Classification principles and features of various tumors
In modern clinical practice, the foundation for determining the stage of non-small cell lung cancer (НМРЛ / NSCLC) is the 8th edition of the TNM system. The stage of the disease (from IA to IVB) is determined by a combination of tumor parameters (from T1 to T4), lymph node status (N0–N3), and the presence of metastases (M1a–M1c).
For small cell lung cancer (МРЛ / SCLC), the TNM system is also applicable; however, a binary division is more commonly used to select treatment tactics:
- Limited disease: the process does not extend beyond a single hemithorax. Involvement of contralateral lymph nodes (mediastinal, supraclavicular) and the presence of a malignant pleural effusion are permitted.
- Extensive disease: tumor involvement extends beyond the anatomical boundaries specified above.
Bronchopulmonary carcinoids (neuroendocrine tumors of varying malignancy grades) are staged according to the same TNM rules as non-small cell carcinoma.
Diagnostic imaging protocols
Although standard radiography remains the primary screening examination, its resolution is extremely limited. The gold standard for staging is multislice computed tomography (64 slices or more).
The optimal CT protocol involves a submillimeter slice thickness, a single breath-hold scan, and intravenous contrast enhancement. Contrast is omitted only in cases of strict contraindications (bronchial asthma, renal failure, allergy). Positron emission tomography (PET/CT) and magnetic resonance imaging (MRI) serve as adjunctive modalities used in complex clinical scenarios.
Assessment of the primary tumor (T) and local invasion
Topographically, carcinomas are generally divided into central and peripheral. Central lesions frequently cause widening of the lung root and bronchial obstruction. This leads to post-obstructive atelectasis and consolidation, which can mask the true size of the tumor node. The accumulation of infected secretions distal to the obstruction creates the picture of a drowned lobe.
A critically important aspect of T-staging is the evaluation of invasion into adjacent structures:
- Mediastinal invasion: confirming invasion on CT is challenging. According to Glazer's criteria, a tumor is highly likely to be resectable if the length of its contact with the mediastinum does not exceed 3 cm, it encases the aorta by less than 90 degrees, and a fat plane is visualized between the node and mediastinal structures.
- Chest wall invasion: manifests as localized pain syndrome. Reliable CT signs include bone destruction and the appearance of an extrapleural soft tissue component. The disappearance of the extrapleural fat layer is a concerning, but not 100%, sign.
Lymph node (N) and metastasis (M) staging
The evaluation of lymph node involvement on CT and MRI is based primarily on their size. The universally accepted threshold is a transverse dimension (short axis) of 10 mm. Nodes exceeding this value are considered pathological.
However, this criterion has significant limitations:
- False-positive results: lymph node enlargement is frequently of an inflammatory or reactive nature (especially in post-obstructive pneumonia, prior tuberculosis, or sarcoidosis).
- False-negative results: normal-sized lymph nodes may harbor micrometastases.
To detect distant metastases (M-status), 18F-FDG PET/CT is most effective, allowing the assessment of the spread of the process to soft tissues and bones. Radioisotope bone scintigraphy is used as an alternative for detecting bone lesions.
Briefly: answers to topical questions
What are the absolute contraindications to the administration of contrast media in chest CT?
Computed tomography protocols indicate the following contraindications to intravenous contrast administration:
- Renal impairment.
- Allergy or previous reactions to contrast media.
- Asthma.
- Difficult venous access.
Criteria for the absence of mediastinal invasion (according to Glazer): the "3–90–fat" rule (contact with structures less than 3 cm, aortic encasement less than 90°, visible fat plane).
Class and exam questions
What size of an intrathoracic lymph node is considered a sign of metastatic involvement?
In diagnostic imaging, a lymph node size of greater than 10 mm on the short axis is considered pathological. However, this criterion is not absolute due to potential inflammatory reactions and micrometastases.
How to differentiate a central tumor from concomitant pneumonia?
Post-obstructive pneumonia persists for more than 2–3 weeks, accompanied by volume loss of the lobe and the absence of the air bronchogram sign. On CT, the obstructing node within the bronchial lumen can often be directly visualized.
What is the Golden S-sign?
This is a radiological phenomenon of interlobar fissure displacement. It occurs because a bulky central tumor prevents the uniform physiological displacement of the fissure during lobar atelectasis.
What else to study on this topic
- Radiological patterns: calcification, ground-glass opacity, pseudocavitation
- The spectrum of pulmonary neuroendocrine tumors and DIPNECH
- Differential diagnosis of peripheral carcinoid and carcinoma
- Complications of central tumors: bronchocele, mucocele, lung abscess
- The role of specialized MRI sequences (STIR) in lymph node evaluation
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