Utility of 3D-T2 space MRI sequence in diagnosing a rare cause of lower backache: horseshoe cord and meningocoele manqué in a case of composite split cord malformation

Technique (3D-T2-SPACE sequence)

3D-SPACE sequence is a rapid and efficient T2 sequence for evaluation of diastematomyelia extent, symmetric or asymmetric cords, horseshoe cord, extent of syrinx and associated thin MM bands. It is an advanced MRI technique which can produce high-resolution isotropic images which are less sensitive to flow, chemical shift and susceptibility artefacts. 3D-SPACE has an excellent ability to resolve T2 contrast which renders it the ability to distinguish superiorly cerebrospinal fluid from other structures. 3D isotropic data allows reconstruction of the images in multiple planes which are extremely useful for diagnosis and for surgical management.6 SPACE allows a superior topographical evaluation–visualisation of spinal cord tethering and adhesions. These findings have paramount surgical relevance when planning surgery for such a case, as if left undiagnosed and uncorrected, these can potentially cause persistent postoperative pain and discomfort to the patient.7 In our case 3D-SPACE, allowed us to visualise and characterise the thin MM bands and detect horseshoe cord which were not appreciated on the isolated T2 and T1WI sequences. The 3D-SPACE sequence was in fact done especially in a second sitting retrospectively to evaluate for the presence of these SCM associated lesions.

SCM description

SCM of the composite type is extremely rare, with only a few cases reported to date. In the literature, less than 1% of overall SCM cases were found to have composite type of SCM.8 9 The terms composite and compound are used interchangeably. The presence of multiple types of split chord characterises SCMs. At the same or separate levels, it can be type-1 or type-2, or a combination of both.10 Rarely, the division of the cord is unclear when the two hemicords are partially abridged, resulting in a horseshoe cord. Other forms of occult dysraphism, such as lipoma, dermoid, epidermoid, teratoma and sinus tract, are associated with composite lesions.11 12

SCM type-1 constitutes 40%–50% of SCM. It is usually associated with hyperplastic laminae and widening of interpedicular distance. The dural sac is always double, with two separate cords, and the spinal canal is divided into two symmetrical halves by an extradural bony or cartilaginous bar (as depicted in figures 1A and 2A), which can be tilted in the axial plane, resulting in an asymmetric partition of the canal. In such situations, the cord can be asymmetric with one of the cords appearing hypoplastic. Lumbar region is the most common location of spur followed by lower dorsal, cervical and upper dorsal regions, respectively. Double-level spurs are occasionally found. The two cords can extend over multiple segments and reunite caudally with the spur in the crouch on rare occasions.

SCM type-2 constitutes 50%–60% of SCM and is characterised by two symmetric or asymmetric hemicords in a single dural sac. There can be an antero-posterior fibrous band in between the two cords tethering the cords to the dura (as depicted in figures 1B and 2B).

Simultaneous development of neural and vertebral elements, leads to association of intraspinal anomalies like SCM with spinal deformities like congenital scoliosis and kyphosis.1 3 12 This was seen in our case.

MM description

According to James and Lassman’s original definition, MM is defined as the tethering of the spinal cord, nerve roots or filum terminale against the inner dorsal portion of the dura mater by fibrous bands, aberrant nerve roots and/or adhesions.13 It’s strongly associated with type-2 SCM. MM may be present in one-fifth of type-2 SCM. An overlying cigarette burn mark on the skin may be seen in 50% of instances.14 MM is a short tethering tract that terminates within the dura mater, epidural space or lamina, according to Rajpal.15 Long tethering tracts are tracts that end at the skin’s surface.

Peripheral nerves and ganglion cells, adipose tissue, blood vessels, epidermal cells, cartilage or bone, smooth muscle, central nervous system tissue and dermal/epidermal cyst elements can all be found in these tethering bands, in descending order of frequency, on histopathology.16 17 The most common constituent tissue is fibrous tissue. Usually the MM bands extend between dorsal surface of spinal cord to inner aspect of the dorsal dura. Sometimes, these may further extend through the dorsal dura mater upto underside of the lamina or within the surrounding fibrous tissue.14 15 While lumbar canal has been documented as the most common site of MM, it can rarely be seen in other regions also. These are seen as thin bands appearing isointense to the spinal cord on T1WI and hypointense to the spinal cord on T2WI. SCM, atretic meningocoeles and lipomas in lumbosacral region can be seen as associated findings.1 16 17

Clinical presentation and final management

The actual clinical presentation of the patients of SCM is highly variable, ranging from asymptomatic in half the patient population to symptomatic spectrum where they usually present with neurological and urological manifestations.

Factors contributing to the symptomatic presentation of the patient are associated with the presence of bony septum which prevents its normal developmental ascension with time, thus leading to tethering. Tethering of the cord is associated with back pain and can also lead to a compromise in the blood flow thus leading to tissue ischaemia.

Early surgical correction is usually recommended by the treating clinician. However, the type of split plays a major role in deciding the management. It is highly advisable for the patient to undergo surgery prophylactically in all asymptomatic cases of type-1 SCM while a conservative approach can be used in type-2 SCM. Preoperative condition of the patient has a significant impact on post-operative outcome. Intraoperatively monitoring continuously the neurophysiological status is also associated with better postoperative outcomes. Fluoroscopy can localise the level of the bony septum in type-1 SCM and site of the split in type-2 SCM. Laminotomy or laminectomy is undertaken a level above or below the septum in type-1 and at the level of the split and one level above or below as needed in type-1. The presence of syringomyelia does not have an impact on the clinical course of SCM and hence, it should not play a definitory role in surgically treating SCM.

Postoperatively, patients may show worsening of their neurological symptoms or may develop new onset deficits. These primarily include loss of sensations, neuropathic pain, urinary retention, bowel incontinence and paraparesis. However, mostly these complications are transient and the functions recover soon after surgery.16 18