A New Approach to Ultrasound Study of the Left Adrenal Lodge

Abstract

Introduction:: Ultrasound examination of the left adrenal gland is generally associated with relatively low sensitivity and specificity and is strongly influenced by the operator’s experience, patient characteristics, and the type of equipment available. In particular, the left adrenal gland remains a structure that is difficult to investigate, even in expert hands. The possibility of improving the ultrasound exploitability of the left adrenal gland and therefore contributing to enhancing the overall diagnostic sensitivity of the technique, allowing for a more widespread application, could be represented by the addition, alongside traditional structural landmarks, of vascular landmarks. The improvement in the diagnostic sensitivity of ultrasound may allow for the use of this technique in selected categories of patients, particularly in the remote monitoring of already-known adrenal pathologies. background: Ultrasound examination of the left adrenal gland is generally associated with relatively low sensitivity and specificity and is strongly influenced by the operator’s experience, patient characteristic, and the type of equipment available. In particular, the left adrenal gland remains a structure that is difficult to investigate even in expert hands. The possibility of improving the ultrasound explorability of the left adrenal gland and therefore contributing to enhancing the overall diagnostic sensitivity of the technique, allowing for a more widespread application, could be represented by the addition, alongside traditional structural landmarks , of vascular landmarks. The improvement in the diagnostic sensitivity of ultrasound may allow for the use of this technique in selected categories of patients, particularly in the remote monitoring already known adrenal pathologie. Methodology:: In ultrasound, the normal adrenal gland is described as a solid formation of 6-8 +/-2 mm in thickness with the shape of an inverted V or Y letter or a λ shape consisting of a thin, linear, hyperechoic (medullary) central area surrounded by a hypoechoic (cortical) layer and possibly by a capsule that delimits it from the surrounding adipose tissue of the adrenal lodge. The ultrasound exploration of the adrenal gland is traditionally performed using a Convex 1-6 mHz probe, using structural landmarks such as the liver, spleen, upper renal pole, and diaphragm. On the right side, the liver provides a good acoustic window to the adrenal space, allowing visualization of the adrenal gland in approximately 90% of cases [1x, 2x]. On the left side, the spleen is used as an acoustic window, but its smaller size compared to the liver often cannot overcome the acoustic barrier represented by residual gas in the gastric and transverse colon/left colic flexure, even after intestinal preparation, reducing the possibility of visualizing the left adrenal gland up to 40-50% [1x, 2xy]. The exploration initially takes place with the patient supine to reduce meteoric overlap, then in the right lateral decubitus position; once the upper pole of the left kidney is identified with longitudinal and coronal sections along the mid and posterior axillary line, the left adrenal gland is located in the triangular space between the spleen, upper renal pole, and diaphragmatic crux by angling the probe anteriorly. As the kidney section decreases and disappears, the adrenal region becomes visible. Once the location is identified, the probe can be rotated on a traverse plane, considering that the left adrenal gland is medially located between the upper renal pole and the renal hilum, with the gland lying between the aorta medially and the kidney laterally. Considering that most adrenal expansions on the left tend to develop downward and inward, the left adrenal gland can also be explored, especially through an anterior approach, both in the long and short axes, using vascular landmarks, given the tight and consistent anatomical relationships of the gland with the large venous and arterial vessels in the region. The presence of gas-filled hollow organs can be partially reduced by conducting the exploration with moderate and constant pressure with the probe to displace them from the field of view. The vascular landmarks are represented by the: 1) abdominal aorta at the level of the emergence of the superior mesenteric artery, 2) the splenic vein, and 3) the vascular pedicle of the left kidney. The adrenal gland is located in the space between the aorta medially, the renal pedicle caudally, and the splenic vein anteriorly. Therefore, with a left paramedian axial section, the abdominal aorta is sought at the level of D12, where the superior mesenteric artery originates. Aligning with the splenic vein, which acts as the roof of the space under examination, the area of interest is explored by tilting the probe superiorly and medially towards the aorta, inferiorly and medially towards the left renal vein, and superiorly and laterally towards the renal border, trying to maintain the view of the splenic vein as the true anterior-lateral margin of the area. This position makes it possible to explore the tail of the pancreas and the Treitz. Discussion:: The ultrasound examination of the adrenal gland in adults is considered a method with low sensibility and highly operator -, patient-, and instrument-dependent compared to CT and MRI [3X] and currently has a limited and selective role in the management of patients with adrenal masses [4-6]. According to the International LLGG guidelines, the preferred methods for characterizing adrenal masses are CT, MRI, and PET/TC with 18F-fluorodeoxyglucose [4]. However, exploration of the adrenal glands has been considered an integral part of abdominal ultrasound studies since the 1990s [1X, 2X]. Under favorable conditions, the method is able to detect both neoplastic and non-neoplastic pathologies affecting the organ, contributing to the discovery of incidentalomas in this setting during an examination performed for reasons or symptoms not immediately related to the presence of an adrenal mass. [5]. The prevalence of adrenal incidentalomas detected during abdominal diagnostic investigations is reported to be around 5% of cases [7-10]. The sensitivity, in experienced hands, can be high even for masses smaller than 20 mm, especially on the right side [7]. The ultrasound examination may be indicated if the diagnostic workup of the adrenal mass does not reveal an immediate surgical indication and instead requires periodic monitoring. In cases where the conditions allow for accurate visualization and measurement of the lesion, for the absence of radiation exposure, simplicity of execution, and low cost, ultrasound examination may be preferred to CT for long-term surveillance [6-12], especially in young individuals. Conclusion: The addition of non-conventional acoustic windows and vascular landmarks characterized by anatomical constancy to the standard ultrasound examination can contribute to improving the sensitivity of the method, allowing for the identification of a greater number of incidentalomas and expanding the population that may benefit from ultrasound surveillance of known adrenal masses, especially of the left adrenal gland. A comparative study between the gold standard and the ultrasound method enhanced by vascular landmarks is desirable to quantify any potential improvement in sensitivity and specificity of the method in exploring the adrenal gland. This would serve as a premise for its practical application on a larger scale.