Infected lumbar dermoid cyst mimicking intramedullary spinal cord tumor: Observations and outcomes.

We report two unusual cases of a 17-month-old boy with a previously undiagnosed lumbar dermal sinus tract terminating in an intradural dermoid cyst and holocord edema or syrinx, presenting with paraparesis and sphincter dysfunction secondary to an intramedullary abscess and a 26-month-old boy with a previously undiagnosed lumbar dermal sinus tract terminating in an infected dermoid cyst and intramedullary abscess, presenting with recurrent episodes of meningitis and hydrocephalus. Pre-operative magnetic resonance imaging (MRI) studies in these patients were initially confused for an intramedullary spinal cord tumor; however, the presence of an associated dermal sinus tract made this diagnosis of neoplasm less likely. Total excision of the dermal sinus tract, debulking of the dermoid cyst and drainage of the intramedullary abscess through an L1-L5 osteoplastic laminoplasty and midline myelotomy, followed by long-term antibiotic therapy resulted in a good functional recovery. Post-operative MRI of the spine showed removal of the dermoid cyst, decreased inflammatory granulation tissue and resolution of the holocord edema or syrinx. We also performed a literature review to determine the cumulative experience of management of intramedullary abscess in this rare clinical setting.

Introduction

Most dermoid cysts are uncommon congenital non-neoplastic lesions that belong to occult dysraphic disorders. They are composed of a capsule containing epidermal elements and dermal derivatives.[1] Moreover, they are thought to originate from the totipotent ectodermal cells, which remain within the developing neural tube between the 3rd and 5th weeks of gestation. Dermoid cysts commonly co-exist with a dermal sinus tract in about half of cases. The dermoid cyst or dermal sinus tract can lead to neurological complications caused by tethering of the spinal cord or infection.[2] Although recurrent meningitis frequently occurs with dermal sinus tracts with or without dermoid cysts, intramedullary abscess is rare.[3456]

Dermoid cysts make up approximately 20% of intradural tumors in children in the 1st year of life.[7] A dermoid cyst is most frequently localized in the intradural compartment in the lumbar region of the spine. Although most dermoid cysts are congenital, some dermoid cysts are acquired and may develop after a lumbar puncture or injury.[8] A cyst may become symptomatic when it ruptures and chemical meningitis develops.[9]

Modern neuroradiological tools have made the diagnosis of intraspinal lesions more straightforward and allow for careful pre-operative planning. Dermoid cysts show various and heterogenous magnetic resonance imaging (MRI) intensity corresponding to the variable contents of the cyst, including fat tissue, keratin debris, hair, skin glands and their secretions and calcifications.[1] However, the presentation of an infected spinal dermoid cyst associated with intramedullary abscess and holocord edema or syrinx, poses a pre-operative diagnostic challenge. We present these cases of infected lumbar dermoid cyst and dermal sinus tract, for its notable location and exceptional radiologic findings.

Case Reports

Case 1

History and examination

The first case is about a 17-month-old boy with an unremarkable birth history who presented to our institution with a 3 month history of decreased oral intake, constipation and regression in developmental motor milestones. He refused to stand or walk and reverted to crawling. There was no history of fever. There were no recurrent bouts of meningitis. The family history is significant for a mother who had recent resection of an unspecified brain tumor.

On examination, the patient had good strength in his arms and legs. However, patellar and Achilles deep tendon reflexes were not able to be elicited. There was atrophy of his legs and he refused to bear weight with his lower extremities. There were no signs of myelopathy. Examination of the skin of his lower back showed a midline hyperpigmented macule with a palpable 0.5 cm diameter subcutaneous nodule. There was no visible dimple.

Imaging

Pre-operative MRI of the lumbosacral spine [Figure 1a and b] demonstrated a heterogenous enhancing intradural mass extending from L1 to S1. The mass demonstrated some septated fluid/cystic components. The conus medullaris and cauda equina could not be identified. There was diffuse edema and expansion of the adjacent spinal cord. Intramedullary spinal cord tumor was at the top of the radiological differential diagnosis.

Figure 1

(a) Pre-operative mid-sagittal short-tau inversion recovery and (b) contrast-enhanced T1-weighted lumbar spine MRI demonstrate a heterogenous enhancing intradural mass from L1 to S1 with some septated fluid/cystic elements. The cauda equina and conus medullaris cannot be identified. There is adjacent cord edema. In retrospect, a dorsal dermal sinus can be seen (arrow, b)

In retrospect however, a thin T1 hypointense band (dorsal dermal sinus) could be identified in the posterior lumbar subcutaneous fat extending obliquely toward the thecal sac at the lumbosacral junction. MRI of the cervical spine [Figure 2] showed holocord edema or syrinx up to the level of the medulla. Pre-operative MRI of the brain demonstrated ventriculomegaly. There were no enhancing lesions within the brain.

Figure 2

Pre-operative cervical T2-weighted mid-sagittal magnetic resonance imaging shows holocord edema or syrinx up to the level of the medulla

Operation

Prior to incision with the patient under general anesthesia and positioned prone on chest bolsters, we identified a small mid-lumbar skin dimple amidst the hemangiomatous skin lesion. We performed an elliptical incision to excise the hemangioma and follow a dermal sinus tract from the subcutaneous layer through a defect in the fascia and L5 lamina to its point of dural penetration. We then proceeded to perform an L1-L5 osteoplastic laminectomy in the standard manner.

Once the dura was opened, we observed that the dermal sinus tract terminated in an area of intense arachnoiditis and a bulbous mass that was not separable from the spinal cord or nerve roots. At this point, a diagnosis of dermal sinus tract associated with dermoid cyst was made. The mass was incised, cultures of its contents were taken and caseous material was expressed and resected. We were unable to perform a gross total resection of this dermoid cyst because of its adherence to nearby neural structures.

Pathology

The dermal sinus tract and the dermoid cyst specimens demonstrated dense fibroconnective tissue with florid xanthogranulomatous acute and chronic inflammation with foamy macrophages and foreign body giant cells. Very rare necrosis was noted. Scattered keratin squamous debris and rare hair shafts were present within the inflammation. These histologic findings were most consistent with a ruptured dermoid cyst. Cultures grew Klebsiella oxytoca and Pseudomonas. No evidence of malignancy was observed.

Post-operative course

The patient experienced transient urinary retention after surgery. The patient was kept in the hospital for 3 weeks of intravenous (IV) antibiotics. His urinary retention and constipation had resolved at the time of discharge. Moreover, just prior to discharge, the patient was ambulating with an assistive device. At 9 months after surgery, the patient continues to do well and remains neurologically stable.

Case 2

A 26-month-old boy with a normal birth history was admitted to our pediatric intensive care unit with fever, neck stiffness, vomiting, lethargy and difficulty bearing weight. His past medical history is significant for at least three episodes of meningitis over the past year, multiple scattered cerebral infarctions, right supraclinoid internal carotid artery stenosis and progressive ventriculomegaly. The patient had normal development until the first episode of meningitis 1-year-ago; since then, he has had a steady decline. A lumbar puncture as part of a work-up for another bout of meningitis was attempted; however, it was a “dry tap.”

On examination, the patient had good strength in his arms and legs spontaneously. He was hyperreflexic throughout. He had upgoing toes on Babinski response bilaterally. Examination of the skin of his lower back showed a small scab in the area of his prior lumbar puncture. There was no obvious dimple. There were no other unusual cutaneous stigmata.

Pre-operative MRI of the lumbosacral spine [Figure 3a and b] demonstrated a heterogenous thick rim-enhancing intradural mass extending from L1 to S1. The mass demonstrated multi-septated fluid/cystic components. This mass filled and expanded the thecal sac with widening of the distal thoracic and lumbar bony spinal canal. The conus medullaris and cauda equina could not be identified. There was expansion and T2-hyperintense signal from T4 along the caudal length of the spinal cord [Figure 4].

Figure 3

(a) Pre-operative mid-sagittal contrast-enhanced T1-weighted lumbar spine magnetic resonance imaging demonstrates a heterogenous thick rim-enhancing intradural mass from L1 to S1 with multi-septated fluid/cystic components. The cauda equina and conus medullaris cannot be identified. (b) A dorsal dermal sinus tract (arrow) can be seen on sagittal T2-weighted images

Figure 4

Pre-operative thoracic T2-weighted mid-sagittal magnetic resonance imaging shows T2-hyperintensity extending from T4 along the remaining caudal length of the spinal cord

Most importantly with experience gained from our previous case, close attention was paid to radiographic features of occult spinal dysraphism. Indeed, there was a dorsal dermal sinus tract identified at the lumbosacral junction with communication from the skin at L5 to the intrathecal contents just below the S1 posterior elements. Pre-operative MRI of the brain demonstrated ventriculomegaly with transependymal flow. There were no enhancing lesions within the brain.

Due to signs of increased intracranial pressure, an external ventricular drain was placed before addressing the spinal pathology. The opening pressure was moderately high at 20 cm of water. We then positioned the patient prone on chest bolsters. Prior to incision, we identified a small lower lumbar skin dimple underneath scab. We performed an elliptical incision to excise the dimple and follow a dermal sinus tract from the subcutaneous layer through a defect in the fascia and S1 lamina to its point of dural penetration. We then proceeded to perform an L1-L5 laminectomy in the standard manner.

Once the dura was opened, pus was encountered and cultured. We found that the dermal sinus tract terminated in a dermoid cyst densely adherent to the spinal cord or nerve roots. At this point, a diagnosis of dermal sinus tract associated with dermoid cyst was confirmed. The dermoid cyst was incised and cheese-like material was expressed and resected. We performed a partial resection of the dermoid cyst.

The histologic findings were consistent with a dermal sinus tract associated with a ruptured dermoid cyst. Cultures grew Enterococcus faecalis and Escherichia coli. No evidence of malignancy was observed.

The patient was unable to be weaned from the external ventricular drain. He subsequently underwent ventriculoperitoneal shunt placement. The patient was kept in the hospital for 3 weeks of IV antibiotics. At the time of discharge, he was walking independently and had normal bowel and bladder function. At 6 months after surgery, the patient continues to do well although he remains developmentally delayed. Follow-up MRI shows partial decompression of the dermoid cyst, interval resolution of syrinx and improved spinal cord edema [Figure 5a and b].

Figure 5

Post-operative T2-weighted mid-sagittal magnetic resonance imaging of the (a) thoracic and (b) lumbar spine at 6 months after surgery shows partial decompression of the dermoid cyst with residual dermoid cyst centered at the L4-5 level. There is interval resolution of the syrinx and improved edema of the spinal cord

Discussion

Spinal dermal sinus tracts may cause cutaneous abscess, meningitis, or intraspinal abscess by a contiguous route for transmission of bacteria. Approximately half of all dermal sinus tracts have associated dermoid or epidermoid cysts, at the end of the tract, which may cause symptoms of spinal cord or root compression. Dermoid cysts are uncommon benign maldevelopmental lesions that can occur anywhere along the neuraxis. These are considered to be the end product of a defective closure of the neural tube occurring between the 3rd and 5th weeks of gestation.[10] Dermoid cysts originate from trapped fragments of the primitive ectodermal layer and mesenchymal elements within the closing neuroectodermal folds. This explains their predilection for midline localization.

Intramedullary abscess of the spinal cord is a rare complication of a dermal sinus tract. Contiguous spread of infection via a spinal dermal sinus tract may represent a plausible mechanism leading to the development of intramedullary abscess in children.[345611] Medical treatment alone, consisting of long-term antibiotics may be tried in selected cases.[312] The majority of authors, however, recommend neurosurgical intervention consisting of excision of the dermal sinus tract and dermoid cyst together with the drainage of pus by means of limited laminectomy and myelotomy[5611121314] [Table 1]. It is unclear whether complete resection of the dermoid cyst offers an advantage over partial resection in improved long-term outcome. Complete resection of a ruptured infected dermoid cyst may be treacherous as it is likely densely adherent to surrounding nerve roots and spinal cord.

Table 1

Patient demographics and clinical and operative data in 6 children with infected dermoid cysts associated with intramedullary abscesses

Few cases of intramedullary abscess secondary to infected dermoid cyst and related holocord edema or syrinx have been reported.[61415] Neurological deficits in these patients have ranged from tetraparesis to paraparesis, as in our patients. The pathomechanism of the holocord edema or syrinx is unclear. Inflammation, infection and associated venous congestion within the spinal canal may be an underlying etiology.[3] Likewise, widespread arachnoiditis from both infection and chemical meningitis and obstruction of the central canal or other alterations of CSF circulation, as in intramedullary spinal cord tumors, may represent another cause.

There are three major MRI characteristics for presumptive diagnosis of intramedullary spinal cord tumors: Expansion of the spinal cord; the presence of nodular contrast enhancement; and formation of cystic elements.[16171819] These same radiologic features of intramedullary spinal cord tumors are shared with our case: Spinal cord expansion from the intramedullary abscess and holocord edema or syrinx; thick nodular enhancement of the abscess capsule; and cystic formation from the necrotic epicenter of the abscess and holocord syrinx. However, the presence of a concurrent dermal sinus tract on pre-operative imaging was more consistent with infected or ruptured dermal cyst.

Prognosis varies depending on the pre-operative status of the patient with dermal sinus tract and spinal dermoid cyst. Results are excellent for non-infected asymptomatic cases.[6] On the contrary, a complete recovery in patients with progression to intramedullary abscess is achieved in only 20% of cases.[346]

Conclusions

We present two unusual cases of children with intramedullary abscess and holocord edema secondary to an infected lumbar dermoid cyst presenting with paraparesis and regression of developmental milestones. The constellation of radiographic findings mimicked that of an intramedullary spinal cord tumor with syrinx. The pathomechanism for the holocord edema or syrinx is not clearly elucidated. Like most authors, we recommend prompt surgical treatment including the resection of the dermal sinus tract and dermoid cyst and drainage of the intramedullary abscess.