Occult spinal dysraphism: detection during ultrasound for epidural blockade in children

Abstract

Occult spinal dysraphism is commonly asymptomatic and frequently associated with anorectal and genitourinary abnormalities. As neurological symptoms may develop due to distortion of the spinal cord and nerve roots as a baby grows, early detection is important to prevent neurological sequelae. There is a strong association between low spine anomalies and genitourinary and colorectal structures [1, 2]. Genitourinary, colorectal, and musculoskeletal systems are all of mesodermal origin and develop at the same time in the embryo, so that any insult inducing congenital vertebral malformations during organogenesis may also lead to congenital genitourinary or colorectal abnormalities [2]. If genitourinary anomalies are combined with VACTERL syndrome, there is a high incidence of tethered spinal cord [3]. In the series by Pierre-Kahn [4], 27% of patients with congenital spinal lipomas combined with visceral abnormalities, and 37.8% of these patients had genitourinary anomalies. Since the early 1980s ultrasound has been recognised as a screening test for occult spinal dysraphism in neonates and infants. Over the past 2 years, we have detected occult spinal dysraphism during ultrasound for epidural blockades in 4 of 500 children undergoing genitourinary surgery. The four children were aged 6–43 months and were undergoing hypospadias repair. Cases 1 and 2 had combined patent ductus arteriosus and atrial septal defect and case 3 had microtia and congenital thoracic scoliosis. A shallow hairy dimple or pit was seen in cases 1–3. Case 4 had no combined anomalies or cutaneous markers. On pre-puncture ultrasound using a high-frequency 8–13 MHz linear probe (LOGIQe™; GE Healthcare, Wauwatosa, WI, USA), low conus medullaris with thickened filum terminale were detected in four children. On MRI, a tethered spinal cord with lipoma of the filum terminale (cases 1, 3, and 4) and conus (case 2) were diagnosed (Fig. 1). Detethering of the spinal cord was performed 4–6 weeks postoperatively in cases 1–3. Low-lying conus medullaris (a) and thickened filum terminale (b) were showed on ultrasound. Low conus medullaris (c, left upper arrow) and lipoma of filum terminale (left, lower arrow; right) were showed on MRI. Our cases 1–3 showed shallow hairy dimples and pits. Studies have already shown that minor skin lesions, including shallow dimples, are possible normal variants in normal infants [5]. Nevertheless, occult spinal dysraphism should be considered if infants have cutaneous stigmata associated with congenital anomalies. While MRI is the most sensitive method for evaluating occult spinal dysraphism, spinal ultrasound is a simple and effective screening method for detecting abnormalities of the spine, including a low conus medullaris, a blunt conus medullaris, a thickened filum terminale, lipoma, fixed dorsal position of the cord in the thecal sac, and lack of pulsatile movement of the cord [6, 7]. Consequently, we recommend routine ultrasound prior to epidural blockade for postoperative analgesia in infants and children undergoing surgery with congenital anorectal and genitourinary anomalies.