CT of the retroperitoneal space

Diagnosis of renal masses

Computed tomography is the imaging modality of choice for characterizing solid renal neoplasms. By evaluating X-ray attenuation values, the method reliably confirms the presence of fluid (typical of simple cysts) or adipose tissue (in angiomyolipomas).

CT provides precise visualization of the perinephric (perinephric) and entire retroperitoneal spaces. Multidetector CT (MDCT) enables high-quality multiplanar reconstructions, which is critical for preoperative planning, especially before laparoscopic or nephron-sparing surgeries. The method is also used to diagnose renal sepsis, detect tumor recurrence after radical nephrectomy, and assess the volume of hemorrhage.

Contrast phases

Adequate intravenous contrast enhancement is required for the most accurate analysis of masses. A standard examination consists of several phases:

• Unenhanced phase (unenhanced): required to search for calcifications (central calcification indicates malignancy in 87% of cases) and establish a baseline for assessing contrast enhancement.
• Corticomedullary phase: performed 25–40 seconds after contrast administration. It is useful for detecting anatomical variants of normal, evaluating tumor vascularity, and assessing the renal vein.
• Nephrographic phase: occurs at 90–100 seconds. The renal medulla is optimally enhanced at this time, allowing the detection of small medullary lesions and central masses.

Ideally, both contrast phases are used. If it is necessary to reduce the patient's radiation dose and use only one, the nephrographic phase should be chosen.

Malignancy staging

CT is the current standard for detecting metastases in retroperitoneal and mediastinal lymph nodes, particularly in testicular tumors. Lymphatic drainage from the testes follows the venous drainage and leads to retroperitoneal nodes at the level of the renal hila.

Metastatic pathways are predictable:

1. Left-sided lesions spread to the upper left para-aortic chain (closer to the left renal vein).
2. Right-sided lesions are located more caudally, in the anterior interaortocaval recess. Occasionally, they are located posterior to the third part of the duodenum, creating surgical challenges.

Cross-over (contralateral) or inferior spread to inguinal nodes occurs exclusively with marked ipsilateral involvement. It is worth noting that in stages 1 and 2 of the disease, CT may understage due to insufficiently opacified bowel loops or venous anomalies.

Alternative imaging modalities

If CT is not feasible, alternative approaches are used:

• Ultrasound (US): the modality of choice for children, pregnant women, and patients with renal impairment. It differentiates solid masses from cysts well, but is inferior to CT in cancer staging due to poor visualization of lymph nodes.
• Magnetic resonance imaging (MRI): used in cases of severe allergies to iodine-based contrast agents. The use of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) allows malignant tumors to be distinguished from benign ones with up to 83% accuracy.
• PET-CT: not used in initial staging, but highly useful for detecting residual disease (residual disease) after courses of chemotherapy.

Class and exam questions

What else to study on this topic

• Chest CT: search for peripheral and mediastinal pulmonary metastases
• Ultrasound differential diagnosis of cysts and solid neoplasms
• Diffusion-weighted imaging (DWI) in MRI
• Signs of pneumoperitoneum and retroperitoneal gas on plain radiography
• The role of duplex ultrasound in evaluating neoplastic processes

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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