Diastematomyelia

Diastematomyelia (also known as a split cord malformation) refers to a type of spinal dysraphism (Spina bifida occulta) when there is a  longitudinal split in the spinal cord. Although traditionally it has been distinguished from diplomyelia (in which the cord is duplicated rather than split) the term split cord malformation (SCM) is advocated to encompass both conditions 6. For the purposes of this articles the terms diastematomyelia and split cord malformation are used interchangeably.

Epidemiology

Split cord malformations are a congenital abnormality and account for approximately 4% of all congenital spinal defects 6. 

Clinical presentation

The majority of patients with diastematomyelia are symptomatic, presenting with signs and symptoms of tethered cord, although patients wilh mild type II (see below) may be minimally affected or entirely asymptomatic 6. Presenting symptoms include:

leg weakness

low back pain

scoliosis

incontinence

Patients with diastematomyelia also frequently have other associated annomalies including: 

meningocele

neuroenteric cyst

dermoid

club foot

spinal cord lipoma

haemangioma overlying spine

Pathology

Classification

Split cord malformations are divided into two types according to presence of a dividing septum and single vs dual dural sac. 

type I: duplicated dural sac, with common midline spur (osseous or fibrous) and usually symptomatic

type II: single dural sac containing both hemicords; impairment less marked

Type I

Type I is the classic diastematomyelia, characterised by 1-6:

duplicated dural sac

hydromyelia common

midline spur often present (osseous or osteocartilaginous)

vertebral abnormalities: hemivertebrae, butterfly vertebrae, spina bifida, fusion of laminae of adjacent levels

skin pigmentation, haemangioma and hypertrichosis (hair patch) are common

patients are usually symptomatic presenting with scoliosis and tethered cord syndrome

Type II

Type II is milder than type I, and lack many of the features of latter:

single dural sac and no spur/septum

cord divided, sometimes incompletely so

hydromyelia may be present

spina bifida may be present, but other vertebral anomalies are far less common

patients a less symptomatic or may even be asymptomatic 

Radiographic features

Split cord malformations are more common in the lower cord but can sometimes occur at multiple levels.

50% occur between L1 and L3

25% occur between T7 and T12

An associated bony, cartilagenous or fibrous spur projecting through the dura mater forwards from the neural arch is visible in 33% of cases 1. 

Vertebral anomalies (spina bifida, butterfly or hemivertebrae) are common. Laminar fusion associated with a neural arch defect is a good predictor of diastematomyelia and occurs the level of the defect, or at an adjacent level. 

CT

CT is able to better image many of the features seen on plain films and in addition may demonstrate the bony septum. Modern scanners are also able to visualise the cord. 

MRI

MRI is the modality of choice for assessing children with split cord malformations. As well as being able to elegantly demonstrate the cord and presence of hydromyelia (if present), it can also assess for the presence of the numerous associated anomalies (see above).