Cloacal exstrophy

High-resolution ultrasound is the screening method of choice for neonates with cutaneous signs of underlying spinal pathology. This examination does not require sedation, doesnot use radiation and is less expensive than computed tomography or magnetic resonance imaging. Ideally, sonograms should be obtained as soon as the cutaneous marker (sacral dimple, hairy patch, skin-covered mass) is found at the newborn examination.

Spinal sonography is the ideal screening test for neonates with cutaneous manifestations of underlying spinal pathology, including dorsal midline hemangiomas, skin-covered masses, hairy patches, sacral dimples and mongolian spots. Spinal sonography should also be performed on neonates who have other congenital anomalies associated with spinal cord malformations, such as vertebral body anomalies, imperforate anus, cloacal exstrophy, encephalocele and suspected VATER syndrome (vertebral defect, imperforate anus, tracheoesophageal fistula, and radial and renal dysplasia).

Spinal sonography does not require sedation of the infant, and it does not involve radiation. The examination can be performed in the nursery or in an incubator. The ultrasound study can be completed in approximately 20 minutes at a cost of about $195. Imaging Technique

The ultrasound images in this article were obtained using an Acuson 128 Computed Sonographic System with a 5-mHz linear array transducer. Sonolucent gel pads were used to offset the transducer, allowing the skin surface to be imaged. Aquasonic 100 transducer gel was used as the coupling agent.

Spinal sonography is performed with the child in the prone position. Images are obtained in both the longitudinal and transverse planes; these images are recorded on film for permanent record.

The position of the conus medullaris is determined in relation to the lumbar vertebral bodies. The entire length of the spinal cord is examined for evidence of displacement, enlargement or malformation. The thickness of the filum terminale is assessed, and the cauda equina is observed for abnormalities. The gel pad is then used to offset the transducer so that the skin surface and superficial soft tissues normally lost in the near field of the transducer can be imaged. Normal Spinal Cord

The spinal cord parenchyma is normally hypoechoic with a surrounding echogenic halo of nerve roots, blood vessels and arachnoid trabeculations (Figure la). Transverse images consistently demonstrate an echogenic dot in the center of the spinal cord. This dot represents the central end of the anterior median fissure, not the central canal, which is ordinarily closed at birth .5 In the longitudinal plane, the central end of the fissure is seen as a midline echogenic line (Figure 1b).

The lumbar enlargement and the conus medullaris are easily identified by the characteristic tapering of the distal end of the spinal cord (Figure I c). In the newbom, the conus is at the level of L3 (Figure 2). When the infant reaches three months of age, the conus should not be below the lower margin of L2.

The filum terminale initially passes in the midst of the roots of the cauda equina, but distally moves posterior to lie just beneath the dorsal dura. The filum then exits the dural sac and passes within the sacral canal to insert into the periosteum of the coccyx. Ultrasonically, only the intradural filum can be imaged; it is seen as an echogenic band, 2 to 3 mm in diameter, passing from the tip of the conus medullaris to the tapered end of the distal dural sac. The dural sac normally ends at the level of S2 (Figure 1 c) .

In both longitudinal and transverse planes, the normal interfaces between skin, subcutaneous fat, muscle and fascia should appear as continuous lines. Interruption of these planes suggests the presence of a dermal sinus.

Timing of the Examination

Excellent visualization of the spinal cord in neonates is possible because the midline posterior spinous processes do not completely ossify until several months after birth. This allows a temporary window for the transmitting and receiving of ultrasonic sound beams. After the infant reaches four weeks of age, the spinous processes become progressively echo-dense.

Ideally, sonography should be performed as soon as a cutaneous marker is recognized. This marker will most likely be detected at the newbom examination before the child leaves the hospital, or during the first wellbaby check-up at four to six weeks of age. However, an adequate study can be done on an infant up to six months of age. Cutaneous Signs of Spinal Abnormalities

Spinal sonography is ideal for evaluating a lumbosacral dimple, which is generally more significant if it occurs above the gluteal cleft. A dimple within the gluteal cleft is usually indicative of "spot welding" of skin and subcutaneous tissue to the tip of the coccyx. The coccygeal dimple is not associated with spinal pathology, but it may be a precursor to a pilonidal sinus or cyst in later life. All dimples should be evaluated to determine their position in relation to the vertebrae and to check for the presence of a dermal sinus tract.

The dermal sinus tract is seen as a hypoechoic band extending from the skin surface to the dural sac, disrupting the normal echo interfaces between fat, fascia and muscle. Ultrasound cannot determine if a dermal sinus penetrates the dura and extends intrathecally. Only computed tomographic (CT) scanning after myelography can follow this tract.

A dorsal skin-covered mass in or below the gluteal cleft is usually a sacrococcygeal teratoma. Ultrasound demonstrates the presence of cysts within the teratoma and defines the tissue planes around the mass. Ordinarily, the teratoma does not involve the spinal canal. A skin-covered mass above the gluteal cleft is most frequently a lipomyelomeningocele. Ultrasound demonstrates the position of the spinal cord and defines the extent of fat in and around the spinal cord, eliminating the need for further preoperative imaging studies.

Figures 3 through 7 illustrate the use of spinal sonography in children with various cutaneous signs of spinal abnormalities. Final Comment

Ultrasound is the ideal first imaging modality in neonates with suspected spinal pathology. Since ultrasound machines are portable, the examination can easily be performed in the nursery or the neonatal intensive care unit.

Unlike CT scanning or magnetic resonance imaging (MRI), spinal sonography does not require patient sedation, and motion artifactsarenotaproblem.Ultrasound examination does not involve radiation, and it is much less expensive than CT or MRI studies. CT or MRI evaluations should be considered only if the ultrasound study does not explain the patient's symptoms or adequately define the abnormality.

COPYRIGHT 1989 American Academy of Family Physicians
COPYRIGHT 2004 Gale Group