Radiological Evaluation

Quit Smoking Magic

Quit Smoking Magic

Get Instant Access

Although an increasing number of solitary pulmonary opacities are diagnosed by computed tomography (CT), either incidentally or as part of lung cancer screening studies, many are still initially detected on chest radiographs. If the nodule is diffusely calcified (Fig. 3), or comparison with older radiographs shows stability in size for more than 2 years, the nodule is presumed to be benign and no further evaluation is recommended. Many nodules, however, require further radiological evaluation because (1) it can be difficult to determine whether a small nodule is calcified or stable in size on chest radiographs and (2) preexisting radiographs are often not available for review. Because up to 20% of small or subtle radiographical abnormalities thought to represent nodules are not within the lung, chest fluoroscopy, which is relatively inexpensive, is occasionally performed before CT [4]. Fluoroscopy often enables a determination of whether the opacity is in the lung (Fig. 4) and, by using a lower kilovolt peak (kVp) than conventional radiographical techniques, more optimally demonstrates calcification. However, fluoroscopy does not always enable confident determination of whether a radiographical abnormality is a

Rib Nodule

Figure 4 Rib fracture mimicking a pulmonary nodule. (A) Posteroanterior radiograph of right upper lung shows poorly marginated opacity overlying ribs (arrowheads). (B) Fluoroscopic view shows healing fracture of right anterior rib (arrowheads). Fluo-roscopy often allows a confident diagnosis, obviating the need for CT evaluation.

Figure 4 Rib fracture mimicking a pulmonary nodule. (A) Posteroanterior radiograph of right upper lung shows poorly marginated opacity overlying ribs (arrowheads). (B) Fluoroscopic view shows healing fracture of right anterior rib (arrowheads). Fluo-roscopy often allows a confident diagnosis, obviating the need for CT evaluation.

pulmonary nodule. CT is often performed to further evaluate these radiograph-ical abnormalities. CT is accurate in determining where the abnormality is located and, if in the lung, optimally evaluates morphological characteristics of the nodule (Fig. 5). CT is also useful in determining if the nodule is truly solitary and assessing for growth on serial studies. Interpretive difficulty, however, also occurs with CT. It can be difficult to determine whether a small opacity is a nodule, a vessel, or a pseudonodule due to partial volume averaging of adjacent intrathoracic structures. This difficulty can often be resolved by either increasing or decreasing the slice collimation. If standard 7-mm-slice collimation has been used, obtaining images through the region of abnormality using a slice collimation of 1 to 3 mm is useful in eliminating partial volume averaging. If 1- to 3-mm-slice collimation has been used (as is common in protocols utilized to evaluate the pulmonary arteries for emboli), the difficulty of differentiating a vessel from a small nodule is often overcome by reconstructing the original data at thicker collimation or by using maximal intensity projection (MIP) images (Fig. 6). Maximal intensity projection images are generated from an axial slab of volumetrical data obtained when spiral CT is performed. By displaying the continuity of vessels, this technique has been shown to improve nodule detection and discrimination from vessels [5]. Cine viewing of axial CT images at a workstation has also been shown to aid nodule detection and distinction of nodules from vessels [6].

Figure 5 Arteriovenous malformation (AVM) in woman with hereditary hemorrhagic telangiectasia. Chest radiograph (not shown) showed a small solitary nodule in lingula. Computed tomography reveals an enlarged feeding artery (arrows) and an enlarged draining vein (arrowheads) as well as the nidus of the vascular malformation (*). Morphologic characteristics are diagnostic for arteriovenous malformation. Computed tomography also revealed a few smaller AVMs in both lungs (not shown).

Figure 5 Arteriovenous malformation (AVM) in woman with hereditary hemorrhagic telangiectasia. Chest radiograph (not shown) showed a small solitary nodule in lingula. Computed tomography reveals an enlarged feeding artery (arrows) and an enlarged draining vein (arrowheads) as well as the nidus of the vascular malformation (*). Morphologic characteristics are diagnostic for arteriovenous malformation. Computed tomography also revealed a few smaller AVMs in both lungs (not shown).

A. Nodule Morphology

Evaluation of morphologic features, including size, margins, contour, and density, can be useful in determining whether a nodule is benign or malignant [7,8]. Although the likelihood of malignancy increases with increasing nodule size, widespread use and improvements in CT technology, coupled with a recent interest in CT screening for lung cancer, have resulted in the frequent detection of small nodules (1-5 mm) that are not usually visible on chest radiographs [9-11]. While the majority are most likely benign, recent studies of resected small nodules have shown that a considerable number are either primary or secondary pulmonary malignancies [12,13]. Consequently small nodule size does not exclude malignancy.

Typically, benign nodules have well-defined margins and a smooth contour while malignant nodules have poorly defined or spiculated margins and a lobular or irregular contour (Figs. 7,8, and 9) [7,14-17]. There is, however, considerable overlap between benign and malignant nodules in this regard. For instance, although a spiculated margin with distortion of adjacent vessels (often described as a sunburst or corona radiata appearance) is highly suggestive of malignancy, benign nodules can occasionally have this appearance.

Figure 6 Small nodule visualization using maximal intensity projection (MIP) image. (A) Computed tomography shows small nodular opacity in left lung (arrow). Confident differentiation from pulmonary vessels is difficult. (B) Axial MIP image allows nodule (arrow) to be more easily differentiated from tubular vessels.

Figure 6 Small nodule visualization using maximal intensity projection (MIP) image. (A) Computed tomography shows small nodular opacity in left lung (arrow). Confident differentiation from pulmonary vessels is difficult. (B) Axial MIP image allows nodule (arrow) to be more easily differentiated from tubular vessels.

Also, up to 20% of malignant nodules have smooth contours and well-defined margins [7,15]. These characteristics are more typically observed in metastatic lesions than in primary lung neoplasms.

Internal morphology of a nodule, with the exception of fat [attenuation of -40 to -120 Hounsfield units (HU)] and calcification, is unreliable in distinguishing a malignant from a benign nodule [7,14,15,18-20]. Fat within a nodule is a characteristic finding of hamartomas and is detected by CT in up to 50% of these neoplasms (Figs. 10 and 11) [19]. While this finding negates further evaluation, hamartomas constitute a very small percentage of SPNs. Calcification of a nodule can be useful in determining benignity, although the majority of benign nodules are not calcified [7,18]. Calcification that is diffusely solid, centrally punctate, laminated, or ''popcornlike'' in appearance is diagnostic of a benign nodule. Occasionally, however, benign-appearing calcification can be seen in metastatic nodules in patients with osteo-sarcoma (Fig. 12). Furthermore, calcification can be detected histopathologi-cally in up to 14% of lung cancers and is occasionally visible on CT [21,22] (Fig. 13). This calcification is typically stippled, eccentric, or amorphous. De-

Figure 7 Mucormycosis manifesting as solitary pulmonary nodule in a patient with multiple myeloma. (A) Chest radiograph shows well-circumscribed pulmonary nodule (arrow). (B) Computed tomography confirms left upper lobe pulmonary nodule. Note well-defined margins and smooth contour, findings suggestive of a benign etiology.

Figure 7 Mucormycosis manifesting as solitary pulmonary nodule in a patient with multiple myeloma. (A) Chest radiograph shows well-circumscribed pulmonary nodule (arrow). (B) Computed tomography confirms left upper lobe pulmonary nodule. Note well-defined margins and smooth contour, findings suggestive of a benign etiology.

tection of this pattern of calcification suggests a high probability of malignancy, although a similar pattern can occasionally be seen in benign nodules.

Computed tomography is a considerably more sensitive imaging modality for detecting calcification when compared to radiographic evaluation [14,20,23]. Calcification is usually detected visually when thinly collimated slices (1 to 3 mm) are performed through the nodule (Fig. 14). Partial volume

Figure 8 Solitary metastasis from renal cell malignancy. Computed tomography shows nodule (arrow) with lobular contour in right lower lobe. Lobular contour is due to uneven growth, a finding often associated with malignancy.
Figure 9 Non-small-cell lung cancer. Computed tomography shows nodule in right upper lobe with irregular contour and spiculated margin. Appearance is highly suggestive for malignancy.
Figure 10 Hamartoma. Computed tomography shows small, peripheral well-circumscribed nodule in right upper lobe (arrow). Low attenuation within nodule (attenuation — 106 HU) is consistent with fat and diagnostic of hamartoma.
Figure 11 Hamartoma. Computed tomography shows well-circumscribed nodule in right upper lobe. Focal punctate calcifications are suggestive of hamartoma. Similar calcifications can, however, be seen in carcinoid tumors. Small focal areas of fat within the nodule are diagnostic of hamartoma (arrow).

Figure 12 Metastatic osteosarcoma. (A) Computed tomography shows small, high attenuation nodule in lower lobe (arrow). The appearance is suggestive of a benign etiology. (B) Computed tomography obtained 3 months later reveals interval growth of nodule. Resection revealed metastatic osteosarcoma.

Figure 12 Metastatic osteosarcoma. (A) Computed tomography shows small, high attenuation nodule in lower lobe (arrow). The appearance is suggestive of a benign etiology. (B) Computed tomography obtained 3 months later reveals interval growth of nodule. Resection revealed metastatic osteosarcoma.

Figure 13 Non-small-cell lung cancer. Computed tomography reveals amorphous calcification in nodule, a pattern typical of malignancy (arrowheads). Adenocarcinoma was confirmed at resection.

Was this article helpful?

0 0
Stop Smoking, Kick The Habit Now

Stop Smoking, Kick The Habit Now

Now You Can Quit Smoking And Start Living a Healthy Life Yes, You! Have You Ever Thought There’s No Way You Can Give Up Cigarettes Without Losing Your Mind? Well, Worry No More.

Get My Free Ebook


Post a comment