Tag Archives: Incidental findings

Mirror image artefact

This is one of the commonest artefacts encountered in NephroPOCUS. It is generated by the false assumption that an echo returns to the transducer after a single reflection. In this scenario, the primary beam encounters a highly reflective interface, the reflected echoes then encounter the “back side” of the structure and are reflected back toward the reflective interface before being reflected to the transducer for detection. The display shows a duplicated structure equidistant from but deep to the strongly reflective interface. Remember, time = distance in the ultrasound world, which means if the echoes take longer time to reach back to the probe, that structure is displayed farther from the top of the screen and vice versa. In other words, structures closer to the probe are displayed at the top of the image.

In this example, the diaphragm sitting next to the air-filled lung that is reflective acts as a mirror, and the mirror image artefact appears as hepatic parenchyma (or spleen on the left) in the expected location of lung. However, when there is pleural effusion, this artefact disappears (fluid is an excellent transmitter of ultrasound waves unlike air) and you’ll see an anechoic area above the diaphragm representing the effusion. In these cases, identification of thoracic spine sign confirms the diagnosis of pleural effusion.

You can watch my video 10 ~7:58 for more examples and better understanding of the mechanism of this artefact.

Hepatic Hemangioma

This image demonstrates hepatic hemangioma incidentally found while imaging the kidney. On ultrasound, hepatic hemangiomas appear as well-defined, hyperechoic, homogeneous lesions. Some of them may have posterior acoustic enhancement. The hyperechogenicity probably results from multiple fibrous interfaces between vascular spaces. If the lesion is in a fibrotic liver, that is background echogenicity, it may appear hypoechoic. Lesions >5 cm can have mixed echogenicity because of intratumoral thrombosis and fibrosis.

Ultrasound has a good accuracy in differentiating hepatic hemangioma from malignant hyperechoic masses (sensitivity of 94.1% and specificity of 80.0% for lesions less than 3 cm diameter). The absence of blood flow on Doppler exam is also a reliable sign to differentiate hemangioma from hepatocellular carcinoma, which frequently has intra- or peri-tumoral vascularity. Though the lesion is vascular, the blood flow is too slow to be picked up by Doppler usually. In hypoechoic lesions, a peripheral echogenic rim favors hemangioma, while a perilesional hypoechoic rim, known as the ‘target sign’, strongly suggests malignancy.

Asymptomatic patients with lesions <1.5 cm, but also including those with lesions ≤5 cm, can be reassured and observed without follow-up imaging. On the other hand, close radiologic follow-up of should be considered in patients with lesions >5 cm (e.g. CT scan yearly), particularly those in a subcapsular location. In the absence of symptoms, prophylactic resection is usually not recommended [UpToDate].

This image demonstrates a lesion of mixed echogenicity in a non homogeneous liver (cirrhosis) and ascites. It was diagnosed as HCC.

Accessory Spleen

Accessory spleen or a splenule is a congenital focus of healthy splenic tissue, that is separate from the main body of the spleen. The reported incidence is as high as 16% in patients undergoing contrast-enhanced abdominal CT. The most frequent location (22%) is posteromedial to the spleen; anterolateral to the upper pole of the left kidney; and lateral, posterior, and superior to the tail of the pancreas.

Why should we care about it?

For nephrology-related POCUS, it is important to be familiar with this entity because it may be confused with neoplastic growth of the kidney. Other important things to note about accessory spleen are: It can undergo hypertrophy after splenectomy, and can be responsible for the recurrence of hematological disorders for which the splenectomy has been performed if not removed during surgery. Occasionally, an accessory spleen may become symptomatic because of torsion, spontaneous rupture, hemorrhage or cyst formation and can cause an acute abdomen.

What does the image show?

The renal sonogram shown here demonstrates an approximately 1.5 cm hypoechoic well-circumscribed lesion outside the left kidney (not anchored to the kidney), which is an accessory spleen. It was confirmed by MRI.

The surgical image shown here is an example of hilar accessory spleen.