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Solitary Pulmonary
Nodule
Topic of the week
An SPN is defined as a single, discrete pulmonary
opacity that is less than 3 cm in diameter, surrounded
by normal lung tissue, and not associated with
adenopathy or atelectasis.Generally, a pulmonary nodule
must reach 1cm in diameter before it can be identified
on a chest radiograph.
Causes :
SPNs may have the following causes :
• Neoplastic (malignant or benign)
o Bronchogenic carcinoma
o Metastasis
o Lymphoma
o Carcinoid
o Hamartoma
o Connective Tissue and neural tumors – Fibroma,
neurofibroma, blastoma, sarcoma
• Inflammatory (infectious)
o Granuloma – TB, histoplasmosis, coccidioidomycosis,
blastomycosis, cryptococcosis, nocardiosis
o Lung abscess
o Round pneumonia
o Hydatid cyst
• Inflammatory (noninfectious)
o Rheumatoid arthritis
o Wegener granulomatosis
o Sarcoidosis
o Lipoid pneumonia
• Congenital
o Arteriovenous malformation
o Sequestration
o Lung cyst
• Miscellaneous
o Pulmonary infarct
o Round atelectasis
o Mucoid impaction
o Progressive massive fibrosis
Imaging Studies :
1. Chest Radiography
a. Because SPNs are first detected on chest radiographs,
the initial decision is whether the nodule is pulmonary
or extrapulmonary in nature. Findings from a lateral
chest radiograph, fluoroscopy, or CT scan may help
confirm the location of the nodule.
b. Radiologic characteristics that may help establish
the diagnosis with reasonable certainty include :
i. Size and shape : Corona radiate (numerous strands
radiating into the surrounding lung) may indicate a
bronchogenic carcinoma. A well-defined, smooth,
nonlobulated edge may indicate a benign lesion.
ii. Rate of Growth : Doubling time of a nodule.
Bronchogenic carcinoma generally doubles in 1-18 months.
Doubling times of less than 1 month suggest infections;
doubling times of more than 18 months suggest benign
processes such as granuloma, hamartoma, bronchial
carcinoid and rounded atelectasis.
iii. Calcification : A stippled or eccentric pattern is
associated with malignancy. Dense central or concentric
calcification suggests benign lesions.
2. Computed Tomography
a. Detection of nodules as small as 3-4 mm.
b. CT densitometry measures the attenuation coefficients
of a lesion. A value of more than 185HU has been
suggested as a cutoff for benign lesions.
c. Demonstration of fat within a nodule. This is
specific for a benign lesion.
d. CT halo sign, ie, ground-glass attenuation
surrounding a nodule on CT scan image, most commonly
indicates infection with an invasive Aspergillus
species.
3. Positron emission tomography
a. Sensitivity of fluorodeoxyglucose (FDG) positron
emission tomography (PET) scan to be more than 90%, with
a specificity of more than 90%.
4. Biopsy
a. Biopsy of an SPN can be performed bronchoscopically
or via transthoracic needle aspiration (TTNA).
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