Focal Hepatic Activity During Ventilation-Perfusion Scintigraphy Due to Systemic-Portal Shunt Due to Superior Vena Cava Obstruction From Histoplasmosis-Induced Fibrosing Mediastinitis

Superior Vena Cava Syndrome Induced Collateral Circulation on 99mTc-Macroaggregated Albumin Lung Perfusion Scintigraphy

Perfusion lung scintigraphy using SPECT/CT is one mainstay in diagnosing pulmonary embolism. Although typically almost all tracer will be accumulated in the lung capillaries, occasionally abnormal uptake can be detected. As superior vena cava syndrome leads to aberrant blood flow, tracer injected to an arm vein might partly circumvent the pulmonary capillary bed and accumulate in well-perfused anatomical structures. In this case, next to the commonly described liver enhancement, more prominent pseudo-uptake of various thoracic vertebrae was observable. However, a time-related FDG PET/CT demonstrated only the hepatic pseudo-uptake. Taken together, careful assessment of superior vena cava syndrome patient studies is highly recommended.

Multimodality Imaging of Focal and Diffuse Fibrosing Mediastinitis

Fibrosing mediastinitis is a rare benign but potentially life-threatening process that occurs because of proliferation of fibrotic tissue in the mediastinum. The focal subtype is more common and typically is associated with an abnormal immunologic response to Histoplasma capsulatum infection. Affected patients are typically young at presentation, but a wide age range has been reported, without a predilection for either sex. The diffuse form may be idiopathic or associated with autoimmunity, usually affects middle-aged and/or elderly patients, and is more common in men. For both subtypes, patients present with signs and symptoms related to obstruction or compression of vital mediastinal structures. The most common presenting signs and symptoms are cough, dyspnea, recurrent pneumonia, hemoptysis, and pleuritic chest pain. Patients with the diffuse subtype may have additional extrathoracic symptoms depending on the other organ systems involved. Because symptom severity is variable, treatment should be individualized with therapies tailored to alleviate compression of the affected mediastinal structures. Characteristic imaging features of fibrosing mediastinitis include infiltrative mediastinal soft tissue (with or without calcification) with compression or obstruction of mediastinal vascular structures and/or the aerodigestive tract. When identified in the appropriate clinical setting, these characteristic features allow the radiologist to suggest the diagnosis of fibrosing mediastinitis. Careful assessment is crucial at initial and follow-up imaging for exclusion of underlying malignancy, assessment of disease progression, identification of complications, and evaluation of treatment response. Online supplemental material is available for this article. ^©RSNA, 2019.