General radiological picture and radiography
Changes in lymphangitic carcinomatosis may have either a central or peripheral predominance, affecting all zones of the lung parenchyma. Asymmetric involvement is also frequently encountered: the pathology may be limited to one lung or even a single lobe. Such an isolated pattern is particularly characteristic of lymphangitis associated with bronchogenic carcinoma.
Conventional chest radiography visualizes two main signs:
- Bilateral thickening of the so-called septal lines.
- Widespread nodulation (nodulation) against the background of the lung parenchyma.
Interestingly, the expected enlargement of the hilar lymph nodes (hilar lymph node enlargement) is far from a mandatory symptom and is detected in only a certain proportion of patients.
High-Resolution Computed Tomography (HRCT)
HRCT (HRCT) is the gold standard for a detailed assessment of interstitial changes. Carcinomatosis is characterized by the following complex of findings:
- Polygonal pattern: formed due to uneven thickening of the interlobular septa (interlobular septa).
- Bronchovascular bundle thickening: localized strictly in the center of the secondary pulmonary lobules.
- Discrete metastases: scattered pulmonary nodules within the parenchyma that often accompany lymphangitis.
- Focal opacities of the airspace.
- Peripheral wedge-shaped opacities: small subpleural structures that occur due to the volume-averaging effect against the background of significantly thickened septa.
When analyzing tomograms, the most important differential diagnosis is pulmonary edema. The key difference lies in the state of the lung tissue: in lymphangitic carcinomatosis, most acini adjacent to the thickened septa retain normal aeration (remain normally aerated).
Atypical forms of metastatic cancer
In addition to classic carcinomatosis, rarer metastasis patterns occur, each with its own radiological and clinical features.
- Endobronchial metastases (Endobronchial Metastases)
An extremely rare form in which tumor nodules grow in the submucosal layer of the bronchi. The primary site is most often melanoma, renal cell carcinoma, breast cancer, or colorectal cancer. The leading clinical and radiological sign in this case is the picture of airway obstruction.
- Miliary metastases (Miliary Metastases)
Manifested by multiple small nodules diffusely affecting both lungs. Visually, the picture is strikingly reminiscent of miliary tuberculosis. Unlike lymphangitic carcinomatosis, there are no large tumor masses or signs of lymphatic obstruction. This is the rarest cause of the miliary pattern, occurring in thyroid cancer, renal cancer, bone sarcomas, and choriocarcinoma.
- Tumor emboli (Tumour Emboli)
A rare complication occurring in gastric cancer, breast or prostate cancer, hepatic tumors (hepatocellular carcinoma), renal cancer, and choriocarcinoma. The mechanism involves the physical blockade of small branches of the pulmonary artery by tumor masses. Radiologically, this condition can lead to signs of pulmonary arterial hypertension.
Briefly: answers to topical questions
What are the exact pathogenetic pathways for tumor cells to enter the lymphatic vessels of the lungs in carcinomatosis?
The provided materials describe only general pathways of lymphogenic metastasis without specifics for pulmonary carcinomatosis. The entry of cells into the lymphatic bed occurs at the stage of intravasation.
- Intravasation — detachment of a malignant cell from the primary node, invasion into the wall of a lymphatic vessel, and entry into its lumen.
- Orthograde metastasis — spread of tumor cells along the natural lymph flow.
- Retrograde metastasis — movement of cells against the lymph flow.
After entering the lumen of the microvessel, the tumor embolus circulates in the lymph flow, followed by adhesion to the endothelial surface.
To differentiate miliary metastases from lymphangitic carcinomatosis, remember: "Miliary means small and without blocks" (no large nodes and no lymphatic obstruction).
Class and exam questions
Does lymphangitic carcinomatosis always cause enlargement of the hilar lymph nodes?
No, hilar lymphadenopathy is not a mandatory sign and is observed only in a fraction of patients.
How to reliably distinguish lymphangitic carcinomatosis from pulmonary edema on CT?
The main criterion is the state of the acini. In carcinomatosis, the lung tissue immediately adjacent to the thickened interlobular septa remains normally aerated.
Which tumors most frequently cause rare endobronchial metastases?
Such tumors include melanoma, renal cell carcinoma, colorectal cancer, and breast cancer.
How do miliary metastases differ from carcinomatosis?
In miliary metastases, there are no large nodes or signs of lymphatic obstruction, and the radiological picture visually mimics miliary tuberculosis.
What else to study on this topic
- Pathogenesis of tumor cell spread through lymphatic pathways
- HRCT semiotics of pulmonary edema for differential diagnosis
- Mechanisms of pulmonary hypertension development in tumor embolism
- Clinical features of endobronchial obstruction by metastases
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