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Figure
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History:
60 year old male smoker. 4 mm right
upper lobe pulmonary nodule on CT. The patient was referred to Main
Street Radiology for 6-month follow-up CT.
Findings:
Non-contrast Chest CT was performed on a 16-detector spiral CT. A
small right upper lobe nodule is seen on the routine 5mm image (figure
1), which is better appreciated on the high-resolution 0.75 mm image
(figure 2). 3D volumetric rendering of the nodule was also performed
(figure 3). The nodule measured 36 mm3 in volume, corresponding to 4.1
mm average diameter. This is unchanged since the prior exam,
compatible with a benign process.
Discussion:
Solitary pulmonary nodule (SPN) is a common finding in clinical
practice. These lesions whether found on conventional X-ray or CT scan
are usually benign, but a neoplastic process must be excluded,
especially in patients with risk factors for bronchogenic carcinoma.
Guidelines for evaluating SPNs are not clearly outlined, and opinions
vary greatly (AJR 2001; 176:1363-1369).
When a nodule is seen on X-ray, CT scan
of the chest should be performed, to exclude an artifact and to better
characterize the lesion. Lung nodules may appear calcified on
conventional X-ray, suggesting a benign diagnosis, which may eliminate
the need for a CT. However, it has been shown that determination of
presence of calcification in nodules on plain films is not reliable (AJR
2001; 176:201-204).
When performing a CT for pulmonary
nodules, high-resolution images should be performed, with slice
thickness of 1 mm or less, which will enable the Radiologist to
determine if the lesion is benign. If the lesion is non-specific in
appearance, 3D volumetric analysis produces more accurate measurement
of the lesion if follow-up studies are warranted. In a recently
published study (Radiology 2004; 231: 453-458), routine 2-dimensional
measurements were shown to be inaccurate for small nodules, with large
inter-observer and intra-observer variability. In a different study,
3D volumetric measurement of nodule size has been shown to be
significantly more accurate and reproducible (Radiology 2004;
231:446-452).
Considering the reproducibility of
volumetric measurement and growth rate of bronchogenic carcinoma,
mathematical analysis was performed to determine the appropriate time
interval for follow-up of pulmonary nodules (Radiology 2004;
231:446-452). 1-month follow-up was sufficient to detect change in 10
mm nodules, while 12 month follow-up was necessary for nodules less
than 3 mm. Using 2-dimensional measurements only, 12-month follow-up
was necessary for nodules less than 5 mm (Radiology 2004;
231:164-168).
Positron Emmision Tomography (PET) has
shown to be highly accurate for assessment of pulmonary nodules (JAMA
2001; 285:914-24), with sensitivity reported at 97%. PET scan should
be considered for all SPN greater that 8 mm.
Combining the volumetric spiral-CT and
PET data, the following table summarizes the general guidelines for
follow-up of SPN based on size:
| <3
mm |
12
month follow up CT |
| 3-5
mm |
6 month follow up CT |
| 5-8
mm |
3 month follow up CT |
| >
8mm |
PET |
|
At Main Street Radiology, we utilize a
3D-volumetric nodule-analysis software with our 16-detector spiral CT,
and we are the first facility in Queens to perform PET scans. With
these new technologies, we are best equipped to optimally evaluate
pulmonary nodules, significantly reducing the number of negative
biopsies and thoracotomies, while minimizing delay in diagnosis.
