Neonatal and Infant Spine Ultrasound Review

Comprehensive practice flashcards for reviewing embryogenesis, vertebral anatomy, sonographic technique, and pathologies of the neonatal and infant spine.

What is the primary screening modality for detecting occult dysraphic conditions such as a tethered spinal cord in neonates?

High-resolution sonography of the spine, which has a diagnostic sensitivity equal to MRI for certain anomalies.

During which embryonic period do developmental defects of the spinal canal occur?

In the first $8.5\,\text{weeks}$ of life as the fetal nervous system develops.

What cutaneous back dimple features in an infant are considered most suspicious for underlying spinal dysraphism?

A dimple located more than $2.5\,\text{cm}$ above the anus, larger than $5\,\text{mm}$, or associated with asymmetry and other spinal lesions.

How many total vertebrae make up the vertebral column, and how are they categorized?

The vertebral column consists of $33$ vertebrae: $7$ cervical, $12$ thoracic, $5$ lumbar, $5$ sacral (fused to form the sacrum), and $4$ coccygeal fused bones.

What are the two structural components of an intervertebral disk shown in cross-section?

The peripheral part called the annulus fibrosus (composed of fibrocartilage) and the central part called the nucleus pulposus (an ovoid mass of gelatinous material containing water, collagen fibers, and cartilage cells).

What bony structures form the vertebral arch, and how many processes arise from it?

The vertebral arch consists of a pair of cylindrical pedicles (sides) and a pair of flattened laminae (posterior arch). It gives rise to $7$ processes: $1$ spinous, $2$ transverse, and $4$ articular processes.

Where does the spinal cord terminate inferiorly in adults versus in younger children?

In adults, the spinal cord terminates at the lower border of the first lumbar vertebra ($\text{L1}$). In younger children, it ends at the upper border of the third lumbar vertebra ($\text{L3}$).

What is the normal thickness measurement threshold for the filum terminale?

The filum terminale should measure $\le 2\,\text{mm}$ in thickness.

What is a filar cyst, and what is its clinical significance?

A filar cyst is a normal variant appearing as a small anechoic fluid collection in the filum terminale (remnant of a terminal ventricle or arachnoid pseudocyst) and has no clinical significance.

What is ventriculus terminalis in a neonate?

A normal variant characterized by a slight prominence or widening of the central canal at the caudal end of the spinal cord that typically disappears within the first few months of life.

Where does the dural sac end inferiorly in the neonatal spinal canal?

The dura mater ends on the filum terminale at the level of the lower border of the second sacral vertebra ($\text{S2}$).

What positioning techniques are used during sonographic evaluation of the neonatal spine?

The neonate is placed in a prone or lateral decubitus position with a pillow/rolled towel under the abdomen to flex the spine (separating posterior elements), along with slight elevation of the upper body to distend the caudal thecal sac.

What transducer frequencies are selected for small neonates versus chunky babies during spinal ultrasound?

Small neonates require higher frequencies ($15\,\text{MHz}$), while chunky babies require lower frequencies ($8\,\text{MHz}$).

What is the normal vertebral level for the tip of the tapered conus medullaris in a neonate?

In the upper lumbar canal, above the superior endplate of $\text{L3}$, with most spinal cords ending at the mid $\text{L2}$ level.

What four positive sonographic signs indicate a diagnosis of a tethered spinal cord?

1. Low-lying conus medullaris beyond the $\text{L2}$ level; 2. Caudal or posterior position of the spinal cord; 3. Absent or dampened pulsations of the cord and nerve roots; 4. Thickened filum terminale ($> 2\,\text{mm}$).

How does a dorsal dermal sinus differ from a pilonidal sinus?

A dorsal dermal sinus is an epithelium-lined tract extending from skin to the spinal canal/dura carrying a risk of meningitis. A pilonidal sinus occurs in the sacral/coccygeal region, does not connect to the spinal canal, and is not associated with a tethered cord.

What anatomical feature distinguishes a meningocele from a myelomeningocele?

A meningocele contains only fluid and meninges within the sac without spinal cord herniation, whereas a myelomeningocele contains neural elements (a flat non-tubulated neural placode and attached nerve roots extending into the sac).

What is hydromyelia, and where is it commonly seen in dysraphic conditions?

Hydromyelia is the dilation of the central canal of the spinal cord, often present focally just cephalad to the site of tethering in conditions like myelomeningocele or lipomyelomeningocele.

What spinal anomaly is demonstrated in this transverse ultrasound view?

Diastematomyelia, showing the sagittal division of the spinal cord into left and right hemicords, each containing an eccentric central canal.

What are the four categories of spinal lipomas?

1. Intradural lipomas; 2. Lipomyelocele; 3. Lipomyelomeningocele; 4. Fibrolipomas of the filum terminale.

How can the psoas muscle be used to identify the L1 vertebral level during spinal sonography?

The psoas muscle is visualized adjacent to the anterolateral spine at the level of the kidneys; following it superiorly to its origin corresponds to the $\text{L1}$ vertebral level.

What percentage of newborns have midline lower back dimples, and what is their clinical significance?

Midline dimples occur in approximately $2\%$ to $4.3\%$ of newborns, and most are low sacral or coccygeal pits without an associated tethered cord.

How does the first coccygeal vertebra (C1) appear on sagittal ultrasound compared to sacral vertebrae?

The first coccygeal vertebra ($\text{C1}$) is partially ossified and rounded in appearance, distinguishing it from the squarer sacral ($\text{S}$) vertebrae.

What three meningeal layers surround the spinal cord as illustrated in cross-section?

The dura mater (outermost fibrous layer), arachnoid mater (middle delicate layer), and pia mater (innermost vascular layer).