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Background
IgG4-related disease (IgG4-RD) is a rare clinical entity that refers to a spectrum of diseases relating to lymphocytic infiltration of IgG-4 secreting plasma cells, resulting in fibrosis and scarring. IgG4-RD can affect any organ system and frequently presents in multiple organ systems. Within the head and neck, the primary tissues affected include the lacrimal gland, salivary gland, thyroid gland, paranasal sinuses, pituitary gland, and orbits. Less commonly reported anatomical presentations include involvement of cervical lymph nodes and the cavernous sinus. Given the variability of tissues affected, presentation and radiographic patterns are typically nonspecific. Thus, diagnosis of IgG4-RD requires astute recognition of radiologic signs and correlation with tissue pathology.

Educational Goals / Teaching Points
The goal of this exhibit is to present a pictorial review of known IgG4-RD as it pertains to presentations within the head and neck. The exhibit aims to highlight key radiographic features specific to anatomic locations across multiple imaging modalities. A secondary aim is to also correlate clinical presentation of disease with tissue-specific pathology, as IgG4-RD has varying presentations based on pattern of disease. Specifically, we highlight both common presentations, such as the orbits and the salivary glands, as well as more uncommon pathology, such as isolated lymphadenopathy or optic nerve sheath tumors. Following this exhibit, the viewer should be able to identify major tissues within the head and neck that can be affected by IgG4-RD, as well as consider key differential diagnoses by affected tissue type. The exhibit will also present insight regarding interdisciplinary work up to both diagnose and treat the condition.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The exhibit will focus on IgG4-RD in the head and neck, focusing on classic sites, such as the salivary gland and lacrimal gland, as well as less common sites of disease, including the optic nerve, cavernous sinus, and lymph nodes. Multimodal imaging features will be discussed, focusing on ultrasound, CT, and MRI. We will also compare these imaging findings to those seen in key differential diagnoses, such as Sjogren’s disease of the salivary glands or idiopathic orbital inflammation. Additionally, posttreatment imaging will be covered, including a demonstration of disease recurrence on surveillance image that was identified prior to the clinical manifestation of symptoms in a patient who had discontinued treatments.

Conclusion
IgG4-RD remains difficult to diagnose, as its presentation and may mimic many malignant processes. In particular tissues, such as the orbits, delayed diagnosis can lead to irreversible long-term consequences, such as blindness. Rapid and accurate diagnosis is important, as IgG4-RD commonly shows swift response to corticosteroid therapy. In younger patients, rituximab has also been suggested as a possible treatment. Thus, it is essential for providers to become familiar with both the anatomic areas that are typically affected by IgG4-RD as well as key radiographic features.