When thoracic and abdominal imaging is done for unrelated clinical indications, adrenal tumors  are frequently seen. The detection of adrenal incidentalomas has significantly risen due to the  widespread use of multidetector CT and MRI [1]. An adrenal nodule may be inadvertently  discovered in 4–5% of people having CT scans. A subset represents clinically relevant entities  such pheochromocytoma, adrenocortical cancer, or metastatic illness, although the majority are  benign, especially adrenal adenomas.

Characterizing lesions that do not exhibit clear-cut benign imaging signs is the main problem in  radiological assessment. A lipid-rich adenoma is strongly supported by an attenuation value of ≤10  Hounsfield units (HU) in a homogenous lesion on unenhanced CT [2]. Nevertheless, over 30% of  adenomas have attenuation values more than 10 HU and are lipid-poor, which causes significant  overlap with pheochromocytomas and malignant lesions.

Another technique for characterisation is contrast-enhanced CT with delayed imaging. Adenomas  typically exhibit fast contrast washout after rapid enhancement [3]. The attenuation values acquired  prior to contrast, during the enhanced phase, and following delayed imaging can be used to  compute absolute percentage washout (APW) and relative percentage washout (RPW).  Traditionally, the diagnosis of adenoma has been supported by APW ≥60% and RPW ≥40% [4- 5].

An additional or complementary method is offered by MRI, especially chemical-shift imaging.  This method compares in-phase and opposed-phase images to identify tiny intracellular lipid. The  diagnosis of an adenoma is supported by a reduction in signal intensity on opposed-phase imaging.  With the added benefits of avoiding exposure to iodinated contrast and ionizing radiation, MRI is  especially helpful when CT results are still unclear [6].

However, neither modality is entirely conclusive in every situation. While certain adenomas may  not exhibit traditional washout, some pheochromocytomas and metastases may exhibit washout  features similar to those of adenomas. Therefore, rather than depending solely on one imaging

parameter, current evidence supports the personalized use of washout CT and chemical-shift MRI  [7-8].

Aim: To study the CT and MRI characteristics of indeterminate adrenal lesions and evaluate their  diagnostic value in differentiating benign from malignant adrenal masses.

Objectives

1. To assess the demographic and clinical profile of patients with indeterminate adrenal lesions.
2. To evaluate unenhanced CT attenuation values of adrenal lesions.
3. To calculate absolute and relative contrast washout percentages.
4. To evaluate chemical-shift MRI characteristics of adrenal lesions.
5. To compare CT and MRI findings with the final diagnosis.
6. To determine the diagnostic accuracy of combined CT and MRI characterization.

Study design and setting A prospective observational study was conducted in the Department of Radiodiagnosis of a tertiary-care hospital over an 18-month period. Study population The study included 100 consecutive patients with an adrenal lesion considered indeterminate on initial imaging or clinical evaluation. Inclusion criteria 1. Patients aged ≥18 years. 2. Presence of a focal adrenal lesion considered indeterminate on initial imaging. 3. Adrenal lesion measuring ≥1 cm. 4. Patients who underwent dedicated CT and/or MRI characterization. 5. Patients providing informed consent. Exclusion criteria 1. Previously characterized unequivocally benign adrenal lesions. 2. Patients with inadequate-quality CT/MRI examinations. 3. Patients unwilling to participate. 4. Patients with severe contraindications to contrast-enhanced CT or MRI where adequate characterization was impossible. 5. Diffuse adrenal enlargement without a definable focal lesion. 6. CT protocol CT examinations were performed using a multidetector CT scanner. Non-contrast images were obtained initially. Lesion size, morphology, homogeneity, calcification and unenhanced attenuation were recorded. MRI protocol MRI was performed using a 1.5-T or 3-T scanner. The protocol included: • Axial T1-weighted imaging • Axial T2-weighted imaging • In-phase and opposed-phase chemical-shift imaging • Fat-suppressed sequences • Diffusion-weighted imaging where available • Dynamic contrast-enhanced sequences where clinically indicated Signal intensity loss between in-phase and opposed-phase images was recorded as evidence of intracellular lipid. Homogeneous signal loss was interpreted as strongly supportive of lipid-rich adenoma. Statistical analysis Data were analyzed using statistical software. Continuous variables were expressed as mean ± standard deviation and categorical variables as frequencies and percentages. Independent-samples t-test was used for comparison of continuous variables between benign and malignant groups. Chi square or Fisher's exact test was used for categorical variables. A p-value <0.05 was considered statistically significant.

A total of 100 patients with indeterminate adrenal lesions were evaluated.

The mean age of the study population was 54.7 ± 12.6 years, with an age range of 22–79 years. There were 57 males and 43 females. The majority of lesions were detected incidentally during imaging performed for abdominal pain, gastrointestinal complaints, malignancy staging or evaluation of unrelated systemic disease.

Final characterization demonstrated 61 benign lesions and 39 malignant/potentially malignant lesions.

Table 1: Demographic and clinical characteristics of the study population

The malignant/potentially malignant group was significantly older and had significantly larger lesions than the benign group. A history of extra-adrenal malignancy was also significantly more frequent among patients with malignant lesions.

Table 2: CT characteristics of adrenal lesions

Benign lesions showed significantly lower unenhanced attenuation and significantly greater absolute and relative contrast washout. An APW ≥60% was present in 68.9% of benign lesions compared with only 12.8% of malignant/potentially malignant lesions.

Table 3: MRI characteristics of adrenal lesions

Signal loss on opposed-phase chemical-shift MRI was significantly more common in benign lesions. Malignant/potentially malignant lesions more frequently demonstrated heterogeneous T2 signal, restricted diffusion and necrotic or hemorrhagic components.

Table 4: Final diagnosis and diagnostic performance of CT and MRI

The most frequent diagnosis was adrenal adenoma (52%). Metastases constituted the most common malignant lesion. Combined CT and MRI demonstrated the highest diagnostic accuracy (94%), exceeding either CT or MRI alone.

Adrenal lesion characterization is still a crucial part of contemporary oncological and abdominal imaging. Identifying benign lesions with confidence while identifying malignant or hormonally active tumors that need additional treatment is the main goal [9]. Adenoma accounted for 52% of all lesions in the current investigation, making it the most common diagnosis. This result is in line with the well-established conclusion that most adrenal masses found by accident are benign. When typical imaging results are available, the incidence of adenoma further highlights the significance of avoiding needless invasive operations [10]. Compared to malignant or potentially malignant lesions, the mean unenhanced attenuation of benign lesions was substantially lower. This confirms that unenhanced CT attenuation is the first line imaging parameter. Lipid-rich adenoma is strongly suggested by a homogenous adrenal lesion with attenuation ≤10 HU. However, in a significant percentage of lesions, attenuation is not enough. Lipid-poor adenomas may overlap with metastases and pheochromocytomas and exhibit attenuation values greater than 10 HU [11]. This is the main reason more imaging is needed for ambiguous adrenal lesions. In the present investigation, benign lesions had substantially higher absolute and relative washout values. Just 13% of malignant or potentially malignant lesions had an APW ≥60%, compared to roughly 69% of benign lesions. These results corroborate the proven benefits of delayed contrast enhanced CT. According to conventional standards, APW ≥60% or RPW ≥40% are indicative of adenoma. However, washout is not perfect. Adenoma-like washout can be seen in pheochromocytomas, and some metastases, especially those from hypervascular original tumors, can similarly resemble adenomas [12]. Therefore, current guidelines place a strong emphasis on interpreting washout in relation to lesion shape, clinical history, and biochemical assessment. In our investigation, MRI offered further data. Only 12.8% of malignant or potentially malignant lesions showed signal loss on opposed-phase imaging, compared to nearly three-fourths of benign lesions. There was a statistically significant difference. Chemical-shift MRI is especially helpful for lipid-poor adenomas that are unclear on unenhanced CT because it can identify tiny intracellular lipid [13]. Additional morphological information was also shown by MRI. Malignant lesions were substantially more likely to have heterogeneous T2 signal, diffusion limitation, and necrosis/hemorrhage. When paired with increased lesion size, irregular morphology, and a history of cancer, these symptoms may raise suspicions but should not be interpreted separately. In our investigation, the combined CT-MRI technique yielded a 94% overall diagnosis accuracy. This lends credence to the idea that CT and MRI are complementing methods rather than antagonistic ones [14]. For lesions that are still unclear after non-contrast CT, current guidelines accept either chemical-shift MRI or washout CT as second-line imaging. Imaging can minimize needless biopsies, which is a significant clinical implication. Because of the possibility of major consequences, adrenal biopsy is not usually advised for incidental lesions, and suspected pheochromocytoma should be ruled out biochemically prior to biopsy [15]. Moreover, biopsies cannot always accurately differentiate between benign and malignant adrenocortical tumors. Therefore, a structured imaging strategy starting with unenhanced CT is supported by our findings. It is typically possible to classify lesions with clearly benign attenuation or distinctive macroscopic fat without the need for considerable further imaging. Depending on the clinical situation, renal function, radiation concerns, and availability, indeterminate lesions should either undergo chemical-shift MRI or dedicated washout CT [16].

CT and MRI are highly valuable complementary modalities for characterization of indeterminate  adrenal lesions. Unenhanced CT attenuation, contrast washout and chemical-shift MRI signal loss  are particularly useful parameters for identifying adenomas. Malignant lesions more frequently  demonstrate higher attenuation, lower washout, heterogeneous morphology, restricted diffusion  and necrosis or hemorrhage.

In this study, combined CT and MRI achieved greater diagnostic accuracy than either modality  alone. A structured approach incorporating imaging morphology, CT attenuation, washout  characteristics, chemical-shift MRI and clinical history can improve diagnostic confidence and  help avoid unnecessary invasive procedures.

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