Which structure is likely to be identified in a sonogram of the left upper quadrant?

In a sonogram of the left upper quadrant, the identification of an accessory spleen is likely due to its anatomical positioning and echogenic characteristics. An accessory spleen, or splenunculus, typically appears as a small, homogeneous, hypo- or isoechoic structure situated adjacent to or near the main spleen in this region. This anatomical variant is relatively common and can easily be visualized with ultrasound.

The other structures listed, while they may occur in the abdomen, are less specifically associated with the left upper quadrant in a routine sonographic examination. Pseudocysts, for example, can be found throughout the abdomen but are more commonly associated with pancreatic disorders and may not be strictly localized to one quadrant. Adrenal adenomas are typically located on the adrenal glands, which are situated above the kidneys, often requiring specific imaging techniques to visualize adequately. Gastric neoplasms, while they can affect the stomach located in the upper abdomen, may not be directly identified in the left upper quadrant without additional context, especially since they can present similarly to other gastrointestinal structures.

The accessibility and potential visibility of an accessory spleen in the left upper quadrant make it the most probable choice in a sonographic evaluation of that area.