurological examination of upper limbs. Both lower extremities had lost any movement in proximal and distal parts (0/5). Deep tendon reflexes were absent in both legs. Sensory level was undetectable because of the child's uncooperation. He was incontinent for urine and feces. A small tender bulging was identified in his back under the MMC repair incision for one week before admission, but no dermal sinus was found inside or around the incision. Spinal Magnetic Resonance Imaging (MRI) was performed one month before surgery, which revealed cord tethering (cord at L4- L5level). Distal cord was attached to a mass, which was isointense in T1- and hypointense in T2-weighted images. It was extending from distal cord through the bony defect to the extraspinal canal space. The cord was dilated from the level of tethering to L1level with a lesion, which was isointense to hypointense in T1- and hyperintense in T2-weighted images, dissimilar to the intensity of cerebrospinal fluid [Figures 1 and 2].

Figure 1

Isointense mass in T1-weighted image attached to the cord causing tethered cord. Notice the hypointense signal inside the expanded cord compatible with infected dermoid tumor found during surgery

Figure 2

Hypointense mass in T2-weighted image is extending from distal cord through the bone defect to the extraspinal canal space and the prior MMC surgery field

The child underwent surgery with the suspicion of tethered cord associated with an inclusion tumor. In the prone position, the prior midline vertical incision was opened. During the dissection of subcutaneous tissue, fine hairs and white yellow creamy collection were drained spontaneously with high pressure. This lesion was extending through the previous spinal posterior element defect into the cord. Dura mater, cord and dermoid tumor were attached to each other at the depth of previous surgical field, and the tumor was extending from the extraspinal area to the intramedullary space between L4 and L1 vertebral levels. Access to the whole lesion was possible with osteoplastic laminotomy of L1 to L4. Dura mater was severely tense at the level of L2-L4. Microsurgical release of all intradural adhesions was performed to achieve circumferential untethering of spinal cord associated with gross total resection of intramedullary mass. Complete excision of the dermoid cyst and capsule were performed, which was followed by primary closure of the dura. On histopathological examination, specimen had the characteristic features of a dermoid cyst, with simple squamous epithelium, hair follicles, and cholesterol-containing debris. The material was sent for culture, which was positive for Klebsiella. The postoperative period was unremarkable. He underwent intravenous antibiotics therapy with cefotaxime and amikacin for 4 weeks. The pain recovered postoperatively. He could move proximal part of his lower extremities with score of 1-2/5, but was unable to stand on his knee as he could do before. His sphincter problem remained unchanged.

Discussion

Children with MMC are born with a wide range of neurological deficits that will remain after primary repair of lesion. Any new changes in the previous neurological, urological or orthopedics status warrant an extensive investigation to rule out the possible causes, especially tethered cord syndrome.

Tethered cord is a common complication following MMC surgery, which may be found in most patients when they are evaluated with spinal MRI, but symptomatic tethering occurs only in 10-30% of them.[34] Tethered cord may present with subtle changes in prior neurophysical situation, which become progressive and disabling if neglected. Spinal cord tethering due to dermoid cyst subsequent to MMC surgery has been reported so far, which can occur decades after closure.[5-8] All patients with symptomatic tethered cord have attachment of spinal cord to the prior closure site, which can be associated with inclusion tumors in 16% of instances.[9]

Dermoid tumors following MMC surgery may result from inadequate excision of dermal elements during dissection of placode or dura mater from the skin or with implantation of dermal elements inside the repair site.[310] The growth of the entrapped skin may predispose the development of dermoid tumor. Alternatively, this tumor can be an associated abnormality with MMC, which was undiagnosed or neglected because of very small size at the time of primary repair, especially during surgery without magnification. Cases of dermoid tumor in MMC children who were operated during the intrauterine period have been reported, suggesting a higher potential for rapid growth of this tumor in lesions that were closed in utero rather than after birth.[10]

Dermal sinus tract as a rare congenital abnormality is accompanied by inclusion tumors in 43% of instances, wherein most tumors are dermoids.[1112] Infected dermoid tumor or spinal abscess has been observed with dermal sinus tract.[13] Intramedullary spinal abscess without sinus tract is extremely rare, but a devastating condition in children.[12-16] Intramedullary abscess and dermoid tumor without dermal sinus have been reported before;[5] however, not following MMC repair and especially not associated with tethered cord.

In order to explain infected dermoid tumor in this patient with prior MMC repair, we propose several explanations. Implantation of bacteria during closure of MMC sac can lead to abscess formation but occurence three years after the first surgery seems to be unusual. Microscopic sinus tract through the preceding MMC surgery incision can be a way for bacteria to reach the subcutaneous space. Hematogenous superinfection of the dermoid cyst during repeated urinary tract infections in MMC patient is another possiblity for abscess formation in this case.

Dermoid tumors, even infrequent, should be considered in the differential diagnosis of the causes of neurological deterioration in patients with a history of MMC repair. Along with tethered cord syndrome, dermoid tumor can complicate the prior neurological and physical status of the child, and should be searched vigilantly during evaluation of these patients. Because of rapid growth of dermoid tumors and associated infection, these can deteriorate the previous neurological status in a more aggressive and destructive manner as compared to tethered cord per se. Awareness of such pathology in patients with previous history of myelomeningocele repair, early diagnosis and surgical intervention can provide better result with less disability.

Conclusion

Tethered cord syndrome should be investigated in any patient with a history of MMC repair if one finds neurological, orthopedics, or urological deterioration. Dermoid tumor is considered as an important differential diagnosis during thorough evaluation of the causes of worsening. In order to minimize the risk of dermoid tumor development following MMC surgery, any residual epidermal or dermal elements should be resected from the neural placode. The operative field should be explored accurately proximal and distal to the sac to find any associated anomaly or minute inclusion tumor and prevent late inclusion tumor formation and tethered cord.