MRI Web Clinic — October 2005

Incidental Findings on Musculoskeletal MR
Stephen F. Quinn, M.D.

Clinical History: A 58 year-old female presents with low back pain and is referred for a lumbar spine MR examination. (1a) T1- and (1b) T2-weighted axial images are provided. What are the findings? What is your diagnosis?

1a
1b
Figure 1:

(1a) T1- and (1b) T2-weighted axial images

Findings

2a
2b
Figure 2:

(2a) The T1-weighted image demonstrates a large heterogeneous mass involving the left kidney (arrows. (2b) The T2-weighted image confirms that the renal lesion is not a cyst, but rather a complex solid mass (arrows).

Diagnosis

Renal cell carcinoma.

Discussion

The incidental findings in spine and joint MR imaging will vary in type and frequency with the body part being imaged. Lumbar spine MR imaging is more likely to detect incidental findings than other examinations because of the higher number of organs and vessels in the field of view. Lumbar spine MR imaging may detect abnormalities of the kidneys, adrenal glands, liver, spleen, aorta and para-aortic regions, inferior vena cava, or the uterus and adnexal regions. No studies have been performed to evaluate the frequency of incidental lesions with spine and joint MR imaging, but the types of incidental findings with lumbar spine MR imaging are similar to those seen with CT colonography. In one analysis of 3488 patients undergoing CT colonography,1 40% of the patients had incidental findings, 14% had additional investigations and 0.8% were given immediate treatment. Extracolonic cancers were detected in 2.7% and 0.9% had an abdominal aortic aneurysm (AAA). Additionally, some patients had more than one significant incidental finding. The paradox of spine and joint MR imaging is that incidental findings are not uncommonly more significant than the musculoskeletal problems being evaluated.

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Figure 3:

(3a) This examination was obtained in a patient with back pain not relieved with conservative therapy. The T1-weighted sagittal image shows a large abdominal aortic aneurysm (AAA) (black arrows) with evidence of a rupture (white arrows).

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Figure 4:

(4a) Same patient as Fig. 3a. The axial T2-weighted image redemonstrates the AAA with a contained rupture (arrows) that extends into the right psoas muscle.

Many incidental lesions on MR are difficult to detect and characterize because the findings may only visible on scout images or are obscured by saturation bands. Scout images are obtained so that the MR technologist can plot out the locations for diagnostic MR images. Pulse sequences utilized for scout series are typically rapidly obtained and of low resolution, and as a result are suboptimal for characterizing lesions and the lesions are often incompletely visualized. Saturation bands are commonly used in spine imaging to suppress motion artifact from areas anterior to the spine. These saturation bands obscure anatomic detail, making detection of abnormalities anterior to the spine more difficult. Even when the lesions are detected, further imaging with MR, CT or ultrasound may be necessary to fully evaluate an abnormality. For example, uterine enlargement may be detected during lumbar spine or pelvic region imaging, but the images may be inadequate for characterization of the uterine enlargement, and thus further diagnostic evaluation becomes necessary.

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Figure 5:

(5a) This sagittal T1-weighted image shows an AAA (dotted lines) that is partially obscured by a saturation band (white arrows). AAA can be difficult to visualize when the examination is designed to evaluate the lumbar spine.

 

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Figure 6:

(6a) In this patient, the AAA (large arrows) was only visualized on the scout images. This aneurysm is saccular in morphology and arises from the anterior wall of the aorta. The AAA was not seen on the diagnostic images of the spine. Additionally, a nodal mass is present at the level of the aortic bifurcation (small arrows).

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Figure 7:

(7a) A sagittal T1-weighted image shows an AAA (white arrows), and also reveals multiple osseous lesions from unsuspected metastatic disease (asterisks).

 

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Figure 8:

(8a) The sagittal scout image demonstrates non-specific enlargement of the uterus. Usually uterine enlargement is due to benign fibroid disease, but this needs to be confirmed clinically or with additional imaging.

 

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Figure 9:

(9a) This coronal T2-weighted fat suppression image shows uterine enlargement due to multiple intramural and submucosal nodules (arrows). The nodules have characteristics typical of uterine fibroids.

The majority of the incidental MR findings involving solid organs are cysts. Cysts are commonly seen in the kidneys, liver, pancreas, adnexae and thyroid. It is important for the imager to differentiate simple cysts from other processes that need further evaluation. Although most incidental lesions of the kidneys are cysts, some will represent renal malignancies. For example, in an evaluation of 257 renal malignancies,2 93 (36.2%) were discovered incidentally with imaging studies. Solid and complex cystic processes will be detected,3-6 and such lesions require further evaluation. Additionally, important non-neoplastic abnormalities can be detected with MR imaging, including ureteral obstruction and reflux, diverticular disease and congenital anomalies.

 

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Figure 10:

(10a) The scout coronal plane image shows a complex left adnexal mass in a post menopausal woman (arrows). This type of lesion could represent a malignancy of arising from the left ovary, and warrants further evaluation.

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Figure 11:

(11a) This coronal scout image from a lumbar MRI reveals a dilated left renal collecting system and marked thinning of the renal cortex (arrows).

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Figure 12:

(12a) Same patient as Fig. 11. An additional coronal scout image shows a portion of the dilated renal pelvis and a dilated distal left ureter (arrows), consistent with chronic ureteral reflux.

It is important for the imager to decide which incidental findings need further evaluation. In one study looking at 231 patients who had cervical imaging with CT or MR,3 16% (36/231) had incidental thyroid lesions. Six of these patients had further workup with the cost of each workup being $1158. This example underscores the importance of differentiating benign from malignant solid processes when possible. For example, most adrenal lesions are incidental non-functioning adenomas, but some of these lesions are more significant. In a series of 40 incidental adrenal tumors,7 only one was found to be an angiosarcoma. An experienced imager can usually differentiate a benign adrenal adenoma from a malignant adrenal tumor based on its MR signal intensity characteristics.

In the evaluation of the thoracic spine, the most common incidental findings involve the thoracic aorta, paravertebral soft tissues, lung parenchyma, pleura and the mediastinum. In the cervical region, the most common incidental findings involve the thyroid, skull base, and nasopharynx. MR imaging of the joints detects fewer incidental findings than spine imaging. In the shoulder, abnormalities of the lung, pleura and chest wall are the most common incidental findings. In the knee, incidental findings include vascular abnormalities such as popliteal artery aneurysms and popliteal artery entrapment.

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Figure 13:

(13a) A sagittal T1-weighted image of the knee reveals an unsuspected popliteal artery aneurysm with mural thrombus (arrows). This diagnosis is important to make because of the propensity of such aneurysms to embolize and thrombose.

 

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Figure 14:

(14a) A coronal T1-weighted image from a shoulder MR examination shows a left perihilar tumor with extension to the lateral pleural margin (arrows). This represents an unsuspected lung cancer.

 

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Figure 15:

(15a) This axial T2-weighted image was part of a cervical spine MRI examination. An unsuspected solid nodule (arrow) is present in the left lobe of the thyroid gland. Although this will likely be a benign lesion, a solid nodule of this size requires further diagnostic evaluation.

As discussed above, missing or inadequately evaluating incidental lesions can impact negatively on the patient’s care. Additionally, such errors put the imager at risk for malpractice judgments. In a study of 18,860 malpractice lawsuits,8 47% of the radiology lawsuits related to missed diagnoses. Additionally, lawsuits alleging failure to order a radiologic examination have grown from 20% to 30% in the last 20 years.

Conclusion

Incidental findings seen on spine and joint MR imaging often change the management of patients. Incidental findings are often more significant than the musculoskeletal problems being evaluated. The imager needs to detect these incidental findings, characterize the lesions when possible, and recommend additional investigations appropriately.

References

1 Xiong T, Richardson M, Woodroffe R, Halligan S, Morton D, Lilford RJ. Incidental lesions found on CT colonography: their nature and frequency. Br J Radiol 2005; 78:22-29.

2 Leslie JA, Prihoda T, Thompson IM. Serendipitous renal cell carcinoma in the post-CT era: continued evidence in improved outcomes. Urol Oncol 2003; 21:39-44.

3 Yousem DM, Huang T, Loevner LA, Langlotz CP. Clinical and economic impact of incidental thyroid lesions found with CT and MR. AJNR Am J Neuroradiol 1997; 18:1423-1428.

4 Yang G, Chen Z, Peng Y, Liu W, Tao L. [Incidental renal cell carcinoma: analysis of 109 cases]. Zhonghua Wai Ke Za Zhi 2002; 40:445-447.

5 Slanetz PJ, Hahn PF, Hall DA, Mueller PR. The frequency and significance of adnexal lesions incidentally revealed by CT. AJR Am J Roentgenol 1997; 168:647-650.

6 Gorin AD, Sackier JM. Incidental detection of cystic neoplasms of the pancreas. Md Med J 1997; 46:79-82.

7 Pasqual E, Bacchetti S, Waclaw B, Bertolissi F, Grimaldi F, Cagol PP. Adrenal incidentalomas: indications for surgery. Chir Ital 2003; 55:29-34.

8 Berlin L, Berlin JW. Malpractice and radiologists in Cook County, IL: trends in 20 years of litigation. AJR Am J Roentgenol 1995; 165:781-788.

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