DOI:10.2214/AJR.05.0738
AJR 2007; 188:S5-S6
© American Roentgen Ray Society
AJR Teaching File: Solitary Pulmonary Nodule with Enhancing Rim Sign
John R. Muhm1 and
Catherine C. Roberts
1 Both authors: Department of Radiology, Mayo Clinic College of Medicine, 13400
E Shea Blvd., Scottsdale, AZ 85259.
Received April 30, 2005;
revised August 18, 2005;
Address correspondence to C. C. Roberts
(roberts.catherine{at}mayo.edu).
Keywords: chest • CT • lung • solitary pulmonary nodules
Clinical History
An 84-year-old man presents with a recent cough but does not have fever or
chills. On chest radiography, a solitary pulmonary nodule is identified.
Because previous chest radiographs are not available for comparison, the
lesion is studied with CT.
Radiologic Description
An axial CT image through a solitary pulmonary nodule acquired before the
administration of IV contrast material
(Fig. 1A) shows homogeneous
soft-tissue density. After administration of IV contrast material
(Fig. 1B), the nodule rim
enhances more intensely than the central portion. The center of the nodule
enhanced 17 H.
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Fig. 1A —84-year-old man with recent cough. (Reprinted with permission from
Muhm JR, McCullough AE. The enhancing rim: a new sign of a benign pulmonary
nodule. Mayo Clin Proc 2003; 78:1092-1096
[5]) Unenhanced CT scan through
solitary pulmonary nodule shows homogeneous rounded soft-tissue mass.
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Fig. 1B —84-year-old man with recent cough. (Reprinted with permission from
Muhm JR, McCullough AE. The enhancing rim: a new sign of a benign pulmonary
nodule. Mayo Clin Proc 2003; 78:1092-1096
[5]) After administration of IV
contrast material, nodule rim enhances more intensely than lower density
central portion. Center of nodule (region of interest marked) enhanced 17
H.
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Differential Diagnosis
The differential diagnosis includes granuloma, metastasis, bronchogenic
carcinoma, and round atelectasis.
Diagnosis
The diagnosis in this patient is benign granuloma.
Commentary
Solitary pulmonary nodules are commonly encountered in clinical practice.
Distinguishing benign from malignant processes with imaging can be a
challenge. Contrast-enhanced CT can help characterize solitary pulmonary
nodules
[1-3].
After the IV administration of iodinated contrast material, enhancement of 15
H or less is a strong predictor of benignancy
[4]. In a study of 111 nodules
that enhanced 15 H or less, 107 (96%) were benign. Of the 245 nodules that
enhanced more than 15 H, 167 (68%) were malignant
[4].
Using the technique described by Swensen et al.
[1], a new finding has been
observed in some benign solitary pulmonary nodules. This has been termed the
"enhancing rim sign" because it refers to a rim of enhancing soft
tissue at the periphery of a solitary pulmonary nodule that surrounds a
homogeneous lower density central portion of the nodule
[5]. This sign has been seen in
16 cases of benign nodules and in no cases of malignant nodules. Some of the
benign nodules that exhibited this sign had central portions that enhanced
more than 15 H. Pathologically, the enhancing rim sign corresponds to an
enhancing rim of fibrotic inflammatory tissue surrounding a necrotic center,
which in this case was caused by a necrotizing infection.
With respect to the other items in the differential diagnosis, bronchogenic
carcinoma and metastases that measure 3 cm or less in diameter usually show
homogeneous enhancement. Malignancies larger than 3 cm may have inhomogeneous
enhancement because of necrosis. The key differentiating factor is that the
necrotic central area will not be homogeneous. The enhancing rim sign has not
been seen in malignant pulmonary nodules. Round atelectasis will show
prominent homogeneous enhancement of the atelectatic lung. Round atelectasis
would not be expected to have a low-density center.
When an enhancing rim is seen surrounding a homogeneous lower density
center on contrast-enhanced CT, a benign process should be considered, even if
the central enhancement is greater than 15 H. Other features favoring a benign
process include a round to oval shape and a smooth margin. Necrotizing
granulomas can produce false-positive results on 18F-FDG PET
[6], complicating nodule
evaluation in regions endemic for granulomatous disease. If a nodule shows the
enhancing rim sign but also has another indeterminant sign, such as
enhancement greater than 15 H or spiculated borders, then CT should be
repeated in 3-4 months instead of sending the patient immediately to PET,
biopsy, or surgical resection.
Objective
The educational objective of this article is to review features
differentiating benign from malignant solitary pulmonary nodules on CT.
Conclusion
An enhancing rim sign can be helpful in differentiating benign from
malignant pulmonary nodules. CT follow-up remains necessary. This sign can be
especially helpful in regions endemic for granulomatous disease because
necrotizing granulomas can produce false-positive results on PET.
References
- Swensen SJ, Brown LR, Colby TV, et al. Pulmonary nodules: CT
evaluation of enhancement with iodinated contrast material.
Radiology 1995;194
: 393-398[Abstract/Free Full Text]
- Yamashita K, Matsunobe S, Tsuda T, et al. Solitary pulmonary
nodule: preliminary study of evaluation with incremental dynamic CT.
Radiology 1995;194
: 399-405[Abstract/Free Full Text]
- Swensen SJ, Brown LR, Colby TV, et al. Lung nodule enhancement at
CT: prospective findings. Radiology 1996;201
: 447-455[Abstract/Free Full Text]
- Swensen SJ, Viggiano RW, Midthun DE, et al. Lung nodule enhancement
at CT: multicenter study. Radiology 2000;214
: 73-80[Abstract/Free Full Text]
- Muhm JR, McCullough AE. The enhancing rim: a new sign of a benign
pulmonary nodule. Mayo Clin Proc 2003;78
: 1092-1096[Medline]
- Knight SB, Delbeke D, Stewart JR, Sandler MP. Evaluation of
pulmonary lesions with FDG-PET: comparison of findings in patients with and
without a history of prior malignancy. Chest1996; 109:982
-988
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Clinical History
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