Nephrogram - Procedure, Types and Indications

What Is Nephrogram?

Nephrogram is a diagnostic test conducted in nuclear medicine. A unique radioactive drug that has the quality to be utilized and secreted by the kidneys is administered intravenously. After this, a camera is kept behind the body at the renal region height. The camera acquires signals from the radioactive drug, and the results of the test derive from special processing conducted by a computer. The nephrogram equips data on both the anatomy and functionality of kidneys.

What Is a Computed Tomography Nephrogram?

The developments in the use of cross-sectional imaging, the computed tomographic (CT) nephrogram (contrast material enhancement within the renal parenchyma) has believed to play a greater part in the diagnosis of urinary tract disorders.

• Contrast-enhanced computed tomography is an important test in the diagnosis of renal disease, used increasingly in the acute care setting. Its advantages are accessibility, speed, high-spatial resolution, and rare contraindications compared to other modalities.

• The nephrogram directs to ways of renal enhancement as intravenous contrast courses through the renal parenchyma and collecting system, and when abnormal, can indicate precise diagnoses or disease etiologies.

• The nephrographic abnormalities are well demonstrated by CT, which includes both qualitative and quantitative ones.

• It also includes global or segmental absence or persistence of the nephrogram, striated pattern, rim pattern, and slowed temporal progression.

• Global absence is almost always unilateral and is greatly seen with blunt abdominal trauma with renal pedicle injury.

• Segmental absence can be due to focal renal infarction, considerably due to arterial emboli.

• Global persistence is more common than segmental persistence. It may be unilaterally caused by renal vein thrombosis, renal artery stenosis, or urinary tract obstruction, whereas it can be bilateral due to intratubular obstruction, systemic hypotension, and abnormalities in tubular function.

• Striated nephrograms can be unilateral or bilateral and are caused by acute pyelonephritis, ureteral obstruction, contusion, renal vein thrombosis, tubular obstruction, hypotension, and autosomal recessive polycystic kidney disease.

• The rim pattern is greatly associated with renal infarction and sometimes with acute tubular necrosis and renal vein thrombosis. A thorough evaluation of the CT nephrogram is a vital part of the abdominal CT examination.

When Is a Nephrogram Performed?

A urologist may need a nephrogram test under the following conditions:

• When other imaging tests, such as CT scans and ultrasound, showed indications of urinary obstruction.

• To investigate congenital abnormalities of the urinary tract.

How Is a Nephrogram Performed?

A nephrogram can be performed either as an outpatient or as a hospital inpatient. The health care provider explains the procedure and answers all the questions related to the test a patient may have. The procedure is as follows:

• A high amount of fluid needs to be drunk before the test.

• The technician or the health care provider places a venocatheter in the patient’s arm for the infusion of the radioactive drug.

• The patient is asked to lie on their on a radiology table with a special camera. The test is entirely painless.

• If there are any indications of urinary obstruction, the patient is given a diuretic. In this way, the healthcare provider will diagnose if the origin of the problem is anatomic or functional.

• As the test procedure is completed, the patient can get dressed and leave the laboratory.

• After the nephrogram, the patient can right away resume everyday activities without any restrictions.

• The patient may be asked to avoid contact with small children for some hours, as they will be emitting radiation.

How to Interpret the Results of a Nephrogram?

The healthcare provider will inform the patient if any abnormal findings are present. The patient is given additional instructions and information about therapeutic options that are appropriate for them. In case of doubts, the patient may be recommended to undergo more specific screening MRI (magnetic resonance imaging), ureteroscopy, etc.

What Is a Striated Nephrogram?

A striated nephrogram demonstrates the emergence of alternating linear bands of high and low attenuation. These attenuations extend through the corticomedullary layers of the kidney and are in a radial pattern on iodine-based intravenous contrast-enhanced imaging. It is important to note that a similar striated formation on gadolinium-enhanced pediatric magnetic resonance imaging may not be pathologic.

Pathology- Striations result from stasis and concentration of contrast material in necrosed or edematous tubules. It indicates increasing attenuation over time.

Etiology- The pattern is non-specific and can be seen in various conditions:

Unilateral striated nephrogram

• Acute ureteric obstruction.

• Acute renal vein thrombosis.

• Acute pyelonephritis.

• Acutely following renal contusion.

• Acute radiation therapy to the kidney.

Bilateral Striated Nephrograms:

• Autosomal recessive polycystic kidney disease (ARPCKD).

• Acute pyelonephritis.

• Acute tubular obstruction.

• Acute tubular necrosis.

• Hypotension.

• Idiopathic asymptomatic in some children.

What Is Delayed Nephrogram?

A delayed reprogram is generally described on plain film urography, but it is also visible on computed tomographic urography when there is an absence or reduction of the normal renal parenchymal enhancement on the nephrographic phase images. A delayed nephrogram is represented as unilateral and is usually differentiated from bilateral delayed nephrograms, also called persistent nephrograms.

Pathology- Normal enhancement of the renal parenchyma implicates contrast passing through the renal arterial bed to the glomeruli and nephrons before being finally concentrated into the collecting system. A temporal delay in this occurring may result in disruption of the pathways in this process.

Etiology- A number of renal conditions can lead to failure of the normal temporal progression of radiographic contrast, such as-

• Page kidney.

• Obstructive uropathy.

• Renal vein thrombosis.

• Extrinsic compression.

• Renal artery stenosis.

Radiographic features include abnormal kidney nephrographic enhancement in the delayed or urographic phase, which continues for a prolonged period of time. This is apparent in delayed images as the normal kidney exhibits contrast within the collecting system and ureters, while the abnormal kidney does not. These characteristics are different from non-enhancement of the renal parenchyma, which can occur in patients with renal infarction.

Conclusion:

The urographic nephrogram is a significant indicator of underlying functional and structural renal disease.Disorders of the kidney and urinary collecting system are generally experienced in acute care. Radiographic examination of the kidney after the intravenous injection of a water-soluble iodinated contrast material can exhibit the diffuse opacification of the renal parenchyma following such injection, a clue of renal blood flow and glomerular filtration. A constant nephrogram demonstrates obstruction of kidney drainage.