The infant spine
NORMALANATOMY 1316Extraspinalandspinalanatomy 1316
Extraspinal 1316Spinal 1316
Intraspinalanatomy 1318Sacrumandcoccygealregion 1318Lumbarregion 1318Thoracicregionandconus 1319Cervicalregion 1320
CLINICALAPPLICATIONS 1322Spinaldysraphism 1322
Openspinaldysraphism(OSD) 1322Closedspinaldysraphism(CSD) 1322
Trauma 1330Vascularanomalies 1332Tumours 1332
Extraduraltumours 1333Intraduraltumours 1333Sacrococcygealtumours 1333Currarinostriad 1334
Development of real-time ultrasound and high-frequency linear array technology has taken imaging of the spine in early life well beyond early reports of using articulated arm static scanners. Clearer and more detailed information about spinal anatomy and pathology has made the modality increasingly useful.14 Its use in the older child and adult is severely limited by the presence of the surrounding posterior bony vertebral arches, whereas in the neonate these structures are incompletely ossified. At birth the pos-terior portions of the neural arches and spinous processes are still cartilaginous, providing an acoustic window into the spinal canal, which can be imaged in the sagittal (longitudinal) and axial (trans-verse) plane.By the end of the first year of life, fusion of the lamina into a
bony arch is complete in the lumbar region; ossification progresses cranially and is complete in the cervical region by 2 years of age. Visualisation of the spinal canal in the older child is only possible when a congenital or surgical bony defect is present, but ultrasound scanning rarely provides useful or diagnostic information in such
Tim Jaspan and Rob Dineen
cases and there should be no hesitation in proceeding to magnetic resonance imaging (MRI).Spinal ultrasound is most useful in the first few weeks of life,
when the posterior elements are unossified. The quality of informa-tion can be unrivalled if performed with care and attention to detail.5
Although MRI is now the modality of choice for spinal imaging, the neonatal spine presents a difficult challenge for MRI because of the small size of the baby, lack of suitable dedicated neonatal spinal surface coils and the high water content and immature myelination of the spinal cord, leading to relatively poor tissue contrast and signal-to-noise ratio compared to older infants and children. Pulsa-tile hyperdynamic cerebrospinal fluid (CSF) flow in the spine is particularly pronounced in infancy and early childhood, presenting additional interpretive problems, generating complex CSF flow pul-sation artefacts on spinal MRI.6 Conversely, ultrasound can reveal exquisite anatomical detail, guiding subsequent imaging triage.
The infants back should be inspected for cutaneous stigmata of occult spinal dysraphism. Although such findings may be the trigger for the study, clinicians sometimes miss subtle physical features (such as skin pits). Care should be made to look for a tiny ostium that may mark a dermal sinus track, which can be difficult to identify by ultrasound scanning.A high-quality real-time ultrasound machine is needed. A curved
linear or sector transducer is preferable for scanning the craniocer-vical junction. Linear array transducers are best for imaging the rest of the spine. In the neonate frequencies of 7.512 MHz are routinely used.The infant should be examined in the prone position, the spine
slightly flexed to flatten out the natural lower spinal lordotic cur-vature, lying prone over a pillow or bolster placed on the lap of the person holding the infant. Flexion maximises the acoustic window in axial scanning.Performing the examination following a feed may ensure the baby
is settled and more likely to lie still. Slightly warmed ultrasound gel will reduce the disturbance to the baby. Plenty of coupling gel on the skin should be maintained throughout the examination.The entire spine, from craniocervical junction to coccyx, is
scanned in the sagittal and axial planes, capturing representative images from each zone. A split-screen facility enables contiguous sagittal sections of the spine to be displayed together, providing a composite image of a longer length of spine.3 This is useful for determining anatomical landmarks, counting spinal vertebral levels and delineating the full extent of more complex pathological struc-tures. The extended field-of-view facility on some scanners achieves the same result.The examination starts at the sacrococcygeal level; identifying the
five sacral vertebral bodies provides a landmark for anatomical localisation. The presence and direction of spinal cord and nerve root movement should be looked for. A clip store helps in the
CHAPTER 67 The infant spine
demonstrated a spinal abnormality, ultrasound identified the index lesion. MRI confirmed normal appearances in all spinal ultrasound scans reported as normal, suggesting excellent sensitivity for ultrasound.However, caution must be exercised in evaluating studies that
include older children and where older generation MRI systems were used. Current state-of-the-art MRI, with superior surface coil technology, gradient systems, CSF and cardiac gating techniques, has improved the quality of MRI in the first few months of life.
Extraspinal and spinal anatomy
ExtraspinalThe skin surface appears as a narrow echogenic bilaminar stripe in the near field. Below this subcutaneous fat forms an intermediate to low echogenicity plane, immediately deep to which lies the lum-bosacral fascia. This commences in the coccygeal region (Fig. 67.1), forming a strongly echogenic unbroken stripe, which in turn blends with the hypoechoic interspinous ligaments and posterior paraspi-nal musculature in the lumbosacral region (Fig. 67.2). Gas within the rectum appears as an echogenic structure immediately deep to the coccyx (Fig. 67.1).
SpinalThe spinal column is composed of 33 individual segments, which are unfused in the cervical (7 segments), thoracic (12 segments) and lumbar (5 segments) regions. The 5 sacral and 4 coccygeal segments are partially fused. At term, echogenic ossification centres are present in all the vertebral bodies except the coccyx, and in paired centres that form the posterior neural arches. The latter do not fuse in the midline until the end of the first year of life.On sagittal plane imaging, the vertebral bodies form strongly
echogenic complexes lying deep to the anechoic CSF-filled thecal sac. The appearance of the posterior neural arches lying superficial to the thecal sac varies with the level of the spine and age of the patient, and they cast variable echogenic shadowing within the
appreciation of cord and root dynamics. With changes of position and with crying the spinal cord normally shows dorsoventral movement and the echogenic roots of the cauda equina move freely within the transonic CSF in the thecal sac. Pulsations of the anterior spinal artery and dancing motion of individual nerve roots may also be seen.1 The spinal cord does not normally pulsate with the cardiac cycle.2
In up to 10% of cases, a second (or more) dysraphic abnormality is present elsewhere in the neuraxis. Cord cavitation distant from the site of the lesion should be looked for, emphasising the need to examine the entire length of the cord.
Requests for spinal ultrasound often depend upon local experience and availability of appropriate sonographic expertise. Another factor is a lack of awareness amongst many referring clinicians as to the uses and limitations of ultrasound in early life.Ultrasound is recommended as the initial examination in sus-
pected spinal disease in the neonate. Where ultrasound is inconclu-sive or reveals pathology it should be followed by MRI. Over-reliance on ultrasound carries the risk of diagnostic errors and failure to detect potentially significant pathology. There should be a low threshold for proceeding to MRI.
The only absolute contraindication is an open neural tube defect because of the risk of contamination and infection. Increasing age is a relative contraindication; visualisation of the spinal canal is limited beyond early infancy. Over-reliance on ultrasound as the primary imaging modality outside of the first few weeks of life should be strongly resisted. Severe spinal deformity and bony ver-tebral anomalies can make ultrasound difficult. Scanning in the axial plane is most useful in these cases.
In a study of spinal disorders in infants undertaken in the 1990s, ultrasound was equally sensitive to MRI in the diagnostic yield.7 Thirty children with a mean age of 5.5 months underwent 38 spinal ultrasound scans; in 32 cases ultrasound matched the information seen on MRI. In 5 cases ultrasound showed the main abnormality but MRI gave additional information. In all 24 MRI studies that
Figure67.1 Sagittalimageofsacrumandcoccyx. The subcutaneous fat is hypoechoic, immediately below which lies the echogenic lumbosacral fascia (LSF). The echogenic sacral vertebral bodies (S) contrast with the hypoechoic coccyx (C). Note echogenic fat (F) in the sacral spinal canal and echogenic bowel gas (BG).
Indications for ultrasound scanning in early infancy
Highrisk Mediumrisk Lowrisk
Multiple congenital anomalies
Complicated sacral dimple (>5 mm diameter, >2.5 cm above anus)
Uncomplicated sacral pit or dimple (