Anatomic and Functional Imaging of Immunoglobulin G4-related Disease and Its Mimics.

Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is an immune-mediated fibrosclerosing disease with tumefactive lesions infiltrated by IgG4-positive plasma cells. Initially described as autoimmune pancreatitis, IgG4-RD is now recognized as a discrete entity and is found to affect virtually any organ in the body. Common extrapancreatic sites include the biliary tree, salivary glands, periorbital tissue, lungs, kidneys, lymph nodes, aorta, retroperitoneum, and thyroid gland. Diagnosis-which relies on histopathologic, serologic, and radiologic features-can be challenging with the disease underdiagnosed, as IgG4-RD often mimics malignancy, infectious processes, or other immune-mediated conditions. Patients may present with signs of compression of nearby structures due to mass effect or with organ failure when the disease is left untreated. The clinical course is complex, with single- or multiorgan involvement and metachronous or synchronous occurrence of lesions. IgG4-RD responds well to glucocorticoid therapy, disease-modifying antirheumatic drugs, and B-cell-depleting biologic agents; prompt diagnosis is important to avoid delay in treatment and unnecessary pharmacologic or surgical intervention. While imaging features may not be specific for IgG4-RD, functional whole-body imaging with fluorine 18-fluorodeoxyglucose PET/CT is a useful adjunct for localizing extrapancreatic sites for biopsy, monitoring therapeutic response, and demonstrating disease relapse. The authors describe the pancreatic and extrapancreatic sites of involvement in IgG4-RD, with imaging features and patterns to aid in distinguishing IgG4-RD from its mimics through a multimodality approach with emphasis on functional imaging evaluation. ©RSNA, 2023 Quiz questions in the supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

Histiocytosis and Neoplasms of Macrophage-Dendritic Cell Lineages: Multimodality Imaging with Emphasis on PET/CT.

Histiocytosis is a rare inflammatory process characterized by pathologic infiltration and accumulation of cells derived from the monocytic lineage in normal tissue. It encompasses more than 100 different subtypes of disorders that were recently classified into five main groups: (a) Langerhans-related histiocytosis, (b) Rosai-Dorfman histiocytosis, (c) cutaneous and mucocutaneous histiocytosis, (d) malignant histiocytosis, and (e) hemophagocytic lymphohistiocytosis and macrophage activation syndrome. Langerhans cell histiocytosis is the most common histiocytic disorder. Less common types include Erdheim-Chester disease, Rosai-Dorfman disease, adult and juvenile xanthogranuloma, necrobiotic xanthogranuloma, histiocytic sarcoma, interdigitating dendritic cell sarcoma, Langerhans cell sarcoma, and hemophagocytic lymphohistiocytosis. Although the pathogenesis of these disorders may be attributable to mutations in the oncogenic driver, recent discoveries have shown that inflammation and fibrosis secondary to mutated histiocytes, rather than a proliferative cell mechanism, result in manifestation of the disease. Diagnosis, which relies on a multidisciplinary approach, is challenging and often delayed because clinical findings are nonspecific and may mimic malignant processes at radiologic evaluation. Compared with conventional imaging, PET/CT allows detection of the increased metabolic activity in histiocytes. Diagnostic algorithms for histiocytic disorders should include functional imaging with fluorine 18 (18F) fluorodeoxyglucose (FDG) PET/CT, which provides a comprehensive whole-body evaluation of their potential involvement with multiple organ systems and allows monitoring of therapeutic response. The most recent revised classification, pathophysiologic and clinical manifestations, sites of involvement, and imaging features of histiocytosis are described in this review and a multimodality approach is used, with emphasis on 18F-FDG PET/CT evaluation. ©RSNA, 2021.

Multi-Modality Imaging in Vasculitis.

Systemic vasculitides are a rare and complex group of diseases that can affect multiple organ systems. Clinically, presentation may be vague and non-specific and as such, diagnosis and subsequent management are challenging. These entities are typically classified by the size of vessel involved, including large-vessel vasculitis (giant cell arteritis, Takayasu's arteritis, and clinically isolated aortitis), medium-vessel vasculitis (including polyarteritis nodosa and Kawasaki disease), and small-vessel vasculitis (granulomatosis with polyangiitis and eosinophilic granulomatosis with polyangiitis). There are also other systemic vasculitides that do not fit in to these categories, such as Behcet's disease, Cogan syndrome, and IgG4-related disease. Advances in medical imaging modalities have revolutionized the approach to diagnosis of these diseases. Specifically, color Doppler ultrasound, computed tomography and angiography, magnetic resonance imaging, positron emission tomography, or invasive catheterization as indicated have become fundamental in the work up of any patient with suspected systemic or localized vasculitis. This review presents the key diagnostic imaging modalities and their clinical utility in the evaluation of systemic vasculitis.

Chest Wall Keloids Depicted by 18 F-Piflufolastat PET/CT Imaging.

ABSTRACT: Keloids are pathological scars from exuberant fibroproliferative collagen response and excessive extracellular matrix production usually extending beyond the original wound margins. Although keloids are mostly of dermatological concern, they could be incidentally depicted on scintigraphic planar and PET/CT imaging and could mimic other types of skin diseases. The authors present a case of chest wall keloids documented on 18 F-piflufolastat PET/CT during the evaluation of prostate cancer recurrence.

18F-FDG PET/CT of Malignant Presacral Masses in Currarino Syndrome.

ABSTRACT: The Currarino syndrome is characterized by 3 main features: anorectal malformation, presacral lesion, and dysgenesis of the sacrum and coccyx. The presacral lesion is usually benign with a rare occurrence of malignant degeneration. The author presents 2 cases of Currarino syndrome with presacral mucinous adenocarcinoma and neuroendocrine tumor depicted by 18F FDG PET/CT.

PET/CT of delayed uterine leiomyoma metastasizing to lung and femur.

Benign metastasizing leiomyomas are benign disseminated extra-uterine tumors in patients with prior history of uterine leiomyomas and may occur years after hysterectomy. The lung is mostly affected, with less common occurrence in the brain, heart, spine, retroperitoneum, and bone. The authors present the role of 18F-FDG PET/CT in the metabolic staging and post-surgical monitoring of a patient with lung and femoral involvement.

¹8F-FDG PET/CT imaging of the pancreas: spectrum of diseases.

Since the introduction of integrated positron emission tomography-computed tomography (PET/CT), it has a great impact on the field of oncology. Comparing to other conventional scanners, only PET/CT is capable of providing important information on accurate detecting, staging/restaging, and post-therapeutic monitoring of many cancers. Many studies have demonstrated that PET/CT changes the management in approximately 30% of all cancer patients. Because 2-((18)F)-fluoro-2-deoxy-D-glucose (FDG) is a nonspecific tracer, understanding the PET/CT limitations and pitfalls for various pancreatic conditions can lead to more accurate interpretation of PET/CT images, which ultimately would impact patient care. As a result, it is important for radiologists and other clinicians to familiarize themselves with a wide spectrum of pancreatic PET/CT findings simulating cancer from benign entities.

Usefulness of PET/CT imaging in systemic IgG4-related sclerosing disease. A report of three cases.

Autoimmune pancreatitis is the pancreatic manifestation of a novel clinicopathological disorder called systemic IgG4-related sclerosing disease. Beside the pancreas, this entity affects other sites (salivary glands, orbit, lung, thyroid, gallbladder, biliary tree system, kidney, abdominal aorta, retroperitoneum, prostate, and lymph node) by infiltration with IgG4-positive plasma cells. Several case reports and small case series have demonstrated the utility of integrated positron emission tomography/computed tomography (PET/CT) in monitoring therapy and documenting relapse and flare-up of autoimmune pancreatitis. However, there are no reports on the usefulness of PET/CT in selecting extrapancreatic sites for tissue sampling. We herein demonstrate the clinical utility of integrated PET/CT in 3 cases of systemic IgG4-related sclerosing disease for targeting extrapancreatic biopsy sites.

Parathyroid Scintigraphy with an Incidental Indirect Finding of Pancreatic Cancer.

Modifications of the biodistribution of 99mTc-sestamibi seen during myocardial perfusion and parathyroid imaging may be secondary to benign or malignant processes in visualized anatomic structures not related to the target organs of these imaging procedures. This article presents a case of pancreatic adenocarcinoma indirectly depicted on parathyroid scintigraphy.

11C-Choline PET/CT Depiction of Rectal Gastrointestinal Stromal Tumor.

ABSTRACT: 18F-FDG PET/CT is an established imaging modality for gastrointestinal stromal tumor evaluation and its posttherapeutic monitoring. 68Ga-PSMA has been recently reported with the incidental demonstration of this neoplasm on PET/CT. The author presents an uncommon case of this tumor detected by 11C-choline during the assessment of prostate cancer.

Cavernosal Metastasis From Prostate Cancer on 18F-Fluciclovine PET/CT.

Uncommon penile metastasis from prostate cancer has been reported on PET/CT imaging with F-FDG, F-fluorocholine, C-choline, and Ga-PSMA. The author presents an additional case of F-fluciclovine PET/CT depiction of proximal and distal cavernosal metastases from prostate cancer with corresponding contrast-enhanced CT findings.

Kinetics of Gallbladder Emptying During Cholecystokinin Cholescintigraphy as an Indicator of In Vivo Hormonal Sensitivity.

Cholecystokinin cholescintigraphy is used clinically to quantify gallbladder ejection fraction as an indicator of functional gallbladder disorder. It can also provide the opportunity to quantify an individual's responsiveness to the physiologic stimulant of gallbladder contraction, cholecystokinin, which is a major regulator of appetite and postprandial satiety. Methods: In the current work, we use cholecystokinin cholescintigraphy to quantify the kinetics of gallbladder emptying, including average and peak rates, in response to a standard cholecystokinin infusion. Results: We demonstrated that patients with no gallstones or biliary obstruction who empty their gallbladders completely in response to cholecystokinin, having an ejection fraction greater than 80%, exhibit a broad range of sensitivity to this hormone. Three distinct kinetic profiles were observed, with those most sensitive to cholecystokinin achieving the earliest peak and the fastest rate of gallbladder emptying, whereas those least sensitive to cholecystokinin have the latest peak and the slowest rate of emptying. Conclusion: Patients can have abnormal cholecystokinin stimulus-activity coupling as an effect of endogenous negative allosteric modulation by membrane cholesterol. This was predicted in ex vivo studies but has not, to our knowledge, previously been demonstrated in vivo. This type of kinetic analysis provides a tool to quantify cholecystokinin responsiveness in patients and identify patients who might benefit from a drug that would positively modulate cholecystokinin action to improve their appetite regulation and to better control their weight.

Prostate brachytherapy seed embolization to the right renal artery.

PURPOSE: We report three cases of seed embolization to the right renal artery after iodine-125 (I-125) transperineal interstitial permanent prostate brachytherapy. METHODS AND MATERIALS: Case 1: A 65-year-old man presented with right flank and back pain less than 4 months after prostatic seed implantation. CT evaluation for renal stone showed a seed embedded in the lower aspect of the right kidney. Case 2: A 73-year-old man complained of painless hematuria 3 years after prostatic seed brachytherapy. CT and subsequent abdominal angiography showed a seed embolization to a lower branch of the right renal artery. Case 3: An 84-year-old man presented with gross hematuria 7 months after prostatic seed implantation. Excretory urogram and subsequent CT demonstrated the right lower renal seed migration. RESULTS: Prostatic seed embolization to the right renal artery may cause pain and hematuria. This pattern of seed migration may be easily overlooked by imagers because it mimics renal lithiasis on cross-sectional imaging. Knowledge of prior history of permanent interstitial prostate brachytherapy and careful radiologic interpretation may help to achieve the correct diagnosis of rare renal seed migration. CONCLUSIONS: We present an additional atypical site of brachytherapy seed relocation in the right renal artery in 3 patients. This type of migration is probably secondary to pulmonary arteriovenous malformation or right-to-left cardiac shunts. Awareness of the propensity of seeds to dislodge and vigilance in imaging interpretation of prostatic brachytherapy recipients are necessary for the correct diagnosis of seed embolization.