18F-Fluorocholine PET/CT is a valuable imaging tool in prostate cancer evaluation, especially for detecting biochemical recurrence. However, false-positive results, including benign adrenal adenomas, may occur. We present a case of a 62-year-old male with treated prostate cancer, who underwent 18F-FCH PET/CT due to biochemical recurrence. The scan showed focal uptake in the prostatic bed but also unexpectedly identified a 13 mm × 14 mm hypodense mass in the left adrenal gland. MRI suggested an adrenocortical adenoma, which was confirmed histologically. While adrenal radiotracer uptake is well-documented with other radiotracers, 18F-FCH role in characterizing adrenal lesions remains underexplored. This case raises the potential for 18F-FCH PET/CT to help distinguish benign from malignant adrenal tumors, warranting further investigation.
Adrenal Adenoma, 18 F-Fluorocholine PET/CT, Prostate cancer
Prostate cancer (PC) is one of the most prevalent malignancies in men, making early detection and surveillance crucial for effective management. Imaging techniques play an essential role in the diagnosis, staging, and monitoring of prostate cancer, particularly in detecting recurrence after treatment. Among these modalities, 18F-Fluorocholine ( 18 F-FCH) PET/CT has gained significant importance due to its ability to detect prostate cancer recurrence and metastasis. This imaging method capitalizes on the increased choline metabolism observed in prostate cancer cells, which is driven by the upregulation of choline transporters and enhanced choline kinase activity. This results in the accumulation of radiolabeled choline within the cancerous tissue [1]. 18 F-FCH PET/CT has proven to be effective in identifying local recurrences and distant metastases in patients with elevated prostate-specific antigen (PSA) levels, aiding in the decision-making process for further therapeutic interventions [2]. This modality has shown superior diagnostic accuracy compared to conventional imaging, particularly in cases where other imaging techniques such as CT or bone scans may fail to detect recurrence [3]. However, it is crucial to be aware of the potential for false-positive findings. These false positives can arise from various non-cancerous conditions, including benign adrenal adenomas, which can complicate the interpretation of 18 F-FCH PET/CT results. Adrenal incidentalomas, defined as asymptomatic adrenal masses discovered incidentally on imaging, are increasingly detected due to the widespread use of cross-sectional imaging. The prevalence of adrenal incidentalomas in the general population is estimated to be up to 10%, with adrenal adenomas accounting for 50-70% of these cases [4]. In patients with prostate cancer, the detection of an adrenal incidentaloma poses a diagnostic challenge, as it may represent a benign adenoma or, rarely, a metastatic lesion. The clinical significance of adrenal incidentalomas lies in the need to differentiate benign lesions from malignant tumors, as the management strategies for these two conditions differ significantly. Benign adrenal adenomas are generally non-functional and do not require surgical intervention, whereas malignant lesions, including adrenocortical carcinoma or metastatic lesions, may require surgical resection and/or systemic therapy [5].
This case report presents a unique finding in a 62-year-old male patient with prostate cancer who underwent 18 F-FCHPET/CT for biochemical recurrence and incidentally had an adrenal adenoma detected. The report explores the implications of these findings, the clinical significance, and the potential broader applications of 18 F-FCHPET/CT in the characterization of adrenal lesions.
A 62-year-old male with a medical history significant for PC presented to our department for biochemical recurrence of his disease evaluation following a rise in his prostate-specific antigen (PSA) level to 7.53 ng/ml. The patient had previously undergone a radical prostatectomy followed by adjuvant radiation therapy several years ago, and he had been in remission with stable PSA levels until this recent increase. His medical history was otherwise unremarkable, with no significant comorbidities, and he denied any new symptoms such as weight loss, hematuria, or bone pain, which would typically suggest metastatic spread. To assess for recurrence, an 18 F-FCH PET/CT scan was performed. The PET/CT acquisition parameters included a 60-minute uptake period following intravenous administration of 200 MBq of 18 F-FCH, with imaging performed from the skull base to the mid-thigh. The PET/CT scan revealed a focal area of increased 18 F-FCH uptake in the prostatic bed, with a maximum standardized uptake value SUVmax of 8.2, indicative of local recurrence. No signs of distant metastases were observed in common sites such as the lymph nodes or bones, suggesting that the recurrence might be localized and amenable to further treatment. Interestingly, the scan also revealed an unexpected finding: A focal area of uptake in the left adrenal gland. This uptake corresponded to a 13 mm × 14 mm mass on CT imaging, which appeared hypodense compared to the surrounding adrenal tissue. The SUVmax of 5.1 of the adrenallesion was measured at 5.1, a moderately elevated value, which raised the possibility of a malignant adrenal mass. However, given the patient's history of prostate cancer and the nonspecific nature of 18 F-FCH uptake in adrenal lesions, this finding required further investigation (Figure 1). Subsequent contrast-enhanced MRI with T1-weighted imaging revealed a characteristic washout pattern of the lesion, with a 50% washout in the delayed phase, suggestive of an adrenocortical adenoma. To definitively determine the nature of the adrenal mass, the patient underwent a percutaneous biopsy. Histological examination confirmed the diagnosis of a benign adrenal adenoma, consisting of well-differentiated adrenal cortical cells with no evidence of malignancy.
Adrenal incidentalomas are increasingly encountered in clinical practice due to the widespread use of advanced imaging techniques, such as PET/CT, CT, and MRI, for various diagnostic purposes. These incidental findings, often detected during imaging studies for unrelated conditions like prostate cancer recurrence, present a diagnostic challenge, particularly in patients with a history of malignancy. This case highlights the complexities associated with interpreting increased radiotracer uptake on 18 F-FCH PET/CT, where an adrenal adenoma was initially suspected to represent metastatic disease due to its metabolic activity.
An adrenal incidentaloma is defined as an asymptomatic adrenal mass discovered unintentionally during imaging performed for unrelated clinical indications. While the majority of these lesions are benign, with adrenal adenomas constituting 50-70% of cases, the possibility of malignancy cannot be overlooked, especially in patients with a known cancer history [4]. The clinical significance of adrenal incidentalomas lies in the need to differentiate benign lesions, which typically require no intervention, from malignant tumors, such as adrenocortical carcinoma or metastatic lesions, which may necessitate surgical resection or systemic therapy [6,7]. The increasing detection of adrenal incidentalomas, with autopsy studies reporting a prevalence of up to 10%, underscores the importance of accurate characterization to guide appropriate management [8]. In patients with prostate cancer, the adrenal glands are an uncommon site of metastasis, with bone and lymph nodes being the most frequent locations for metastatic spread. However, the detection of an adrenal mass in this population raises critical questions about its nature whether it represents a benign adenoma or a metastatic lesion. This diagnostic dilemma is particularly relevant in advanced stages of prostate cancer, where distant metastasis, though rare, remains a possibility [9].
Prostate cancer cells exhibit upregulated choline metabolism due to increased activity of choline kinase and overexpression of choline transporters, making 18 F-FCH PET/CT a valuable tool for detecting recurrent disease [10]. However, benign adrenal adenomas can also demonstrate increased radiotracer uptake, as seen in this case. The underlying mechanisms of 18 F-FCH uptake in adrenal adenomas are not fully understood but may be related to the metabolic activity of these lesions, including alterations in lipid metabolism and cell membrane turnover. This overlap in radiotracer uptake between benign and malignant lesions limits the specificity of 18 F-FCH PET/CT in characterizing adrenal masses, necessitating a multimodal diagnostic approach [11,12].
The clinical utility of 18 F-FCH PET/CT in differentiating benign from malignant adrenal lesions remains an area of active investigation. While this imaging modality provides valuable metabolic information, its inability to reliably distinguish between benign adenomas and malignant lesions highlights the need for complementary imaging techniques [13]. For example, CT and MRI can provide critical anatomical and functional details, such as lesion density, enhancement patterns, and washout characteristics, which are essential for accurate diagnosis [14]. In this case, the well-defined, hypodense appearance on CT and the 50% washout on MRI strongly supported the diagnosis of a benign adrenal adenoma, despite the increased radiotracer uptake on PET/CT.
The differential diagnosis of adrenal lesions includes a spectrum of benign and malignant entities, each with distinct imaging features. Benign adrenal adenomas, the most common incidentalomas, typically appear as well-circumscribed, homogeneous lesions with low attenuation on CT and rapid contrast washout on MRI. In contrast, malignant lesions, such as adrenocortical carcinoma or metastatic tumors, often exhibit irregular margins, heterogeneous enhancement, and slower washout patterns [15,16]. On 18 F-FCH PET/CT, benign adrenal adenomas may demonstrate variable radiotracer uptake, potentially overlapping with that of malignant lesions [17]. This underscores the importance of integrating functional and anatomical imaging to improve diagnostic accuracy. For instance, the combination of PET/CT with MRI can enhance the characterization of adrenal lesions by providing complementary information about their metabolic activity and morphological features. In cases where imaging findings remain inconclusive, biopsy may be necessary to establish a definitive diagnosis.
The management of adrenal incidentalomas in patients with a history of cancer requires a tailored approach, balancing the risk of metastasis against the likelihood of a benign lesion. Lesions that are small (< 4 cm), non-functional, and exhibit benign imaging features can typically be monitored with periodic imaging. However, functional lesions or those with suspicious characteristics may warrant surgical resection or further diagnostic evaluation [18]. In this case, the confirmation of a benign adrenal adenoma allowed for conservative management, avoiding unnecessary surgical intervention.
The increasing use of 18 F-FCH PET/CT in oncology highlights the need for further research into its role in characterizing adrenal lesions. While this modality is highly sensitive for detecting recurrent prostate cancer, its specificity for differentiating benign from malignant adrenal masses remains limited. Future studies should focus on identifying imaging biomarkers or combining PET/CT with advanced MRI techniques, such as diffusion-weighted imaging or chemical shift imaging, to improve diagnostic accuracy. Additionally, understanding the molecular mechanisms underlying FCH uptake in adrenal adenomas could provide insights into developing more specific radiotracers for adrenal imaging.
This case underscores the critical role of a multidimensional strategy in the assessment of adrenal incidentalomas, especially among oncology patients. Although 18F-FCH PET/CT serves as a sensitive modality for identifying recurrent prostate carcinoma, its utility in characterizing adrenal lesions is constrained, with a recognized potential for false-positive interpretations. Accurate diagnosis and management necessitate the integration of functional imaging with complementary anatomical modalities, such as contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI), alongside histopathological correlation. In individuals with prostate cancer, the identification of an adrenal mass warrants thorough clinical evaluation to differentiate metastatic disease from benign etiologies, thereby preventing unwarranted interventions. Multidisciplinary care teams and adherence to evidence-based guidelines are pivotal to ensuring optimal patient outcomes, mitigating procedural risks, and reducing the likelihood of misdiagnosis.
Figure 1: A 13 mm × 14 mm mass on CT imaging, which appeared hypodense compared to the surrounding adrenal tissue.