MRI of the lungs in neoplasms

MRI techniques in pulmonary oncology

The standard protocol for evaluating pulmonary neoplasms includes acquiring T1- and T2-weighted images in three mutually perpendicular planes. A critical requirement is synchronizing the scan with the patient's breathing to avoid motion artifacts.

To address complex diagnostic challenges, supplementary techniques are widely used:

• Dynamic contrast-enhanced MRI: used for detailed study of pulmonary nodule characteristics and assessment of their vascularity.
• Diffusion-weighted imaging (DWI): provides the ability to clearly differentiate the tumor itself from the surrounding intact lung parenchyma. In addition, this sequence allows for recording a positive tumor response to therapy even before overt changes in its physical dimensions occur.
• Dynamic cine MRI: an indispensable tool for assessing the degree of fixation of a peripheral tumor. The method allows dynamic visualization of whether the mass is fused with the chest wall or mediastinal structures.

Radiological semiotics of bronchogenic carcinoma

All radiological manifestations of intrathoracic bronchogenic carcinoma are conventionally divided into three main categories:

1. Signs of central tumors (which arise in a large bronchus directly at or near the lung root).
2. Signs of peripheral tumors.
3. Assessment of the staging of intrathoracic spread of the malignant process.

Peripheral tumors deserve special attention. About 40% of all bronchogenic carcinomas develop distal to the level of the segmental bronchi. Notably, in approximately 30% of clinical cases, the presence of a peripheral mass is the sole radiological finding, which requires a thorough analysis of its structure and contours.

Evaluation of the shape and contours of a peripheral nodule

The specific location of certain masses can complicate diagnosis. For example, superior sulcus tumors (Pancoast tumors, Pancoast tumors) can visually strongly resemble benign apical pleural thickening.

In general, most peripheral lung cancers assume an approximately spherical or oval shape. Perfectly spherical nodules with sharp and smooth margins are extremely rare. Much more frequently, the following changes are observed:

• Lobulation: a very common radiological sign indicating uneven growth rates of different parts of the neoplasm. On a standard radiograph, this sign may present as a characteristic notch along the margin of the nodule.
• Corona radiata sign: manifests as numerous fine strands (spiculated margins) radiating from the central mass deep into the lung tissue. Sometimes areas of translucent parenchyma are visible between these strands. Although the sign is not 100% specific, it indicates with a very high probability that the carcinoma is infiltrating the adjacent lung.
• Pleural tail: a linear shadow stretched between the peripheral mass and the pleura. It also occurs in benign diseases. In cancer, this strand most likely represents either an area of discoid atelectasis (arising from obstruction of a small bronchus distal to the tumor) or pronounced edema of the interlobular septa against the background of local lymphatic obstruction.

Dumbbell-shaped tumor configurations or two adjacent isolated nodules growing close to each other are occasionally encountered. It is also worth remembering that, despite typically well-defined margins, some peripheral cancers (especially certain histological types of adenocarcinoma) have indistinct contours that a radiologist might mistakenly attribute to focal pneumonia-like consolidation.

Tumor cavitation and calcification

The process of cavity formation (cavitation) can be detected in tumors of absolutely any size and is best visualized using computed tomography. Among all histological variants, squamous cell carcinoma (squamous cell carcinoma) is the most prone to breakdown and cavity formation.

The wall of such a cavity usually has uneven thickness (typically 8 mm or more). Air-fluid levels are frequently identified inside the cavity. The inner contour may contain lobulated tumor nodules, although sometimes the wall retains smooth inner and outer outlines.

Regarding calcification, it is rarely visible on a plain chest radiograph within a bronchogenic carcinoma, but on CT it is detected in 6–10% of cases. There are two main reasons for the appearance of calcifications:

1. Enulfment of pre-existing old calcified granulomas (granulomatous foci remaining after previous infections) by the actively growing tumor.
2. Dystrophic calcification of the tumor tissue itself. On images, this appears as amorphous or cloud-like calcification (this variant occurs in less than 10% of cases).

Class and exam questions

What else to study on this topic

• MR semiotics of central bronchogenic carcinomas.
• Differential diagnosis of Pancoast tumors and benign apical pleural thickening.
• The role of imaging methods in staging the intrathoracic spread of malignant processes.
• Causes of pleural tail formation in benign diseases.
• Imaging features of adenocarcinomas with indistinct contours (mimicking pneumonia).

Other topics in the «Chest Radiology» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.