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Congress: ECR25
Poster Number: C-20481
Type: Poster: EPOS Radiologist (educational)
DOI: 10.26044/ecr2025/C-20481
Authorblock: P. P. Lama, S. Morón Hodge, C. Oterino Serrano, L. Maté Miguel, L. T. Arnas, J. Rey Porras, J. Guisández Martín, S. Agueda Martín, C. Martín Hervás; Madrid/ES
Disclosures:
Pablo Pazos Lama: Nothing to disclose
Sara Morón Hodge: Nothing to disclose
César Oterino Serrano: Nothing to disclose
Laura Maté Miguel: Nothing to disclose
Laura Tello Arnas: Nothing to disclose
Jorge Rey Porras: Nothing to disclose
Jorge Guisández Martín: Nothing to disclose
Sonia Agueda Martín: Nothing to disclose
Carmen Martín Hervás: Nothing to disclose
Keywords: Abdomen, Kidney, CT, Ultrasound, Ultrasound-Colour Doppler, Education, Transplantation
Findings and procedure details

Before performing an ultrasound examination of a transplanted kidney, several factors related to the patient and the type of surgery must be investigated and considered:

  • Donor type: living or deceased
  • Time elapsed since surgery
  • Graft location
  • Type of anastomosis
  • Complications during surgery
  • Previous surgical history
  • Associated comorbidities
  • Clinical suspicion

After reviewing these clinical history details, the patient is evaluated using ultrasound as the primary technique. A baseline ultrasound with B-mode imaging and Doppler study is typically performed within the first 48 hours after surgery. The timing of subsequent follow-up studies will depend on graft evolution.

Assessment of Renal Parenchyma:

  • B-Mode: The following parameters should be analyzed (Figure 1).
  • Doppler study: It is necessary to implement it after the morphological study (Figure 2).

Renal Transplant Complications

They can be classified as vascular or non-vascular:

Vascular Complications:

  • Renal artery stenosis
  • Renal artery thrombosis:
    • Total
    • Segmental
  • Renal vein stenosis
  • Arteriovenous fistula (AVF)
  • Renal vein thrombosis
  • Pseudoaneurysm

Non-Vascular Complications:

  • Perirenal collections:
    • Hematoma/seroma
    • Urinoma
    • Lymphocele
    • Abscess
  • Urinary obstruction
  • Infections:
    • Bacterial
    • Viral: Polyomavirus
  • Parenchymal complications:
    • Acute tubular necrosis
    • Rejection
    • Drug-induced nephropathy
  • Others: Neoplasms

Some complications are more common in the early post-transplant period, while others occur later.

Renal Artery Stenosis (RAS)

Most common vascular complication (3% of transplants) and the most delayed (occurring between 3 months and 2 years post-transplant). It could manifest as refractory hypertension in 90% of cases.

In the perioperative period, isolated elevations in PSV may occur due to postoperative edema or technical issues during examination.

Key evaluation parameters:

  • Peak systolic velocity (PSV)
  • Waveform morphology
  • Intrarenal arterial resistive indices
  • Venous drainage pattern
  • Patient risk factors

Direct and indirect signs are shown on Figure 3, as well a case of our centre (Figure 4).

Renal Artery Thrombosis

Rare (0.45%) but severe complication that results in graft loss and requires urgent intervention. It is more common in the early postoperative period (within minutes to hours post-surgery).

Two types:

Total thrombosis (main renal artery affected):

  • Hyperacute rejection
  • Anastomotic occlusion
  • Arterial loops impairing flow
  • Intimal flap

Segmental thrombosis:

  • Acute rejection
  • Drug-induced vasculitis
  • Isolated segmental renal artery thrombosis

Ultrasound findings depend on the extent of arterial involvement (Figure 5). We provide two representative cases from our center (Figure 6 and Figure 7).

Renal Vein Stenosis

A rare complication that usually occurs in the early stages of the postoperative period.

It is secondary to vascular damage due to:

  • Extraction, transport, and implantation of the graft.
  • Excessive elongation and tension of the renal vein.
  • Post-surgical fibrosis.
  • Hemodynamic factors (arteriovenous fistulas).
  • Immunological factors (rejection, treatment with Cyclosporine A).

For renal vein stenosis to have an impact on renal parenchymal blood flow, it must be greater than 80% of the lumen. The functional status of parenchymal perfusion determines graft survival and, therefore, the possibility of rejection.

Imaging findings are shown on Figure 8, as well as an example on Figure 9.

Renal Vein Thrombosis

A rare complication (<5% in adult patients, 8% in pediatric patients) that leads to early graft failure in 8% of adults and 35% of pediatric patients.

It usually develops within the first five days post-transplant, with a peak incidence at 48 hours.

Diastolic flow reversal is highly suggestive of thrombosis but can also be seen in other complications, such as:

  • Graft torsion
  • Severe transplant rejection
  • Acute tubular necrosis
  • Drug-induced nephropathy

Imaging findings are shown on Figure 10, as well as a case on Figure 11.

Arteriovenous Fistula and Pseudoaneurysm

These are rare complications occurring after a graft biopsy. They typically present with hematuria and deteriorating renal function.

Small defects often resolve spontaneously, whereas larger ones require endovascular procedures if intrarenal or surgery if extrarenal.

The characteristics of both conditions are summarized in Figure 12. Representative cases are shown on Figure 13 and Figure 14.

Management:

  • If <2 cm: Conservative treatment.
  • If >2 cm or progressively enlarging: More invasive interventions (endovascular or surgical).

Perirenal Collections

They appear in 50% of renal transplants. Ultrasound findings are nonspecific, and the most critical factor in their evaluation is the timeline of their development.

The characteristics of these collections are summarized in Table 1. Cases are shown on Figure 15, Figure 16 and Figure 17.

Urinary Obstruction

This accounts for 2% of post-transplant complications, most commonly occurring within the first six months.

The most frequent cause is stenosis in the distal two-thirds of the ureter (90%), particularly following reimplantation into the bladder.

Causes of Ureteral Stenosis:

  • Surgical technique errors
  • Ureteral necrosis (ischemia/rejection)
  • Ureteral kinking

Other causes:

  • Pelvic fibrosis
  • Calculi
  • Papillary necrosis
  • Secondary compression by collections (most commonly lymphoceles)

Ureteral obstructions are often silent due to graft denervation. In some cases, they may cause elevated creatinine levels.

Possible consequences:

  • Periureteral fibrosis, leading to obstruction with mild dilation.
  • Mild dilation without obstruction, which can occur due to rejection or excessive bladder filling.

An example is shown on Figure 18.

Infections

80% of kidney transplant recipients experience at least one infection within the first year.

  • First 6 months: Opportunistic infections and cytomegalovirus (CMV) infections are common.
  • After 6 months: The pathogens are the same as in the general population.

Table 2 summarizes the microorganisms involved based on the timeline, while Figure 19 illustrates the imaging findings of the most common infections.

An example is given on Figure 20.

Parenchymal Complications

In the case of a marked decline in renal function, the following causes should be considered:

  • Acute tubular necrosis.
  • Rejection (hyperacute, acute, and chronic).
  • Drug-induced nephropathy (mainly cyclosporine).

In all these cases, the ultrasound findings are similar and indistinguishable from one another (Figure 21).

Acute Tubular Necrosis (ATN)

  • The most common cause of "delayed graft function."
  • More frequent in deceased donor transplants.
  • Usually resolves spontaneously within two weeks.
  • A biopsy is needed if renal function does not improve after one week.

Drug-Induced Nephropathy

  • Various medications can cause this condition, cyclosporine being a notable culprit.
  • Can occur acutely or after chronic use of the drug.
  • Ultrasound findings resemble rejection.
  • It is dose-dependent, so reducing the dose decreases toxicity.

Rejection

Rejection is classified into three types, differing in pathophysiology and timing of onset:

Hyperacute Rejection

  • Rare occurrence.
  • Develops immediately at anastomosis or within the first 3 days.
  • Caused by pre-existing cytotoxic antibodies.
  • Histopathology: Diffuse vascular thrombosis, mainly affecting arteries, arterioles, and glomeruli.

Acute Rejection

  • Common: Occurs in >50% of patients within the first year.
  • Symptoms: Fatigue, fever, weight gain, pain, or may be asymptomatic.
  • Two types:
    • Cell-mediated rejection
    • Antibody-mediated rejection

Chronic Rejection

  • Mediated by C4.
  • Most common cause of late graft loss.
  • Leads to cortical thinning and pelvicalyceal dilation.
  • Associated with recurrent acute rejections and non-immunological factors from the donor or recipient.

Other complications: Neoplasms

Renal transplant patients have an increased risk of developing malignancies.

Most common tumours:

  • Skin cancer
  • Lymphomas or PTLD (Post-Transplant Lymphoproliferative Disorder): Found in 8% of transplant recipients.
  • Urothelial tumors: Linked to cyclophosphamide use.
  • Renal adenocarcinoma: Slightly increased risk compared to the general population.

Renal Cell Carcinoma (RCC)

  • 90% of cases occur in native kidneys, usually associated with acquired cystic kidney disease (ACKD) secondary to dialysis.
  • 10% of cases occur in transplanted kidneys.

Routine screening is not cost-effective, except for patients with a history of RCC or ACKD, in whom screening is performed. However, in any follow-up imaging of a kidney transplant recipient, the native kidneys should also be evaluated, if they have not been removed.

A representative case is shown on Figure 22.

Structured Report

A detailed report is provided, outlining all parameters to assess in a kidney transplant recipient (Figure 23).
GALLERY