IgG4 Related Disease Processes and Their Radiologic Findings

INTRODUCTION:
Immunoglobulin G4-related disease (IgG4-RD) is an autoimmune-mediated fibro-inflammatory condition capable of involving almost any organ, most common in men aged 60-70. It often presents with painless swelling and tumefactive lesions and is frequently misdiagnosed due to its resemblance to malignancy or infection. Diagnosis involves clinical, serologic, imaging, and histopathologic findings, with the ACR/EULAR, Japanese Comprehensive Diagnostic Criteria, and Mayo Clinic HISORt commonly used. While histopathology showing storiform fibrosis, obliterative phlebitis, and IgG4+ plasma cells remains the gold standard, imaging plays an important role in early recognition. This exhibit aims to serve as a consolidated resource to highlight common imaging patterns of IgG4-RD across organs and differentiate them from conditions with similar appearances.

MAIN BODY:
Head and Neck: Common manifestations involve the salivary and lacrimal glands, meninges, and thyroid. IgG4-related sialadenitis presents with painless bilateral swelling of the submandibular glands. Imaging shows symmetric, homogeneous enlargement of the salivary glands with loss of fatty hilum. These findings are similar to those seen in Sjogren's syndrome, however IgG4-related sialadenitis typically spares the parotid glands and lacks SICCA symptoms. Dacryoadenitis presents with upper eyelid edema and proptosis, with imaging demonstrating bilateral lacrimal gland enlargement extending into orbital tissues. Hypertrophic pachymeningitis refers to focal or diffuse dural thickening, often causing headaches and neurologic deficits. Contrast-enhanced MRI shows enhancing dural thickening. A rare but severe manifestation is Riedel's thyroiditis, presenting with a firm thyroid and compressive symptoms. CT shows hypoattenuation with invasive fibrosis into adjacent tissues, while ultrasound demonstrates a hypoechoic, fibrotic gland. Chest, Abdomen, and Pelvis: Type one autoimmune pancreatitis (AIP) is the most common abdominal manifestation and often the initial feature. It presents with abdominal pain, nausea, and vomiting. On imaging the pancreas appears diffusely enlarged and "sausage shaped" with loss of lobulations and delayed homogenous enhancement. A rim of peripheral hypoattenuation is common. Sclerosing cholangitis is often found with AIP, showing concentric wall thickening and smooth symmetric strictures in the intrapancreatic bile duct. IgG4-related sclerosing cholangitis can mimic cholangiocarcinoma, but produces long, smooth strictures rather than irregular, abrupt ones. IgG4-related retroperitoneal fibrosis encases the abdominal aorta and its branches, with imaging showing homogeneous soft-tissue density surrounding the infrarenal aorta and iliac arteries. Symptoms include back pain and hydronephrosis from medial ureteral displacement. It can be distinguished from malignancy as it usually spares the posterior periaortic space. Pulmonary involvement is also frequent, with CT showing nodules, ground-glass opacities, septal thickening, and bronchovascular bundle thickening. The multifocal, often bilateral nature of these findings, along with extrapulmonary disease, helps distinguish IgG4-related lung disease from infection or malignancy.

CONCLUSION:
IgG4-RD can mimic malignancy, infection, or other autoimmune conditions; however, manifestations often follow distinct patterns on imaging. Recognizing these patterns is crucial for correct diagnosis and timely biopsy. Imaging also plays a significant role in monitoring response to therapy and during tapering. This exhibit consolidates some of the most common manifestations of IgG4-RD and highlights recognizable patterns found on imaging to improve diagnostic confidence for these manifestations and other organ system involvements.