Pediatric Imaging

What Imaging Is Best for a Child’s Back Pain with a Lump or Skin Change?

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What Imaging Is Best for a Child's Back Pain with a Lump or Skin Change?

A 3-month-old infant presents for a routine check-up. During the examination, you note a small, deep dimple just superior to the gluteal cleft, associated with a small tuft of hair. The infant is neurologically intact, but the presence of this cutaneous stigma raises concern for an underlying spinal anomaly. You need to decide on the most appropriate initial imaging study to evaluate the spinal canal and its contents without exposing the infant to unnecessary radiation or sedation. This clinical workflow article addresses this specific scenario, for which the American College of Radiology (ACR) rates US spine area of interest as Usually Appropriate.

Who Fits This Clinical Scenario?

This guidance applies to pediatric patients, typically infants and young children, who present with back pain or, more commonly, an asymptomatic physical finding over the spine. The key inclusion criteria are the presence of a cutaneous marker suggestive of underlying spinal dysraphism. These markers include:

  • A palpable subcutaneous lump (e.g., lipoma)
  • A focal area of skin discoloration (e.g., hemangioma, hyper- or hypopigmentation)
  • A hairy patch (hypertrichosis)
  • A dermal sinus or draining tract
  • A deep or atypical sacral dimple

This workflow is distinct from other pediatric back pain scenarios. This guidance does not apply if the patient presents with:

  • Back pain with systemic red flags: If fever, night sweats, weight loss, or known malignancy are present, the workup shifts to evaluating for infection or neoplasm.
  • Back pain with neurologic deficits but no skin findings: While the differential may overlap, the absence of a cutaneous marker changes the pre-test probability and imaging pathway.
  • Back pain after significant trauma: This presentation requires a trauma-focused evaluation, where radiographs or CT may be indicated to assess for fracture.

What Diagnoses Are You Working Up in This Scenario?

The presence of a midline cutaneous lesion over the back is a significant finding because the skin and the central nervous system both develop from the embryonic ectoderm. An abnormality in one can signal an abnormality in the other. The primary concern is occult spinal dysraphism, a spectrum of congenital anomalies where the spinal cord and related structures are malformed but covered by intact skin.

Tethered Spinal Cord Syndrome: This is a primary concern. The spinal cord is abnormally attached to surrounding tissues, most often by a thickened filum terminale or a lipoma. This fixation restricts the normal upward movement of the conus medullaris as the child grows, leading to stretching and potential neurologic, urologic, or orthopedic dysfunction over time. Early detection is key to preventing irreversible damage.

Spinal Lipoma: These are fatty masses that are often associated with a tethered cord. They can be intradural, extending into the spinal canal and mingling with nerve roots, or extradural. A palpable lump on the back may be the external component of a larger lipomyelomeningocele.

Dermal Sinus Tract: This is a thin, epithelial-lined tube extending from the skin surface inward, potentially connecting to the dura or even the spinal cord itself. These tracts pose a significant risk for recurrent meningitis or the development of an epidermoid or dermoid inclusion cyst, which can cause mass effect.

Diastematomyelia (Split Cord Malformation): A less common finding where the spinal cord is longitudinally split into two hemicords, often by a bony or fibrous septum. This is frequently associated with other vertebral and spinal anomalies and can contribute to a tethered cord.

Why Is US spine area of interest the Recommended Initial Study?

For infants, spinal ultrasound is a powerful, non-invasive first step. The ACR designates US spine area of interest as Usually appropriate because it directly addresses the primary clinical questions in this scenario without the risks of radiation or sedation.

The key advantage of ultrasound in young infants (typically under 4-6 months) is the incomplete ossification of the posterior vertebral elements. This cartilaginous “acoustic window” allows sonographic visualization of the spinal canal, the position of the conus medullaris, the thickness of the filum terminale, nerve root motion, and the presence of any masses like lipomas or cysts. It is highly effective for determining the level of the conus medullaris, a critical step in screening for a tethered cord.

While MRI spine area of interest without IV contrast is also rated as Usually appropriate and is considered the gold standard for detailed anatomy, it has practical drawbacks as an initial test. MRI is more expensive, has limited availability, and almost always requires sedation or general anesthesia in infants to prevent motion artifact, which carries its own risks. Ultrasound serves as an excellent screening examination to determine if MRI is necessary.

Alternative modalities are rated lower for clear reasons:

  • Radiography spine area of interest is rated Usually not appropriate. Plain films are excellent for bone but provide no information about the spinal cord, nerve roots, or soft tissue masses that are the primary concern in this scenario. They may show associated vertebral segmentation anomalies but will miss the critical neural element findings.
  • CT spine area of interest without contrast is also Usually not appropriate. While superior to radiography for bone detail, it offers poor soft tissue contrast compared to MRI and involves significant ionizing radiation (Pediatric RRL: Varies), which should be avoided in children whenever possible.

What’s Next After US spine area of interest? Downstream Workflow

The results of the initial spinal ultrasound will guide the subsequent management and imaging pathway. The workflow typically branches into three possibilities.

If the ultrasound is definitively normal: A normal study in an infant under 4-6 months is highly reassuring. Key findings include a conus medullaris terminating at or above the L2-L3 disc space, a filum terminale less than 2 mm in thickness, and no evidence of masses or sinus tracts. In this case, for low-risk cutaneous stigmata (e.g., a simple sacral dimple), no further imaging is typically required, and clinical follow-up is sufficient.

If the ultrasound is definitively abnormal: If the ultrasound clearly identifies a low-lying conus, a thickened filum, a spinal lipoma, or a sinus tract, the next step is referral to a pediatric neurosurgeon. Pre-operative planning will almost always require a more detailed anatomical map. MRI spine area of interest without IV contrast (rated Usually appropriate) is the standard next study to precisely define the anatomy, delineate the relationship of a mass to the neural elements, and plan for surgical intervention.

If the ultrasound is indeterminate or limited: Sometimes, the study may be technically limited due to the child’s age (increasing ossification), body habitus, or patient motion. It may also reveal equivocal findings, such as a conus at the L2-L3 level where its position is borderline. In these cases, or for children with high-risk stigmata (e.g., a large hemangioma or palpable mass) despite a seemingly normal ultrasound, the next step is to proceed to MRI to resolve the uncertainty.

Pitfalls to Avoid (and When to Get Help)

Navigating this clinical scenario requires attention to a few common pitfalls to ensure timely and accurate diagnosis.

  • Delaying Imaging Past the Acoustic Window: The utility of spinal ultrasound diminishes significantly after about 4-6 months of age as the posterior elements of the vertebrae ossify. If suspicion is high, order the ultrasound promptly to avoid needing to proceed directly to a sedated MRI.
  • Misinterpreting Normal Variants: Not all findings are pathologic. A filar cyst or a prominent filum can be normal variants. Correlating with an experienced pediatric radiologist is crucial to avoid unnecessary downstream testing or anxiety.
  • Ignoring “Low-Risk” Stigmata: While simple sacral dimples located low within the gluteal cleft are often benign, any dimple that is deep, large, or located superior to the gluteal cleft warrants imaging.
  • Stopping with a Negative Ultrasound in High-Risk Cases: For very high-risk lesions, such as a large congenital hemangioma or a palpable lipoma, some specialists advocate for proceeding to MRI even if the initial ultrasound is reported as normal, as sonography can miss subtle abnormalities.

If the patient develops any new neurologic, urologic (e.g., abnormal voiding), or orthopedic (e.g., foot deformity) symptoms, escalate immediately with a referral to pediatric neurosurgery, regardless of prior imaging results.

Related ACR Topics and Tools

This article covers a single, specific scenario. For a comprehensive overview of all pediatric back pain presentations and their corresponding imaging recommendations, please consult the parent topic article. For additional resources on imaging selection, protocols, and radiation safety, the following GigHz tools are available.

Frequently Asked Questions

At what age does spinal ultrasound become ineffective for evaluating for a tethered cord?

Spinal ultrasound relies on the cartilaginous posterior elements of the infant spine as an ‘acoustic window.’ This window typically closes as the vertebrae ossify, usually between 4 to 6 months of age. After this period, ultrasound is generally not technically feasible or reliable for evaluating the spinal canal, and MRI becomes the necessary primary imaging modality.

If MRI is also ‘Usually Appropriate,’ why not just order it first?

While MRI provides superior anatomical detail, it has significant practical disadvantages for infants. It requires the patient to remain perfectly still, which necessitates sedation or general anesthesia, carrying inherent risks. Ultrasound is non-invasive, uses no radiation, requires no sedation, and is highly effective as a screening tool in the appropriate age group. It helps select only those infants who truly need the more intensive MRI for diagnosis or pre-surgical planning.

Does a simple sacral dimple always require imaging?

Not always. A ‘simple’ sacral dimple—defined as a single dimple less than 5 mm in diameter, located within the gluteal cleft, and less than 2.5 cm from the anus—is considered a low-risk finding. In an otherwise asymptomatic infant with a normal neurologic exam, these often do not require imaging. However, atypical dimples (large, deep, multiple, or located superior to the gluteal cleft) or any dimple associated with other skin stigmata should be imaged.

Is contrast ever needed for the MRI in this scenario?

For the initial evaluation of suspected spinal dysraphism, contrast is generally not necessary. The primary questions about anatomy, conus level, and the presence of a lipoma or thickened filum can be answered with non-contrast sequences. Therefore, ‘MRI spine area of interest without IV contrast’ is rated as ‘Usually appropriate.’ Contrast might be added if there is a concern for an associated tumor, vascular malformation, or post-operative changes, but it is not standard for the initial workup.

What if the child is older than 6 months and presents with a new skin finding?

If a child older than 6 months presents with a skin stigma and back pain or neurologic symptoms, the ultrasound window is closed. In this case, you would proceed directly to MRI as the initial imaging study. The ACR rates ‘MRI spine area of interest without IV contrast’ as ‘Usually appropriate’ for this scenario, and it becomes the de facto first-line test in older children.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026