The computed tomography (CT), and especially high-resolution CT (HRCT), when compared with plain films has higher sensitivity to detect mild differences in lung density, morphology, and distribution of the lesions, and associated abnormalities. Such characteristics make possible the HRCT to depict several diagnoses of pulmonary diseases.
Diffuse hyperdense pulmonary abnormalities could be divided into 4 patterns: (a) diffuse small hyperdense nodules; (b) multiple calcified large nodules or masses; (c) hyperdense linear or reticular pattern; and (d) hyperdense consolidations.1
Air-space consolidations seen in chest radiographs and CT are usually nonspecific, making the differential diagnosis difficult when based on such aspects. Clinical and laboratorial data could help narrowing diagnostic possibilities.
Measurement of the attenuation at noncontrast-enhanced CT inside the areas of consolidation can give the clue for the specific diagnosis. Attenuation higher than muscle seen as dense diffuse pulmonary opacities are due to calcium deposits in metastatic pulmonary calcification (MPC) and pulmonary alveolar microlithiasis (PAM), talc powder deposition in talcosis, and iodine accumulation in amiodarone lung toxicity. Deposition of iodinated oil embolism can occur also after transcatether oil embolization or after lymphangiography. Tuberculosis, amyloidosis, and silicoproteinosis may have focal calcifications, usually seen as small punctate calcified foci inside the areas of consolidation.
This pictorial essay has the aim to present various lesions that could present as consolidations with diffuse of focal high attenuation on CT, helping to make the diagnosis more confident and specific. The radiologic literature has limited information about such findings and the role of CT in the differential diagnosis.1
MPC is consequence of calcium deposition in normal pulmonary parenchyma.2 This condition can occur in a variety of disorders: primary and secondary hyperparathyroidism, chronic renal failure, intravenous calcium therapy, and massive osteolysis due to metastases or multiple myeloma.1 MPC usually presents as an asymptomatic condition. A fulminant course evolving to respiratory failure and early death is seen in some cases.2–4
HRCT findings are characterized by centrilobular fluffy ground-glass nodular opacities, which contain foci of calcification, seen mainly in the upper pulmonary zones. The calcifications can be punctate within the nodular opacities, ringlike, or diffuse (involving the entire nodule). These lesions may mimic air-space nodules, and rarely present as lung consolidations (Fig. 1). Most of these conditions can have high attenuation without consolidation. Other common feature seen in this condition is calcified vessels of the chest wall.1,2 Soft tissue window settings are useful to demonstrate extensive calcification.2
Histologic analysis in MPC is characterized by calcium deposition in alveolar septa, small pulmonary vessels, and bronchial walls.3,4 More severe interstitial calcification can result in dense consolidation. Calcium deposits may induce a lung reaction with alveolar organizing exudates evolving to fibrosis. These alveolar infiltrates may calcify.2
PAM is a rare chronic disease characterized by widespread calcific intra-alveolar concretions within alveolar spaces.4,5 The etiology and pathogenesis of microcalcific nodules formation are still unknown, probably related to an recessive autosomal heritage. Clinical symptoms are usually absent, and, when present, being characterized as dyspnea on exertion. Patients with PAM usually demonstrate extensive pulmonary abnormalities, with mild clinical manifestation. Therefore, radiographic diagnosis goes before any clinical complaints. Occasionally, progressive deterioration of pulmonary function may occur. Death is generally due to respiratory failure and “cor pulmonale.”4,5
Characteristic HRCT findings consist of multiple bilateral calcified micronodules measuring less than 1 mm in diameter, which tend to confluence.1,4 The lesions have predominance to cardiac borders and posterior pulmonary zones.4,5 Micronodules show often peripheral lobular distribution, resulting in a pattern resembling interlobular septa and subpleural calcification.3,5 Another feature seen on HRCT scans includes a very low attenuation line alongside the pleura, called “black pleural line,” and, probably due to subpleural cysts or a thin dark fat layer below the ribs.4 Apical “bullae” may also be seen in the lungs. Confluent nodules eventually present as air-space consolidations in patients with long-standing disease1 (Fig. 2).
Intra-alveolar accumulation of spherical microliths is seen at histopathology. In the early stages of the disease, the alveolar walls are normal; eventually interstitial fibrosis develops. Blebs and bullae are often present, particularly in the lung apices.1,4
Amiodarone-induced pulmonary toxicity is a serious adverse effect seen in patients receiving large doses of amiodarone to prevent cardiac arrhythmias. The treatment with this drug results in deposition of iodine in the lung parenchyma, a constituent of the amiodarone molecule. Clinical complaints are insidious, consisting of nonproductive cough, dyspnea, and occasionally fever. The diagnosis is one of exclusion because the signs and symptoms are not specific, and there is no laboratory test allowing the diagnosis.1,6
The most common CT findings include septal thickening, interstitial fibrosis, and consolidations. These opacities usually are peripheral in location. High iodine content makes possible the detection of amiodarone deposits in the lung by CT as a high-attenuation focal or multiple parenchymal opacities1,4,6 (Fig. 3). The association of dense lung air-space consolidations with high density of the liver and spleen is characteristic of amiodarone impregnation. However, it is not known whether this change in lung density indicates toxicity or the normal accumulation of amiodarone in lung tissue resulting from its therapeutic effects.6
Pathologic examination of the lung in amiodarone toxicity typically reveals chronic inflammation and fibrosis of the alveolar septa, and hyperplasia of type II pneumocytes. In addition, accumulation of intra-alveolar macrophages, which contain vacuolated cytoplasm with iodine inclusions, is also seen.4
Talc pneumoconiosis has been described in workers exposed to talc during extraction of magnesium silicate from mines, grinding, packing, and transportation of the product. Another form of talcosis is caused by the endovenous administration of talc seen in drug abusers. Clinical manifestations of talcosis consist of dry cough and chronic dyspnea. Late complications include pulmonary arterial hypertension and cor pulmonale.1,4
Earlier tomographic manifestations consist of a diffuse micronodular pattern with well-defined nodules, or diffuse ground-glass opacities. As the disease progresses the nodules can become confluent, resulting in hyperdense consolidations or confluent perihilar masses (Fig. 4). These lesions are similar to those seen in progressive massive fibrosis caused by silicosis. The dense opacities result from talc deposition within the pulmonary arterioles, capillaries, and interstitium. Panlobular emphysema involving predominately the lower lobes was seen almost exclusively in patients with talcosis secondary to endovenous injection of Ritalin.1,4,7
Pathologically, in the early stages of the disease, talcosis consists of multiple small granulomas composed of multinucleated cells containing birefringent crystals, which are identified in the alveolar septa and alveolar air spaces. In long-standing disease the nodules tend to confluence, producing large foci of consolidation associated with progressive fibrosis, resembling the progressive massive fibrosis seen in other pneumoconiosis. Panacinar emphysema, sometimes with bulla formation, is often evident. Foreign material is readily identifiable within the giant cells and is particularly well seen by polarization microscopy.4,7
IODINATED OIL EMBOLISM
Iatrogenic causes of iodinated oil embolism occur either after lymphangiography or after transcatheter oil chemoembolization. Chemoembolization of the liver for unresectable malignancy using ethiodized oil is being used with increasing frequency. Small and usually invisible intratumoral arteriovenous shunts allow chemoembolization material to pass into the hepatic veins and thence into the lungs. Although ethiodized oil may cause pulmonary inflammatory changes, most patients with iodinated oil embolism are asymptomatic. Rarely, cough, dyspnea, and hypotension occur. Extrahepatic chemoembolization material is commonly seen in other organs, but usually do not cause problems.1,8
CT findings consist of multifocal patchy areas of ground-glass attenuation and high-attenuation areas of consolidation and collapse (Fig. 5).
Pulmonary tuberculosis is a chronic recurrent infection caused by Mycobacterium tuberculosis. Symptoms are most commonly nonspecific, and include fatigue, weakness, anorexia, weight loss, and mild fever. Unproductive or mildly productive cough is usual, occasionally associated with hemoptysis.4
The patients with tuberculosis may present on CT scans focal areas of air-space consolidation, which could cavitate. Ill-defined centrilobular branching nodules may be seen, assuming the so called tree-in-bud pattern.4 Dystrophic calcifications are frequently seen in chest tuberculosis, being related to pulmonary granulomas, mediastinal lymph nodes, and irregular fibrotic lung lesions. Eventually, early inflammation with caseous formation presents higher phosphatase activity inside the necrotic foci, which invariably calcify9 (Fig. 6).
At histology, the initial reaction presents as an alveolar exudate composed by edema, fibrin, and polymorphonuclear leukocytes. Later, the mononuclear cells replace the former histologic pattern, presenting predominantly as necrotizing and non-necrotizing granulomas. These lesions may become confluent, resulting in the formation of necrotic areas containing the causal agents inside them. Larger portions of the pulmonary parenchyma are progressively affected as the disease evolves, being characterized by inflammatory and necrotic lesions. Caseous, necrotic, and fibrotic areas may present further dystrophic calcification.4
Silicoproteinosis is related to heavy exposure to silica dust, which evolves as a rapidly progressive disease. This abnormality results in air spaces filled by proteinaceous material similar to that seen in idiopathic alveolar proteinosis. The disease develops over a period of a few months to 1 year, in individuals exposed to dust with high concentration of silica, especially sandblasters. These patients had rapidly progressive shortness of breath and presents high rate of mortality in the first year after the onset of symptoms.10
HRCT of the lung shows ill-defined centrilobular nodules, bilateral ground-glass opacities, and bilateral areas of air-space consolidation. Nodular calcifications are common findings in this subject, usually presenting a punctuate pattern within the areas of consolidation10 (Fig. 7).
The classic pathologic finding is deposition of periodic acid-Schiff–positive proteinaceous material within the air spaces. In contrast to chronical exposure to silica-containing dust, silicoproteinosis presents minimal collagen deposition and fibrosis.4,10
Pulmonary amyloidosis is a rare disease presenting 3 forms: submucosal deposits in the airways (tracheobronchial form), parenchymal nodules (nodular parenchymal form), or diffuse interstitial damage (diffuse parenchymal or alveolar septal form).1,3 Diffuse parenchymal amyloidosis is the least common form of this disease, but the most clinically significant, assuming higher association to systemic amyloidosis than to localized one.3,4 Patients with this form are prone to die of respiratory failure, and most common symptoms are related to progressive dyspnea.11
HRCT abnormalities consist of abnormal reticular opacities, interlobular septal thickening, multiple small nodules, and air-space consolidation.1,3,4 The diffuse parenchymal pattern is mostly nodular, although confluent consolidations may be seen. Basal and peripheral distribution is the dominant aspect.4 Lymph node enlargement, and unilateral or bilateral pleural effusions are associated findings.4 Nodules and areas of consolidations could show calcifications, some of them with punctate aspect3,11 (Fig. 8).
Histologically, amyloid is a proteinaceous material collecting alongside the pulmonary interstitium, the media of small blood vessels, and the endothelial and epithelial basal membranes, usually assuming a uniform linear or micronodular appearance.11 Foci of calcification inside consolidations and small amyloid nodules can be found in pathologic specimens. Eventually, osseous metaplasia are seen in the calcified areas.3,4
Air-space consolidations can be seen in a wide variety of diseases affecting the lungs. The identification of consolidation with diffuse of focal high attenuation narrows the differential diagnosis. The most common causes of diffuse hyperdense consolidations are MPC, PAM, amiodarone lung toxicity, talcosis, and deposition of iodinated oil material. Consolidations with punctate calcifications suggest as differential diagnosis tuberculosis, silicoproteinosis, and parenchymal amyloidosis. The association of consolidation with high attenuation, clinical presentation, and additional CT findings could narrow even more the differential diagnosis (Table 1) avoiding, in some cases, invasive procedures, such as pulmonary biopsy.
Consolidations with diffuse or focal high attenuation can result from a variety of different conditions. We have presented a diagnostic approach based on appearance and distribution of these lesions. Despite the limitations, we believe that the proposed diagnostic approach can be helpful in the differential diagnosis of the various conditions that result in consolidations with high attenuation of the pulmonary parenchyma.