Pulmonary arterial sarcoma (PAS) is a rare and highly malignant tumor of the great vessels(1) that is often diagnosed after surgery or at autopsy(5). Histologic examination shows that pulmonary artery sarcoma is most often undifferentiated (30%)(6). In general, PAS arises in multifunctional cells in the subendothelial layer(7). Such tumors are characterized by restricted growth in the lumen, with less infiltration of the lung parenchyma and little capacity to metastasize. However, the prognosis is extremely poor(7), especially in patients without surgical resection, whose median survival time is 1.5 months(8). Most patients with PAS have no obvious symptoms in the early stages and then present with symptoms related to pulmonary hypertension(7), including dyspnea, chest pain, cough and syncope, as observed in the present case. The initial diagnosis of this young patient was pulmonary hypertension. In general, acute pulmonary hypertension occurs when dislodged clots from deep veins of the lower extremities block the proximal pulmonary circulation embolization of the pulmonary circulation(9). Venous thrombosis is a common complication of malignancy, and patients presenting with distant metastases are at higher risk of developing venous thrombosis(10). However, in some rare cases, patients with pulmonary artery sarcomas cause direct damage to the vascular endothelium and experience recurrent thromboembolism despite aggressive anticoagulation and thrombolytic therapy, which in turn leads to persistent pulmonary hypertension(11). Except for atypical clinical manifestations caused by pulmonary hypertension, PAS has an insidious onset. Therefore, it is easily misdiagnosed as any cause of obstructive pulmonary hypertension, such as pulmonary embolism, lung cancer involving the pulmonary arteries, and pulmonary tumor embolism from various malignancies. All these factors often lead to delayed diagnosis for 4 months.
In this case, the delayed diagnosis can be the result of patient-related, sarcoma-related, or radiologist-related factors. First, when pulmonary hypertension was found in a young male with no specific medical history, idiopathic pulmonary hypertension is usually the only consideration but missed other possible diseases. Meanwhile, the strong cardiopulmonary compensation of young men hides the early signs of right heart failure. By the time significant symptoms developed, the tumor had extended widely. Persistently elevated D-dimer causes doctors to miss tumors. Second, based on its location and growth pattern, there are nonspecific manifestations, and it is difficult to obtain a tissue sample from this hard-to-access lesion to confirm the diagnosis. The results of routine serum tumor-related markers are also not effective in suggesting the presence of a tumor, so even if the doctor suspects malignancy, it is difficult to find evidence in routine tests. The inaccessible location also makes it difficult to obtain tissue samples. Routine serum tumor-related marker tests cannot effectively suggest the presence of a sarcoma, so even if the doctor suspects malignancy, it is difficult to find evidence on routine tests. In addition, radiologists may suffer interference from stereotypical thinking. Radiologists have limited knowledge of PAS’s imaging features, as they are extremely rare, so they cannot find this differential diagnosis for the clinic at an early stage. Additionally, the scanning process of CTPA is fixed and usually lacks delayed-phase images, which usually miss the sign of enhancement in the lesion.
Although the tumor is not detected by imaging manifestations in time, the final PAS diagnosis was detected relying on imaging manifestations and clinical presentation, supplemented by pathologic findings of brain metastases. In most PAS cases, the CT manifestations are similar to pulmonary embolisms, and there is no significant enhancement in CTPA(12). However, there are other features: (1) the low-density mass almost completely occupies the main pulmonary artery trunk and spreads proximally to involve the pulmonary valve and right ventricle(13); (2) PAS originates from the wall of the pulmonary artery, eclipsing at least one wall of the pulmonary trunk and forming the wall eclipsing sign(14); (3) the filling defects often show lumen-like casts instead of linear-shaped embolism caused by acute pulmonary disease(7); and (4) the mass causes dilatation of the artery, while lung cancer invading the arteries causes lumen occlusion. In addition, in our patient, the mass showed marked inhomogeneous enhancement during the delayed phase of PCTA(13). 18F-FDG PET-CT is the most reliable method to differentiate between PAS and pulmonary thromboembolism, which has a significantly higher FDG uptake than thrombotic lesions due to the high metabolism of the tumor cells(15), which was clearly differentiated from pulmonary embolism. PAS is also uniquely demonstrated on enhanced MRI(16), but many patients have difficulty holding their breath for a prolonged time to comply with MRI scans(17). Therefore, we should note that CTPA, which is commonly used in patients with dyspnea, is most relevant for the early diagnosis of PAS.
The described case reveals the possibility of multiple metastases of PAS and analyzes the reasons for delayed diagnosis in such cases. Radiologists should be cognizant of the imaging manifestations of PAS and raise suspicion as early as possible in patients with severe dyspnea and pulmonary arterial trunk filling defects.