A rare case of giant terminal lipomyelocystocele with partial sacral agenesis.

Terminal myelocystoceles (TMCs) are a rare form of occult spinal dysraphism. They constitute approximately 5% of skin covered lumbosacral masses. The TMC is composed of a low-lying conus medullaris with cystic dilatation of caudal central canal, a surrounding meningocele and a lipoma that extends from the conus to a subcutaneous fat collection. A 6-month-old female child presented with a large lumbosacral mass (14 cm × 12 cm × 10 cm) and weakness at the ankle joints since birth. Magnetic resonance imaging and computed tomography scan revealed a low-lying terminal lipomyelocystocele with holocord syrinx and partial sacral agenesis. The child was operated on successfully. This is an interesting and rare case of giant terminal lipomyelocystocoele with syrinx and a partial sacral agenesis. Terminal lipomyelocystocele should be included in the differential diagnosis of congenital lesions presenting as a lumbosacral mass and operated early.

Introduction

Terminal myelocystoceles (TMCs) constitute approximately 5% of skin-covered lumbosacral masses and are especially common in patients with cloacal exstrophy.[1] They are defined as occult spinal dysraphism with a localized, cystic dilatation of the central canal of the spinal cord herniated through a posterior spina bifida. TMC, truly an anomaly of the caudal cell mass, can be associated with anomalies of the anorectal system, lower genitourinary system, and vertebrae.[2] As is in our case, it may be associated with a lipoma which ends at the neural placode, when the term lipomyelocystocoele is applied.[1] Here we present a rare and interesting case of giant terminal lipomyelocystocoele with syrinx and associated partial sacral agenesis.

Case Report

A 6-month-old female child presented with a progressively increasing lumbosacral swelling which was present since birth [Figure 1]. The child was a full-term normal vaginal delivery and had normal developmental milestones. There was no history of CSF leak or meningitis. The patient had a weakness in ankle movement in both the lower limbs since birth. No obvious history of dribbling or urinary incontinence was forthcoming. On physical examination, there was a soft lumbosacral mass measuring 14 cm × 12 cm × 10 cm in size, obliterating the intergluteal cleft and with normal skin on its surface. The swelling was partially transilluminant and increased in size when the child cried. There were no nevi, hypertrichosis, skin defect, sinus or CSF leak. The head circumference was 44 cm and the anterior fontanelle was lax. The anterior abdominal wall and the genitalia were normal. The anus was patulous.

Figure 1

Lumbosacral mass obliterating the inter-gluteal cleft

Computed tomography and magnetic resonance imaging (MRI) revealed a giant terminal lipomyelocystocele [Figures 2 and 3] which contained a trumpet like flaring of the central canal of the distal spinal cord and a meningocele located around the dilated central canal, which bulged into the subcutaneous region along with subcutaneous fat tissue. Associated features of partial sacral agenesis in the form of absent dorsal and left sided elements were noticed. Syrinx was seen traversing the whole of the spinal cord. At surgery lipoma infiltrating, the myelocystocele was seen. Lipoma was excised. Caudal portion of trumpet shaped myelocystocele was resected and the remaining base was repaired using 6–0 monocryl suture. Dura was then closed with 4–0 silk suture.

Figure 2

Computed tomography scan showing spina bifida with the presence of trumpet like out-pouching of spinal contents

Figure 3

Magnetic resonance imaging T2 weighted sagittal section confirming the presence of terminal myelocystocoele

Post-operatively the child had wound infection, which required secondary suturing. The child recovered well with no post-operative deficits. Histopathology confirmed the findings of meningeal tissue with adipose and few wavy nerve fibers [Figure 4].

Figure 4

Microscopic picture showing meningeal lining, adipose tissue and few wavy nerve fibers

Discussion

Myelocystocoeles are defined as localized cystic dilatation of the central canal of the spinal cord. TMC constitutes 4–8% of lumbosacral occult spinal dysraphism. Epidemiologically, myelocystoceles arise sporadically; there is no known familial incidence. No true sex preponderance has been described.[3-5]

The TMC is composed of a low-lying conus medullaris with cystic dilatation of caudal central canal, a surrounding meningocele, and a lipoma that extends from the conus to a subcutaneous fat collection. The terminal cyst is lined with ependymal and dysplastic glia and does not communicate with the subarachnoid space.[6]

TMC can be deconstructed into essential and nonessential features. Essential features are present in all TMCs and constitute the core malformation, comprising an elongated spinal cord extending extraspinally into a cerebrospinal fluid-filled cyst that is broadly adherent to the subcutaneous fat. The functional conus resides in the proximal cyst or within the intraspinal cord and the caudal myelocystocele wall is nonfunctional fibroneural tissue. Non essential features include variable measures of hydromyelia, caudal meningocele, and fat, present in only some patients.[7]

The myelocystocele is due to a defect in secondary neurulation. The caudal neural tube forms via canalization and regression, beginning at day 48. If an insult disrupts retrogressive differentiation, regression fails to occur and an abnormally low conus results.[6] According to Pang et al., the core structure of TMC strikingly resembles a transitory stage of late secondary neurulation in chicks in which the cerebrospinal fluid-filled bleb-like distal neural tube bulges dorsally to fuse with the surface ectoderm before focal apoptosis detaches it from the surface and undertakes its final dissolution. Author theorizes that TMC results from a time-specific paralysis of apoptosis just before the dehiscence of the cystic distal cord from the future skin, thereby preserving the embryonic state.[7]

The majority of children present with a skin covered mass at the lower back, in the intergluteal cleft and may be of variable size. Midline abdominal and pelvic anomalies often accompany the TMCs. This constellation of abnormalities is best represented by the acronym “OEIS,” a complex which is described in the literature as including an omphalocele defect, exstrophy of the bladder, imperforate anus and spinal abnormalities, occurring together in the same patient.[8]

Many newborns with TMC have no neurological deficits but develop them with age. As the spinal cord is tethered in TMC, a slow neurological deterioration is expected with age, but some infants have precipitous loss of leg and bladder functions in early life coinciding with rapid enlargement of the myelocystocele.[7]

A myelocystocele can be diagnosed prenatally with high resolution fetal ultrasonography.[6]

MRI is the best noninvasive modality to diagnose all of the components of a TMC and the associated central nervous system findings.[910] MRI appearance is distinctive and is characterized by a "trumpet-like" flaring of the distal cord central canal into an ependyma-lined terminal cyst. Abnormalities of the vertebral column may occur and include lordosis, scoliosis and agenesis of the sacral parts.[2]

TMC should be repaired within the first few months of life or once the diagnosis is made regardless of whether there are preexisting deficits. The aim of the TMC repair is to create an internal milieu least conducive to resticking of the remaining neural tissue, with maximal elimination of any nonfunctional wall through the use of reliable intraoperative electrophysiology.[711]

Conclusion

Surgical correction of myelocystocele is not only for cosmetic reasons but also to untether the spinal cord prophylactically to prevent future neurological deterioration. During surgical corrections, it is important to perform a thorough intradural inspection to transect all adhesions, in order to prevent future deterioration due to the spinal cord re-tethering.