Abnormalities of Pulmonary Venous Return

Abnormalities of pulmonary venous return in adults result from anomalous drainage of one or more pulmonary veins into a systemic vein, resulting in a left-to-right shunt. Partial anomalous pulmonary venous return (PAPVR) is most commonly encountered in adults in the upper lobes. PAPVR in the right upper lobe is commonly associated with a sinus venous atrial septal defect, whereas in the right lower lobe it is commonly encountered in association with other anomalies in Scimitar syndrome. Left upper lobe PAPVR is usually isolated. In some instances, patients can develop pulmonary over-circulation and hypertension, necessitating intervention. This chapter emphasizes CT and MR features key to recognizing and diagnosing these anomalies.

Glandular Enlargement

Glandular enlargement in the mediastinum is usually due to hyperplasia of thymus in the anterior mediastinum or thyroid enlargement with intramediastinal growth. Thymic enlargement is typically due to rebound hyperplasia associated with chemotherapy, radiation therapy, and stresses. Rebound thymic hyperplasia manifests as diffuse, symmetric enlargement of the thymus. MRI may be helpful in distinguishing thymic hyperplasia from neoplastic involvement of the thymus, as the former lose signal on opposed-phase T1-weighted MR imaging. Thyroid goiters may originate in the neck and migrate into the mediastinum or arise from an ectopic focus of mediastinal thyroid tissue. Goiters manifest as mediastinal masses that are similar in appearance to the thyroid gland, with intrinsic hyperdensity, hyperenhancement, foci of calcification and cystic change.

Cysts of the Mediastinum

Mediastinal cysts are fluid-filled lesions surrounded by a thin wall with an epithelial lining. These cysts are typically congenital, account for approximately 15-20% of all mediastinal masses, and may be found in any mediastinal compartment. Although mediastinal cysts may be initially detected on chest radiography, these lesions are optimally evaluated with computed tomography (CT) or magnetic resonance imaging (MRI). Cysts typically manifest as well-circumscribed, spherical lesions of water attenuation or signal, buy may appear heterogeneous when complicated by hemorrhage or infection. A focused differential diagnosis may be generated based on lesion location. For instance, bronchogenic cysts are most common in the middle mediastinum and pericardial cysts are typically found in the right cardiophrenic angle. Other mediastinal cysts include esophageal duplication and neurenteric cyst. Although meningocele is not a true cyst, it exhibits a cystic appearance on imaging.

Organizing Pneumonia

Organizing pneumonia (OP) is a nonfibrotic form of interstitial pneumonia that represents a manifestation of lung injury. It may be secondary to another process (such as vasculitis, collagen vascular disease, or drug therapy). When no inciting cause is found, the OP is believed to cryptogenic and the term Cryptogenic Organizing Pneumonia (COP) may be used clinically. Various patterns of OP may be encountered on imaging including classic (peripheral or bronchiolocentric consolidation), focal, crescentic, multinodular and fibrotic. The classic pattern is the most common, but the crescentic form (often known as the atoll or reverse halo sign) can be the most striking. The latter two patterns are more typical of OP associated with collagen vascular disease, most notably dermatomyositis and polymyositis.

Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) represents one of the most common chronic interstitial lung diseases. Usual interstitial pneumonia (UIP) is the pathologic diagnosis of IPF and can be diagnosed when honeycombing is present with a basilar and peripheral predominance and findings not typical of UIP are absent. In the current era, when a diagnosis of UIP is made with confidence on HRCT, biopsy can be avoided. Yet, one must be familiar with mimics of UIP/IPF (most notably pulmonary edema superimposed on emphysema) to avoid confusion misdiagnosis. Radiologists must also be familiar with potential complications of UIP including progression, infection, accelerated fibrosis (which can be lethal) and primary lung cancer (which has an increased incidence in UIP).

Sarcoidosis

Sarcoidosis is a systemic disease of unknown etiology, characterized by noncaseating epithelioid cell granulomas. Patients with sarcoidosis are frequently asymptomatic and may be diagnosed incidentally because of an abnormal imaging study. Sarcoidosis is a diagnosis of exclusion that warrants pathological confirmation in all cases. The distribution of granulomas in the lungs is characteristic and correlates with imaging findings; non-necrotizing granulomas classically exhibit a perilymphatic distribution. On chest radiography, the presence of bilateral hilar and right paratracheal lymphadenopathy, particularly in a young asymptomatic patient, should raise the possibility of sarcoidosis. On CT, a perilymphatic distribution (peribronchovascular, subpleural, septal) of abnormalities in the appropriate clinical context is highly specific for sarcoidosis.

Introduction to Iatrogenic Conditions

Post-therapy imaging interpretation can be challenging. In most practices, the main thoracic interventions include drug therapy, surgery and radiation therapy. In certain practices, especially in the absence of stereotactic radiation, radiofrequency ablation and cryoablation have gained a foothold. Post -therapeutic changes in the lung may be divided into two main categories: local and diffuse. Local changes are usually seen with radiation and percutaneous therapies. Diffuse changes mainly include organizing pneumonia and alveolar damage. The latter may be seen after both medical and surgical intervention. Two key questions must be answered when dealing with the treated patient: what was the prior therapy and when was the treatment. Both questions will help determine the significance of the imaging findings.

Silicosis and Coal Worker’s Pneumoconiosis

Silicosis and coal-workers pneumoconiosis (CWP) are fibrotic lung diseases secondary to the inhalation of free silica and coal dust. Exposure is typically occupational and occurs over many years before symptoms develop. Cough and shortness of breath are the most common presenting symptoms. Imaging features of silicosis and CWP are similar and often indistinguishable. Both silicosis and CWP result in upper lobe predominant disease. Pulmonary nodules are the most common imaging feature which may coalesce into progressive massive fibrosis. Lymphadenopathy and emphysema are additional findings seen in patients with silicosis and CWP. Silicosis has a higher incidence of tuberculosis and both pneumoconioses have a higher incidence of lung cancer.

Pulmonary Vasculitis

Vasculitis refers to inflammation of blood vessel walls that results in vascular wall destruction and ischemic injury to affected organs. Common vasculitides discussed herein include Takayasu arteritis (TAK), giant cell arteritis (GCA), antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides such as granulomatosis with polyangiitis (GPA) and eosinophilic granulomatosis with polyangiitis (EGPA), and anti-glomerular basement membrane (anti-GBM) disease or Goodpasture syndrome. Vasculitides are further subcategorized depending of the size of the predominantly affected vessels: large, medium and small vessel vasculitis. The affected vessel size strongly influences the clinical and imaging manifestations of the disease. Intrathoracic involvement is more common in small and large vessel vasculitides. Diffuse alveolar hemorrhage (DAH), a common manifestation of vasculitis, is considered a syndrome rather than a specific entity and will be discussed in this chapter. However, it should be noted that DAH may also result from non-vasculitic etiologies. The work up and diagnosis of patients with primary vasculitides is challenging and requires close collaboration between the clinician, the radiologist and the pathologist. Radiographic abnormalities are non specific or may be absent. CT and MRI are the imaging modalities of choice for the evaluation and follow up of these patients, and should be considered despite normal radiographics.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a progressive chronic systemic autoimmune disorder characterized by symmetric deforming erosive synovitis. Pulmonary involvement may occur in 18% of all patients with RA, is one of the most common extra-articular manifestations of the disease and is a major cause of morbidity and mortality. The most common pleuropulmonary manifestations of RA are rheumatoid-associated interstitial lung disease (RA-ILD), drug related lung disease, infection secondary to immunosuppression, necrobiotic nodules, organizing pneumonia, upper and lower airway disease, pulmonary vascular disease and serositis. A normal chest radiograph does not exclude RA-ILD. As disease progresses, radiographic abnormalities may become more apparent. Thin-section or high resolution computed tomography (HRCT) remains the study of choice to assess RA-ILD. Patients with RA-ILD have a slightly increased incidence of lung cancer, and radiologists must carefully scrutinize images looking for discrete nodules and masses.