Benign pleural tumors
Among benign neoplasms, fibromas and lipomas are the most frequently encountered.
- Benign pleural fibroma (Fibroma pleurae benignum): imaging shows a well-circumscribed, homogeneous lesion, often abutting the diaphragm. An important sign of extrapulmonary origin is the obtuse angle between the tumor and the chest wall. Large fibromas (especially greater than 10 cm) can displace the lung, cause atelectasis, establish collateral blood supply, and carry a risk of malignant transformation.
- Pleural lipoma (Lipoma pleurae): an asymptomatic, well-defined lesion of fat density. If heterogeneous soft-tissue components are detected on CT, liposarcoma should be suspected.
Malignant mesothelioma
A primary malignant tumor strictly associated with a history of asbestos exposure (which may be indicated by concomitant pleural plaques or asbestosis).
On radiographs, it appears as irregular, nodular pleural thickening, often accompanied by effusion. Computed tomography (CT) is effective for visualizing chest wall invasion and spread along the interlobar fissures, as well as for detecting enlarged lymph nodes (present in 50% of cases).
The prognosis depends on the histological subtype: the epithelioid variant has a more favorable prognosis than the sarcomatoid one. MRI is useful for differentiating the subtypes (the sarcomatoid subtype demonstrates lower ADC values on diffusion-weighted images), but a definitive diagnosis requires a biopsy.
Secondary (metastatic) tumors
These are the most common pleural tumors. They are typically adenocarcinomas originating from the ovaries, stomach, breast, or primary lung cancer.
Clinically and radiologically, they may present as a solitary nodule, multiple nodules, or diffuse pleural thickening. A characteristic companion is malignant pleural effusion. In cases of direct invasion by bronchogenic carcinoma (e.g., Pancoast tumor), rib destruction is a highly specific sign of invasion, while CT shows broad tumor contact with the pleura (greater than 3 cm) and the formation of an obtuse angle.
Role of PET/CT in imaging
Positron emission tomography (PET/CT) with fluorodeoxyglucose (FDG) is a key tool in pleural oncology.
It helps to:
- Distinguish benign lesions from malignant ones (due to high FDG uptake in the tumor).
- Select the optimal, most metabolically active target for biopsy.
- Assess lymph node status and detect extrathoracic metastases.
- Monitor the efficacy of chemotherapy.
Important to remember: False-positive results can occur in inflammation, infections, or following talc pleurodesis (FDG uptake persists for years). False-negative results occur with small tumor size, shallow depth of invasion, or low metabolic activity (epithelioid mesothelioma takes up the tracer less intensely than the sarcomatoid type).
Briefly: answers to topical questions
What histological subtypes of malignant pleural mesothelioma are distinguished?
Malignant pleural mesothelioma is classified into epithelioid, sarcomatoid, and biphasic histological subtypes.
- Epithelioid subtype (epithelioid subtype) — has a better prognosis, takes up FDG less intensely, and is characterized by higher apparent diffusion coefficient (ADC) values on MRI.
- Sarcomatoid subtype (sarcomatoid) — is distinguished by a worse prognosis, more intense FDG uptake on PET/CT, and significantly lower ADC values.
- Biphasic subtype — is characterized by a significant overlap of imaging features, which is why a biopsy is always necessary for accurate differentiation.
Class and exam questions
How to differentiate a pleural tumor from a lung tumor on CT/MRI?
Extrapulmonary lesions originating from the pleura (e.g., fibroma) form an obtuse angle with the chest wall, whereas intrapulmonary ones typically form an acute angle.
What is the purpose of dynamic contrast-enhanced MRI in mesothelioma?
It allows for the assessment of tumor perfusion, vascularization, and vascular permeability, which correlates with chemotherapy response and overall prognosis.
What is the value of PET/CT in pleural fibroma or lipoma?
Primarily to rule out malignant (sarcomatoid) transformation. Benign lipomas take up less FDG than the background level, whereas areas of malignant transformation will show increased uptake.
Is image guidance mandatory for pleural puncture?
Yes, all pleural punctures (and biopsies) should be performed under real-time ultrasound or CT guidance, which reduces the complication rate and increases the accuracy of tissue sampling.
What else to study on this topic
- MRI semiotics of malignant pleural lesions
- Features of talc pleurodesis on CT and PET
- Diffuse pleural involvement and pleural plaques in asbestosis
- Image-guided interventional procedures
- Tumor-like conditions (Erdheim-Chester disease, endometriosis)
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