Faculty Bibliography

Renal oncocytic neoplasms present diagnostic challenges, both at imaging and pathologic evaluation. The World Health Organization classification of renal neoplasms defines a spectrum of oncocytic neoplasms, including emerging entities that help define previously uncharacterized or mischaracterized tumors. Low-grade oncocytic tumors and eosinophilic vacuolated tumors are distinguishable from other oncocytic neoplasms at pathologic evaluation and typically demonstrate indolent behavior. Nomenclature regarding hybrid neoplasms has been clarified in reference to hereditary cases associated with Birt-Hogg-Dubé syndrome. Preoperative diagnostic difficulties at imaging contribute to high rates of resected benign renal tumors, the majority being renal oncocytomas. The imaging appearances of oncocytic neoplasms are similar, and the inability to confidently diagnose them at imaging has led to increased resection rates. Preoperative renal mass biopsy may be preventative, but its utilization remains low, diagnoses can be equivocal, and establishing tumor aggressiveness may not always be reliable. Malignant renal oncocytic tumors, including chromophobe renal cell carcinoma, are generally considered the less aggressive subtypes of renal cell carcinoma. However, distinguishing them from the more aggressive clear cell subtype remains challenging, despite imaging frameworks designed to aid categorization. Active surveillance is a safe management option among biopsy-confirmed renal oncocytic neoplasms, but it remains uncertain which patients are suitable for this approach. Diagnostic imaging may assist in risk-stratifying oncocytic neoplasms, with mass enhancement, heterogeneity, and calcification potentially differentiating benign from malignant oncocytic neoplasms. Mass attenuation and heterogeneity may differentiate low-grade and high-grade cancers. Molecular imaging and other emerging techniques, such as MR fingerprinting, may play a role in the future. ^©RSNA, 2026 Supplemental material is available for this article.

Primary adrenal gland malignancies include adrenocortical carcinoma (ACC) and pheochromocytoma. For initial staging and restaging or surveillance of known or suspected ACC, MRI of the abdomen and pelvis without and with contrast, CT of the abdomen and pelvis with contrast, CT of the chest with contrast, and fluorine-18-2-fluoro-2-deoxy-D-glucose (FDG)-PET/CT, or FDG-PET/MRI are recommended to assess for local extent and distant metastases or to evaluate for recurrence. For initial staging and restaging or surveillance of known or suspected pheochromocytoma, MRI of the abdomen and pelvis without and with contrast, CT of the abdomen and pelvis with contrast, CT of the chest with contrast, DOTATATE PET/CT, or DOTATATE PET/MRI are recommended to assess local extent and distant metastases or to evaluate for recurrence. Meta-iodobenzylguanidine (MIBG) scan whole body with single-photon emission CT (SPECT) or SPECT/CT area of interest is an acceptable alternative for initial staging of known or suspected pheochromocytoma, in particular to determine eligibility for I-131 MIBG therapy. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Ultrasound is the imaging study of choice for the initial diagnosis of autosomal dominant polycystic kidney disease (ADPKD) due to its high diagnostic accuracy and ability to detect kidney cysts as small as 2 to 3 mm. MRI of the kidneys is also highly sensitive at detecting small cysts and is an alternative to US. MRI is the preferred modality for determining total kidney volume (TKV). TKV can be used as an imaging biomarker to predict kidney function decline, track disease progression, and evaluate the effectiveness of treatment. CT abdomen and pelvis with contrast is the test of choice for detecting suspected complications such as renal cyst hemorrhage, rupture, or infection. MRI of the abdomen without and with contrast can also be used for diagnosing complications of ADPKD and is usually appropriate regardless of kidney function. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Renovascular hypertension is the most common cause of secondary hypertension and occurs in 0.5% to 5% of individuals with hypertension. This is more common in individuals who have difficulty controlling their pressure or elderly patients with end-stage kidney disease. An evaluation for renovascular hypertension is indicated if there is a high level of clinical suspicion. The primary imaging modalities for assessing renovascular hypertension are ultrasound, CT, and MRI, and these options can vary depending on the patient's current renal status. Although ultrasound is beneficial since it uses nonionizing radiation, CT with contrast provides excellent spatial resolution. In patients with decreased renal function, MRI is a reliable alternative. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

BACKGROUND:Although most adrenal incidentalomas are benign, many are identified by single-phase contrast-enhanced computed tomography, which is unreliable for excluding malignancy. Virtual noncontrast computed tomography is a newer modality with the potential to better characterize adrenal nodules. METHODS:Virtual noncontrast computed tomography of adrenal nodules with available reference standard of true noncontrast computed tomography were identified (2016-2024). Images were evaluated for nodule characteristics including Hounsfield unit attenuation and variability. Nodules were classified as benign (≤10 Hounsfield units) or indeterminate/suspicious (>10 Hounsfield units) by true noncontrast computed tomography. Hounsfield units were compared between virtual noncontrast computed tomography and true noncontrast computed tomography. Variability in attenuation measurements was compared by evaluating Hounsfield unit differences 1 slice up and down from the chosen mid-depth image. Receiver operating characteristic analysis was used to define optimal virtual noncontrast computed tomography accuracy thresholds. RESULTS:After excluding 5 adrenal nodules due to suboptimal imaging, 67 nodules were identified. Based on true noncontrast computed tomography Hounsfield units, 23 nodules (34.3%) were benign, and 44 (65.7%) were indeterminate/suspicious. Hounsfield unit measurements for each nodule exhibited wide variability by both virtual noncontrast computed tomography and true noncontrast computed tomography. Virtual noncontrast computed tomography and true noncontrast computed tomography were significantly correlated with moderate effect size (Pearson coefficient 0.69, P < .001). Conflicting impressions occurred for 6 nodules (9.0%). Overall, virtual noncontrast computed tomography exhibited outstanding discrimination between benign and indeterminate/suspicious nodules (area under the curve 0.94). Maintaining a threshold of ≤10 Hounsfield units achieved 93% sensitivity, 76% specificity, and 84% negative predictive value, whereas ≤7 Hounsfield units achieved 100% negative predictive value. The functional utility of virtual noncontrast computed tomography as a rule-out test applied to 16% of nodules. CONCLUSION/CONCLUSIONS:Despite wide variability in Hounsfield unit measurements, adrenal nodules are well defined by both virtual noncontrast computed tomography and true noncontrast computed tomography. Well-reconstructed virtual noncontrast computed tomography images can accurately rule out malignancy in selected patients, potentially obviating the need for additional imaging.

Endometriosis is a common condition primarily impacting women of childbearing age. Despite increasing awareness that endometriosis can be diagnosed non-invasively with the correct imaging techniques, there exists a significant delay in diagnosis, to the tune of 5-10 years. This gap can be narrowed by understanding that this is a disease that lends itself to pattern recognition, and learning to recognize the characteristic patterns on any imaging study will allow earlier diagnosis and prevent long-term complications that can occur with progressive, untreated endometriosis. The disease is often multifocal and thus can present with a wide array of nonspecific symptoms. When clinical findings do not suggest endometriosis, patients often undergo non-targeted imaging, such as chest, abdominal, or pelvic computed tomography (CT); Magnetic Resonance imaging (MRI) studies optimized for neurologic or musculoskeletal indications; or ultrasound (US) exams performed for palpable masses or nonspecific abdominal pain. Familiarity with endometriosis's characteristic patterns across organ systems and how it can masquerade as other diseases helps radiologists broaden their differential to include endometriosis, even on studies not originally aimed at its detection. This review article will describe those imaging findings of endometriosis affecting various organ systems that mimic other pathologies and will enable the reader to pause and question whether endometriosis should be included in the differential.

The retroperitoneum, a complex abdominal compartment encompassing the anterior and posterior pararenal spaces, perirenal spaces, and great vessel space, is involved by both organ-based and non-organ-based pathologies. Imaging characteristics are invaluable in localizing pathologies to the either the retroperitoneum or one of its organs. A wide array of primary and metastatic neoplasms, including those of mesodermal, neurogenic, germ cell, sex cord-stromal, and lymphoid origin, may arise in this region. Frequently encountered non-neoplastic entities include fluid collections and retroperitoneal fibrosis. Integrating key clinical and imaging features is essential for the nuanced differentiation of this heterogeneous spectrum of pathologies.