Discussion
Diagnosis With Brief Discussion
- Diagnosis
- Lung parenchymal amyloidosis
- Radiologic Findings
- Fig 1. Chest AP shows multiple lung nodules disseminated in the bilateral lung parenchyma.
Fig 2-4. CT scans show multiple variable-shaped lung nodules in the bilateral lung parenchyma. The nodules occur most in the lower lobes and periphery. In the mediastinal window setting, several lung nodules have internal calcifications or cavitations.
- Brief Review
- Amyloidosis, a disorder of protein folding, is rare. It affects the respiratory tract in about 50% of cases. The most important proteins associated with respiratory tract disease are amyloid L and amyloid A.
There are three major forms of amyloidosis in the lower respiratory tract: tracheobronchial, nodular parenchymal, and diffuse parenchymal (alveolar septal, interstitial). The parenchymal nodules of localized pulmonary amyloid can be solitary or multiple and are usually fairly well-defined. Amyloid is often identifiable in the alveolar interstitium at the periphery of the nodule.
Pulmonary function tests may show evidence of restriction and impaired gas transfer in patients who have diffuse alveolar septal amyloidosis and air-trapping and fixed upper airway obstruction in those who have proximal tracheobronchial involvement.
In CT images, nodular primary parenchymal amyloidosis manifests as solitary or, less commonly, multiple nodules usually ranging from 0.5 to 5 cm in diameter. On occasion, nodular parenchymal amyloidosis may result in a large mass. Calcification is seldom evident on radiographs but is seen in 20% to 50% of nodules on CT. The nodules tend to be more common in the periphery of the lower lobes but may be seen anywhere in the parenchyma. Rarely, nodules cavitate. Cysts may occasionally be present adjacent to the nodules. Cysts and nodular amyloid deposits have been described most commonly in patients with Sjögren syndrome, with or without associated lymphoid interstitial pneumonia. The main differential diagnosis of the parenchymal nodular form of amyloidosis is granulomatous infection or primary or metastatic tumors.
The diagnosis of amyloidosis usually requires histologic confirmation. The diagnosis is based on demonstration of amyloid by Congo red staining, which produces characteristic apple-green birefringence under crossed polarized light. Nodular parenchymal amyloidosis is usually asymptomatic and remains stationary or progresses slowly. It usually has a good prognosis and seldom requires treatment.
- References
- 1. Christopher M. Walker, Jonathan H. Chung. Imaging of the Chest, 2nd Edition. Chapter 38. Metabolic and Storage Lung Diseases.
- Keywords