Pulmonary Tumor Embolism

Pathology and Pathogenesis

Tumor emboli are common in the lungs. A few of them survive to form metastatic deposits but most die very soon after arriving in the lungs: the embolus then becomes enclosed by platelets and finally undergoes organization. Occlusion of the pulmonary arteries may be due to tumor alone, or the tumor may promote thrombosis, organization of which results in fibrocellular intimal thickening, the so-called carcinomatous thrombotic microangiopathy (tumor thrombotic microangiopathy, TTM) or vascular intimal carcinomatosis [33].

Symptoms and Signs

The most common presenting complaint is dyspnea, in 57–100 % of cases [34]. Clinical symptoms and signs of pulmonary tumor embolism include subacute and progressive dyspnea, tachypnea, tachycardia, and hypoxemia. Right heart failure is present in 15–20 % of cases.

CT Findings

CT findings of pulmonary tumor embolism include peripheral wedge-shaped opacity, filling defects in the central pulmonary arteries, dilated and beaded peripheral pulmonary arteries, and nodular and branching centrilobular small nodules (tree-in-bud pattern) [35, 36] (Fig. 18.8).

CT–Pathology Comparisons

Vascular tree-in-bud sign are caused by the filling of centrilobular arteries with tumor cells themselves or thrombotic microangiopathy characterized by extensive fibrocellular intimal hyperplasia of small pulmonary arteries initiated by tumor microemboli [35]. Dilated and beaded peripheral pulmonary arteries reflect intravascular tumor emboli or microangiopathy (fibrocellular intimal hyperplasia) [36]. Peripheral wedge-shaped opacity distal to some of the dilated pulmonary arteries suggests pulmonary infarct.

Patient Prognosis

There is no specific treatment if pulmonary tumor embolism is diagnosed antemortem. There have been case reports of survival if the tumor is highly responsive to chemotherapy (e.g., choriocarcinoma, Wilms’ tumor, renal cell carcinoma, gastric cancer) [37].

Small Nodules with Perilymphatic

Distribution

Definition

Small nodules are considered perilymphatic when the nodules are predominant in relation to the subpleural location, interlobular septa, and centrilobular core structures as well. The nodules may be observed along the parahilar bronchovascular bundles [1]. The distinction between perilymphatic and random distribution is usually determined by observing patchy versus random and the presence of thickening or nodularity of the bronchovascular bundles (Fig. 18.9). Namely, the patchy distribution and the presence of interstitial thickening or nodularity favor the decision of perilymphatic distribution, whereas random distribution and normal or smooth bronchovascular bundles suggest random distribution [2].

Diseases Causing the Pattern

Perilymphatic small nodules are observed in patients with pneumoconiosis (Fig. 18.10), pulmonary sarcoidosis

(Figs. 18.9 and 18.11), lymphangitic carcinomatosis, and pulmonary alveoloseptal amyloidosis [1] (Fig. 18.12).

Distribution

In pneumoconiosis, small nodules show upper and middle lung zone predominance. Also in sarcoidosis, the lesions usually show upper and middle lung zone predominance but may show no zonal predominance. Lymphangitic carcinomatosis demonstrates middle and lower lung zone predominance as is the case in amyloidosis [38].

Clinical Considerations

The presence of occupational exposure history to coal dusts or silica renders a diagnosis of pneumoconiosis. Patients with pulmonary sarcoidosis usually have no specific symptoms. The disease may be suspected with abnormal chest radiographs. Conversely patients with pulmonary sarcoidosis may have fatigue, fever, weight loss, dry cough, or shortness of breath. Up to 20 % of individuals with sarcoidosis develop skin problems such as rash or nodules. Eye symptoms such as blurred vision, pain, and photosensitivity may occur occasionally in sarcoidosis. The most common primary cancer sites related to PLC are the breasts, lungs, colon, and the stomach [39].