Silent neurenteric cyst with split cord malformation at conus medullaris: Case report and literature review.

Split cord malformations (SCM) are a common pediatric abnormality where children present with features of tethering and backache along with varying neurological deficits. Multiple neural tube defects may co-exist in children having defects of primary and/or secondary neurulation. Co-existent neurenteric cysts along with type 1 SCM have been described very rarely in the literature. We report a case of silent neurenteric cyst at conus medullaris with SCM type 1 where the cyst was missed in the preoperative imaging. Until date, only 8 such cases of neurenteric cysts with SCM at lumbar region have been reported. We review the literature regarding co-existing dual pathologies of neurenteric cysts and type 1 SCMs in light of limited capacity of imaging modalities to detect small neurenteric cysts in presence of co-existent neural tube defects. Multiple spinal neural tube defects in children need more attention and precise microneurosurgical skills as management differs in each of them. Co-existence of such pathologies detected intra-operatively may need modifications in preoperative planning to achieve the best possible outcomes.

Introduction

Neurenteric cysts comprise 0.7–1.3% of all spinal axis tumors.[12] Kubic and Fulton first identified these lesions in 1928 and described them teratomatous cysts and later in 1934 Puusepp termed them as intestinomas.[34] The term neurenteric cyst was coined by Holocomb and Matson in 1954.[56] Lumbar spinal neurenteric cysts are rare when compared with other regions.[7] These cysts are most commonly found in upper ventral cervical and lower thoracic cord[8] where 90% of neurenteric cysts are located in the intradural-extramedullary region and the remaining 10% are extradural and intramedullary neurenteric cysts.[9] We report a similar case and review the existing literature regarding dual pathologies.

Case Report

A 12-year-old girl presented with complaints of low backache and difficulty in walking since childhood and pain radiating to both lower limbs. On examination, right plantar and dorsiflexion were mildly weak (Grade IV) and sensations of touch and pinprick were decreased by 20% in right L4 and L5 dermatomes. Magnetic resonance imaging (MRI) showed low lying cord with split cord malformation (SCM) type 1 from D12 to L3 with terminal syrinx. No other abnormality was evident [Figure 1]. Computed tomography scan showed bony septum at L1 region [Figure 2]. She was planned for D12 to L3 laminectomy and excision of bony cartilaginous spur at L1 level. Intraoperatively on opening the dura, a 2 cm × 2 cm small whitish globular lesion was identified. Whitish cheesy material came out of it once the wall was excised. Complete excision was performed, and dural tubes were repaired into one thecal sac subsequently. Postoperative recovery was uneventful. Histopathological examination revealed a cyst lined by cuboidal to ciliated columnar epithelium with focal stratification and occasional goblet cells with components of bone, cartilage, collagen, skeletal muscle tissue suggestive of type B neurenteric cysts.

Figure 1

Magnetic resonance imaging lumbar spine showing split cord malformation with low lying cord and terminal syrinx. Retrospective analysis shows a possible cystic lesion dorsal to the cord having a cerebrospinal fluid like intensity

Figure 2

Computed tomography showing the spina bifida defect along with bony septum

Discussion

The “dual” combination of neurenteric cysts with SCMs is an uncommonly reported neural tube defect. In our literature search, only eight cases have been documented so far [Table 1]. The incidence of neurenteric cysts is most commonly seen in first and second decades with a male preponderance (2:1).[10] Most commonly, patients present with localized spinal pain with or without fluctuating myelopathy/radiculopathy. This fluctuating nature of symptoms is mainly due to cyst volumetric flux associated with periodic cyst fluid leakage secondary to hemodynamic or osmotic changes.[611] Neurenteric cysts may be associated with other abnormalities of the spine like SCM, scoliosis, spina bifida, hemivertebrae.[1213] In few patients malformations of gastro-intestinal tract anal atresia, renal, cardiac and cutaneous changes can also be found.[14] MRI forms the best imaging modality for diagnosis of neurenteric cyst. Usually, these lesions are isointense on T1, hyperintense on T2 without enhancement on contrast. However, many variations have also been reported.[1516] Wilkins and Odum classified neurenteric cysts in 1976 into 3 types based on histopathological features.[17]

Table 1

Dual pathologies (split cord malformation along with neurenteric cysts) reported in the literature

Type A cysts

Mimic respiratory and gastrointestinal cuboidal or columnar goblet cells with ciliated or no ciliated components with a basement membrane support, which is composed of type IV collagen.

Type B cysts

Cysts with glandular organization usually producing mucin or serous fluid along with bone, cartilage, smooth muscle, striated muscle and lymphatic tissue.

Type C cysts

Consisting of all features of type A cysts along with glial or ependymal tissue.

The case reported here supports and strengthens the unified theory of embryogenesis which was postulated by Pang et al.[18] Authors illustrated development of all types of SCMs due to common embryo-genetic mechanism. Due to an onco-genetic error, usually there is a formation of adhesions between ectoderm and endoderm during 3rd week of embryonic life, which leads to formation of accessory neurenteric canal which becomes invested by mesenchymal tissue and forms endo-mesenchymal tract which splits the developing notochord and neural plates. The mesenchyme around the tract will result in osseocartilagenous or fibrous septum. Splitting of neural plates give rise to the formation of two hemicords and sometimes the endodermal lining of fistula may differentiate into neurenteric cysts by inducer molecules.[19]

Conus medullaris is an uncommon location for neurenteric cyst. Neurenteric cysts are not seen commonly at this location and hence, it can be easily missed. If detected during surgery (as in our case) the goal should be to remove the cyst completely as the recurrence rate ranging from 0% to 37% have been documented in the literature. Retrospective analysis of the MRI should be done in all such cases and we also could identify a cystic lesion carrying cerebrospinal fluid like intensity dorsal to cord at one place [Figure 1]. Our patient has been doing well in the follow-up and follow-up MRI will be done subsequently.

Therefore, dual pathologies may sometimes be encountered intra-operatively. We suggest that a contrast MRI may be helpful in delineating the cyst wall. However, gadolinium is not used in SCMs. Selective use in cases where cystic cavities are seen on imaging can be recommended. Its realization should make a surgeon more aware regarding recurrence rates of neurenteric cysts and hence complete excision of the cyst along with detethering should be the “modified” goal of surgery.