Benign granuloma: This is often the most common cause of small, pleural-based nodules, especially if the patient has a history of exposure to tuberculosis or histoplasmosis, or if the nodule has been stable or slowly growing over time.

Malignancy (e.g., metastasis or primary lung cancer): Although less common for such a small size, any new or growing nodule, especially one that is pleural-based, warrants consideration of malignancy, particularly in patients with a history of cancer or significant smoking history.
Intrapulmonary lymph node: These can present as small, pleural-based nodules and are generally benign.
Hamartoma: A benign lung tumor that can appear as a small nodule, though typically they have characteristic popcorn calcification or fat within them on imaging.

Pulmonary metastasis: Even if the patient has no known primary cancer, a new or growing nodule could be a metastasis from an unknown or undiagnosed primary tumor.
Primary lung cancer: Early detection of lung cancer can significantly improve prognosis, making it crucial not to miss, even in smaller nodules.
Infectious causes (e.g., abscess or fungal infection): Although less likely for a small, pleural-based nodule, infectious causes can be serious and require prompt treatment.

Pulmonary arteriovenous malformation (AVM): These are abnormal connections between veins and arteries in the lung and can appear as nodules on imaging.
Amyloidosis: Can cause nodular lung lesions, though this is less common and usually associated with other systemic symptoms.
Lymphangitic carcinomatosis: Involvement of the lymphatic vessels of the lung by malignancy, which can cause nodular lesions, though typically more diffuse and associated with other findings.