Case #12 Discussion:

Differential diagnosis for a solitary pulmonary nodule (SPN):

A round opacity on a chest film may be a solitary pulmonary nodule, but it is essential to rule out multiple lesions, lesions of the skin, subcutaneous tissue, and Aab. The basic concern here is differentiating between benign and malignant masses. Benign tumors tend to be small, spherical , and have smooth margins. Calcification is associated with benign lesions: Diffuse, central, laminar, or multiple large areas of calcification are typically seen with benign tumors, whereas eccentric or stippled internal calcifications occur in both malignant and benign lesions. Spiculated margins, rapid growth, large size, and intense enhancement with contrast are characteristics of malignant tumors. In a smoker of advanced age it is essential to aggressively rule out malignancy. Of course clinical data will help in ranking alternative diagnoses.

(1) Lung cancer:

• Bronchogenic carcinoma-- most likely cause of SPN in an elderly smoker, peaks at age 55-65 y/o.
• Metastasis-- common but no known primary in this case, usually multiple, but some may be too small to detect on radiograph, thus requiring CT scan to visualize.
• Lymphoma-- possible, but rarely presents as SPN
• Pulmonary blastoma-- rare, usually seen in children/young adults
• Leiomyosarcoma

(2) Benign lesion: (less than 5% of all primary lung tumors)

• Bronchial adenoma: 70-80% of all benign pulmonary nodules, often in central location
• Carcinoids (80-90%); adenocystic (10-15%), mucoepidermoid (2-3%) (Carcinoid tumor-- related to small cell lung cancer (both are Kulchitsky cell-derived); expect associated carcinoid syndrome secondary to production of amines/peptides)
• Pulmonary hamartoma: Accounts for 5% of all SPNs, peaks at age 60 (M>F), fairly slow-growing, and 30% are calcified
• Leiomyoma/ Fibroma/ Neurofibroma/ Lipoma/ Hemangioma/ Chondroma/ Teratoma/ Pseudolymphoma
• These benign neoplasms all very uncommon and usually occur in a central/ tracheobronchial location. They are unlikely diagnoses in this case.
• Granular cell myoblastoma

Factors that favor pursuing histologic diagnosis in this case:

• h/o tobacco use age-- absolute indication
• > 35 y/o -- absolute indication
• lack of calcifications
• chest symptoms (posterior shoulder pain in this case)
• rapid growth

Outcome:

A lung biopsy was complicated by a pneumothorax (#2). The pneumothorax was reduced by chest tube placement. Histological analysis revealed small cell bronchogenic carcinoma and the tumor was subsequently resected.