Peculiarities of pediatric renal trauma
A child's anatomy predisposes them to an increased risk of injury from blunt abdominal trauma. The kidneys are more mobile, and the protective perirenal adipose tissue is poorly developed. A critical clinical rule: any child with hematuria following trauma must undergo imaging, although the degree of hematuria itself does not reflect the scale of the emergency. It should be kept in mind that hypotension in children is a very late sign of blood loss.
- Computed tomography (CT): A mandatory first-line method for severe trauma, suspected pelvic fractures, or bladder rupture. CT requires the administration of iodinated contrast and involves a high radiation dose, which is why it is strictly avoided for routine dynamic monitoring.
- Ultrasound with Doppler flow mapping: The primary modality for mild trauma. An experienced specialist can rule out major ruptures. If the ultrasound findings are ambiguous or the clinical condition deteriorates, the patient is immediately referred for a CT scan. For follow-up monitoring (at 4–24 hours), ultrasound is used exclusively.
Pretransplant screening
The best outcomes are achieved when transplantation (especially from a living donor — live donation) is performed before dialysis is initiated. Modern desensitization techniques even allow for ABO-incompatible procedures.
Prior to the intervention, an ultrasound of the native kidneys and abdominal vasculature is mandatory. If the child has had previous venous catheters, vascular patency must be assessed using MR angiography. Critically important: due to renal failure, the administration of gadolinium is unacceptable; therefore, radiologists use non-contrast MR protocols (such as the time of flight technique).
Posttransplant monitoring
Initial ultrasound is often performed directly in the operating room or recovery room.
- Blood flow assessment: Color Doppler scanning is mandatory to check perfusion, especially if an en bloc graft from an infant donor was transplanted or complex anastomoses were formed.
- Detection of fluid collections: Ultrasound helps identify abnormal fluid collections. For instance, an avascular subcapsular hematoma may appear inconspicuous but can cause fatal graft compression.
- Radionuclide imaging: Routine use of 99mTc-DTPA is a thing of the past; it is now indicated only when urine leakage is suspected. However, 99mTc-DMSA scintigraphy at 4–6 weeks allows for establishing the baseline state of the renal parenchyma.
Diagnosis of complications
Unfortunately, no diagnostic imaging modality can reliably confirm graft dysfunction or rejection—the diagnosis is established solely on the basis of biopsy results. However, the biopsy itself can lead to the formation of arteriovenous fistulas, which appear on ultrasound as zones of high-velocity blood shunting.
A formidable complication of immunosuppression is post-transplant lymphoproliferative disorder (PTLD), associated with the Epstein-Barr virus (EBV). Ultrasound helps detect concomitant lymphadenopathy or organ infiltration, while cross-sectional imaging (CT or MRI) is utilized for precise staging.
Briefly: answers to topical questions
What pathological fluid collections can be detected by ultrasound in the early posttransplant period?
In the early posttransplant period, ultrasound examination can reveal the following pathological fluid collections:
- Urinoma (urinoma) — a collection formed shortly after surgery due to urine leakage resulting from ureteral anastomosis dehiscence.
- Hematoma (haematoma) — including avascular subcapsular hematoma, which is capable of causing significant compression of the kidney.
- Seroma (seroma) — one of the types of postoperative fluid collections in the lesser pelvis.
- Lymphocele (lymphocele) — a hypoechoic fluid collection that may be detected at later stages, for example, 5 weeks post-transplantation.
What vascular complications can occur in a renal transplant, besides arteriovenous fistulas?
In addition to arteriovenous fistulas, the following vascular complications can develop in a renal transplant:
- Renal artery thrombosis (renal artery thrombosis) — occurs in the early postoperative period, characterized by a complete absence of blood flow.
- Renal vein thrombosis (renal vein thrombosis) — manifests as an absence of venous flow and retrograde diastolic flow.
- Renal artery stenosis (renal artery stenosis) — a late complication associated with ischemic phenomena.
- Segmental infarction (segmental infarction) — a focal zone of decreased echogenicity with reduced vascularization.
- Pseudoaneurysm (pseudoaneurysm) — a false aneurysm, often occurring as a result of prior percutaneous interventions.
- Arteriovenous malformation (arteriovenous malformation) — an area of disorganized blood flow capable of causing hematuria.
CT is used to look for acute trauma; ultrasound is used for monitoring. Gadolinium in chronic renal failure is strictly prohibited.
Class and exam questions
Is CT used for routine monitoring of renal injury healing?
No, CT is not used for follow-up monitoring due to the high radiation dose. The method of choice in such cases is ultrasound with Doppler flow mapping.
What should be done if a child with mild abdominal trauma has significant pathology detected on ultrasound?
If severe vascular injury or a high probability of polytrauma is identified, the patient is immediately referred for contrast-enhanced CT, angiography, or surgical intervention.
How does the condition of the native bladder affect the transplant?
If the urinary bladder is non-compliant and has thickened walls, the risk of vesicoureteral reflux and the development of pyelonephritis in the transplanted kidney increases exponentially.
What else to study on this topic
- Indications and techniques for renal transplant biopsy
- Perinatal diagnosis of cystic renal diseases
- Diagnostic imaging of renal masses in children
- The use of voiding cystourethrography in pelvic trauma
- Peculiarities of contrast-enhanced ultrasound in pediatrics
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