Xanthogranulomatous Pyelonephritis Characterized on PET/CT

A New Era for PET/CT: Applications in Non-Tumorous Renal Pathologies

Non-tumorous kidney diseases include a variety of conditions affecting both the structure and function of the kidneys, thereby causing a range of health-related problems. Positron emission tomography/computed tomography (PET/CT) has emerged as a potential diagnostic tool, offering a multifaceted approach to evaluating non-tumorous kidney diseases. Its clinical significance extends beyond its conventional role in cancer imaging, enabling a comprehensive assessment of renal structure and function. This review explores the diverse applications of PET/CT imaging in the evaluation of non-cancerous kidney diseases. It examines PET/CT's role in assessing acute kidney injuries, including acute pyelonephritis and other forms of nephritis, as well as chronic conditions such as immune complex-mediated glomerulonephritis and chronic kidney disease. Additionally, the review delves into PET/CT's utility in evaluating complications in renal transplant recipients, identifying renal histiocytosis and detecting renal amyloidosis. The current review aims to promote further research and technological advancements to popularize PET/CT's clinical utility in diagnosing and treating non-tumorous kidney diseases.

Xanthogranulomatous Pyelonephritis: A Narrative Review with Current Perspectives on Diagnostic Imaging and Management, Including Interventional Radiology Techniques

Xanthogranulomatous Pyelonephritis (XGP) is a rare, chronic granulomatous inflammatory condition thought to arise secondary to a combination of obstruction, recurrent bacterial infection and an incomplete immune response resulting in focal or diffuse renal destruction. This destruction may be profound with the potential to infiltrate surrounding tissues and viscera. The imaging features of XGP can be ambiguous, mimicking malignancy, tuberculosis (TB) and malakoplakia earning the title of "the great imitator". Computed tomography (CT) is the mainstay of XGP diagnosis and staging, accurately quantifying the stone burden and staging the renal destruction, including the extent of extra-renal spread. Although some cases in children have been successfully treated with antibiotics alone, nephrectomy remains the most common treatment for XGP in adults. The specific management strategy needs to be tailored to individual patients given the potential constellation of renal and extrarenal abnormalities. Although XGP has classically required open nephrectomy, laparoscopic nephrectomy has an increasing role to play arising from the advancement in laparoscopic skills, technique and instruments. Nephron-sparing partial nephrectomy may be considered in the focal form. Interventional radiology techniques most often play a supportive role, eg, in the initial drainage of associated abscesses, but have rarely achieved renal salvage. This narrative review seeks to synthesise the existing literature and summarise the radiological approach and interventional radiology management situated in a clinical context.

Increased FDG Uptake on Juxtaglomerular Cell Tumor in the Left Kidney Mimicking Malignancy

Juxtaglomerular cell tumor is a rare and benign tumor arising from the juxtaglomerular apparatus that overproduces renin, resulting in secondary hypertension. A 29-year-old woman was incidentally found to have a left renal mass by ultrasonography in a routine health examination. Contrast-enhanced CT results suggested renal cell carcinoma. FDG PET/CT performed for metastatic workup showed increased FDG uptake to the left renal mass and did not reveal any other abnormal FDG-avid lesions. The renal mass was surgically resected and pathological examination confirmed the juxtaglomerular cell tumor of the left kidney.

Spectrum of Xanthogranulomatous Processes in the Abdomen and Pelvis: A Pictorial Review of Infectious, Inflammatory, and Proliferative Responses

OBJECTIVE

Xanthogranulomatous (XG) processes are rare inflammatory conditions with the characteristic pathologic feature of lipid-laden macrophages or histiocyte cells. Imaging findings are nonspecific and can simulate aggressive neoplastic processes. XG processes can be caused by infection, inflammation, histolytic process, or an inherited lysosomal disorder. XG infectious processes are mainly seen in cholecystitis and pyelonephritis, but several other organs can also be involved. Histiocytic processes can be divided into Langerhans and non-Langerhans cell histiocytosis. The non-Langerhans cell histiocytosis entities include Erdheim-Chester disease, Rosai-Dorfman disease, juvenile xanthogranuloma, and hemophagocytic lymphohistiocytosis. The inherited lysosomal disorders resulting in XG processes include Nieman-Pick, Gaucher, and other lysosomal storage disorders.

CONCLUSION

Radiologists need to be able to recognize features of xanthogranulomatous processes to help facilitate patient management.

Concurrent Diffuse Pyelonephritis and Prostatitis: Discordant Findings on Sequential FDG PET/CT and 67Ga SPECT/CT Imaging

A 45-year-old man underwent FDG PET/CT for initial imaging evaluation of recurrent Escherichia coli urinary tract infections, which demonstrated no significant FDG uptake in either kidney and subtle FDG uptake in the right prostate lobe. Subsequent Ga SPECT/CT demonstrated abnormal intense gallium uptake throughout the right kidney and entire prostate gland, clearly discordant with PET/CT findings and consistent with unexpected concurrent pyelonephritis and prostatitis. Although FDG has effectively replaced Ga in everyday clinical practice, the current case serves as a reminder that there is still a role for Ga in the evaluation of genitourinary infections.

Spectrum of malignant renal and urinary bladder tumors on 18F-FDG PET/CT: a pictorial essay

A wide variety of malignant renal and urinary bladder diseases can be detected on (18)F-FDG PET/CT. Although the PET/CT findings are often nonspecific, the aim of this atlas was to demonstrate that the spectrum of renal and urinary bladder malignancy that can be evaluated with PET/CT is much broader than current medical literature would suggest. PET/CT readers and oncologists should be aware of the variety of urological tumor types that can be detected on PET/CT and some of the patterns of (18)F-FDG uptake that can be observed in these cases.

Incidental Bilateral Renal Oncocytoma in a Patient with Metastatic Carcinoma of Unknown Primary: a Pitfall on (18)F-FDG PET/CT

Bilateral renal masses are uncommon but can raise a strong suspicion of primary or secondary malignancy, especially during the initial work-up of an oncology patient. Renal oncocytomas are benign renal tumors that are commonly discovered incidentally on diagnostic imaging with a small percentage occurring bilaterally. Although (18)F-FDG uptake in renal oncocytomas has been described, a case of a bilateral (18)F-FDG-avid renal oncocytoma has not been previously reported in the literature. A variety of malignant causes of bilateral (18)F-FDG positive renal masses are known, however it is important to include this benign etiology in the differential diagnosis. We report an unusual case of an incidental bilateral renal oncocytoma evaluated with contrast enhanced CT and (18)F-FDG PET/CT.

Increased (18)F-fluorodeoxyglucose uptake in benign, nonphysiologic lesions found on whole-body positron emission tomography/computed tomography (PET/CT): accumulated data from four years of experience with PET/CT

The use of (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG-PET) in the field of oncology is rapidly evolving; however, (18)F-FDG is not tumor specific. Aside from physiological uptake (18)F-FDG also may accumulate in benign processes. Knowledge of these (18)F-FDG-avid nonmalignant lesions is essential for accurate PET interpretation in oncologic patients to avoid a false-positive interpretation. Through the systematic review of the reports of PET/computed tomography (CT) studies performed in oncologic patients during a 6-month period, we found benign nonphysiological uptake of (18)F-FDG in more than 25% of studies. In half of these, (18)F-FDG uptake was moderate or marked in intensity, similar to that of malignant sites. A total of 73% of benign lesions were inflammatory in nature, with post-traumatic bone and soft-tissue abnormalities (including iatrogenic injury) and benign tumors accounting for the remainder. The differentiation of benign from malignant uptake of (18)F-FDG on PET alone may be particularly challenging as a result of the low anatomical resolution of PET and paucity of anatomical landmarks. Fusion imaging, namely PET/CT, has been shown to improve not only the sensitivity of PET interpretation but also its specificity. Aside from better anatomical localization of lesions on PET/CT, morphological characterization of lesions on CT often may improve the diagnostic accuracy of nonspecific (18)F-FDG uptake. Correlation with CT on fused PET/CT data may obviate the need for further evaluation or biopsy in more than one-third of scintigraphic equivocal lesions. Familiarity with (18)F-FDG-avid nonmalignant lesions also may extend the use of (18)F-FDG-PET imaging beyond the field of oncology. We have tabulated our experience with benign entities associated with increased (18)F-FDG uptake on whole-body PET/CT from 12,000 whole-body (18)F-FDG-PET/CT studies performed during a 4-year period.