Solitary pulmonary nodule / mass

Causes of solitary pulmonary lesions

A wide range of pathologies can present as a solitary nodule or mass. They can be divided into several main categories, although the radiological picture is often nonspecific:

• Malignant and benign tumors: bronchogenic carcinoma (bronchial carcinoma), bronchial carcinoid (bronchial carcinoid), solitary metastasis, hamartoma (hamartoma).
• Inflammatory and infectious processes: chronic pneumonia, abscess, granuloma (granuloma), fungal ball or mycetoma (fungus ball).
• Vascular lesions: pulmonary infarction, arteriovenous malformation (arteriovenous malformation).
• Congenital and acquired anomalies: bronchogenic cyst, sequestration (sequestration), bronchocele (bronchocele).
• Other conditions: echinococcal cyst, pulmonary hematoma, progressive massive fibrosis in coal miners (massive fibrosis in coal workers).

It should be remembered that there are no specific X-ray or CT signs that allow one to distinguish one benign neoplasm from another (or from a malignancy) with absolute certainty. The characteristics of the shadow depend solely on the location and size of the pathological focus.

Pseudolesions (mimics)

When analyzing radiographs or tomograms, it is important to exclude so-called mimics (mimics)—structures that project onto the lung fields and create the illusion of an intrapulmonary nodule. These include:

1. Extrathoracic artifacts (external objects).
2. Skin lesions of the trunk.
3. Lesions of the thoracic bone structures.
4. Pleural tumors or pleural plaques.
5. Encysted pleural fluid (encysted pleural fluid).
6. Large pulmonary vessels (especially in orthogonal projection).

Characteristics of specific benign neoplasms

Despite the similarity of many nodules, certain tumors have their own clinical and radiological nuances:

• Pulmonary hamartoma: usually a round, completely smooth lesion. Most often asymptomatic. A specific (though not always present) imaging sign is coarse "popcorn" calcification (coarse popcorn calcification).
• Leiomyoma (leiomyoma): the solitary variant is indistinguishable from other tumors. However, there is a form of benign metastasizing leiomyoma, which presents as multiple separate nodules. In women, these may be extremely slow-growing metastases of uterine leiomyoma (a history of hysterectomy is often present).
• Intrapulmonary teratomas: extremely rare, predominantly benign lobulated masses (lobulated masses). Their structure may contain areas of calcification or cavitation (cavitation).
• Sclerosing hemangioma: an asymptomatic solitary benign lesion that sometimes demonstrates visible calcification.
• Squamous papillomas: occur in the trachea, bronchi, and lungs (rarely). They present as multiple, well-defined, round nodules prone to cavitation. The condition is closely associated with juvenile onset recurrent respiratory papillomatosis caused by the human papillomavirus (HPV).

Inflammatory myofibroblastic tumor (IMT)

This lesion has numerous synonyms: plasma cell granuloma, inflammatory pseudotumor, fibrous histiocytoma. The pathogenesis of IMT remains incompletely understood—it may represent a reactive inflammatory tissue, a locally invasive process, or a low-grade malignant tumor (low-grade malignancy).

The disease can occur at any age, but it is one of the most frequent primary pulmonary tumors in pediatric practice. Clinically, it is usually an asymptomatic nodule that may develop calcification and cavitation. An important feature is that these tumors are PET-positive, which allows them to masterfully mimic bronchogenic carcinoma. Similar lesions can also form in other organs.

Benign lymphoproliferative disorders

These rare conditions may also manifest with characteristic imaging findings in the parenchyma:

• Lymphocytic interstitial pneumonia (LIP): diffuse infiltration of the interstitium by lymphocytes. Histologically, it is very difficult to differentiate from low-grade lymphoma. As an isolated disease, it is rare; it is much more frequently associated with immunological disorders—AIDS and Sjögren's syndrome. CT scans reveal bilateral areas of ground-glass opacification (ground-glass opacification) and thin-walled cysts.
• Follicular bronchiolitis: diffuse hyperplasia of MALT (mucosa-associated lymphoid tissue). Imaging shows reticular opacities, centrilobular nodules, bronchial wall thickening, airway dilation, and peribronchovascular consolidation.

Class and exam questions

What else to study on this topic

• Radiological criteria for the differential diagnosis of bronchogenic carcinoma and solitary metastasis.
• Imaging features of arteriovenous malformations and pulmonary infarction.
• The role of PET-CT in diagnosing PET-positive pseudotumors and carcinomas.
• Imaging patterns of idiopathic interstitial pneumonias, including LIP.

Other topics in the «Chest Radiology» section

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