JSTR MEETING NOTES

Cystic Tumor of the Atrioventricular Node Computed Tomography and Magnetic Resonance Imaging Findings Kazuhiro Suzuki, MD, PhD,* Satoshi Matsushita, MD, PhD,w Hiromasa Suzuki, MD, PhD,z Kishio Kuroda, MD,w Hirotaka Inaba, MD, PhD,w Atsushi Arakawa, MD, PhD,y Takuo Hayashi, MD, PhD,y Atsushi Amano, MD, PhD,w and Ryohei Kuwatsuru, MD, PhD*

Key Words: cardiac tumor, cystic tumor of the atrioventricular node, computed tomography, magnetic resonance imaging

(J Thorac Imaging 2014;29:W97–W99)

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ystic tumor of the atrioventricular node (CTAVN) is a rare primary cardiac tumor and the smallest tumor capable of causing sudden death.1 Because most cases of CTAVN are diagnosed incidentally at autopsy, there are few published reports of CTAVN that have included imaging findings.2 We describe a case of CTAVN that was discovered in a living patient and successfully resected, including a description of the computed tomography (CT) and magnetic resonance imaging (MRI) findings.

CASE A 61-year-old woman with rheumatoid arthritis was referred to our institution for treatment of a cardiac tumor that was discovered incidentally on thoracic CT. She had no history of cardiac symptoms or arrhythmia. Echocardiography revealed a rounded echogenic mass in the right atrium. CT showed a 3 cm rounded mass in the medial portion of the right atrium. The lesion was of high attenuation on unenhanced CT (Fig. 1A). After contrast

medium had been administered, the lesion showed no contrast enhancement. The lesion’s attenuation appeared similar to the right atrium that was opacified with contrast medium, making it difficult to confirm on enhanced CT (Fig. 1B). On MRI, the lesion showed high signal intensity on black-blood T1-weighted images with fat suppression and low signal intensity on black-blood T2-weighted images with fat suppression (Fig. 2). Clinically, the differential diagnosis for a right atrial mass includes papillary fibroelastoma, myxoma, and hemangioma; however, the imaging findings were inconclusive in this case. The patient subsequently underwent surgery to resect the lesion. The right atrium was opened by means of a median sternotomy, and a 3 cm, yellowish, well-defined mass was found in the triangle of Koch. To examine the contents of the mass, fine-needle aspiration was attempted, but no material could be aspirated. The lesion was completely dissected from the wall of the right atrium and successfully removed. Microscopically, the lesion was a monolocular cyst lined by squamous epithelium with focally attached sebaceous glands. No papillary lesions extending into the duct lumen were observed. The lesion was diagnosed as CTAVN. The patient recovered uneventfully and 1 year after surgery had experienced no cardiac symptoms or arrhythmia (Fig. 3).

DISCUSSION To the best of our knowledge, only 8 cases of antemortem diagnosis of CTAVN have been published in the

FIGURE 1. Thoracic CT of CTAVN. Attenuation value of the lesion is 139 HU on unenhanced CT (A, arrow). On enhanced CT, the attenuation value of the lesion is 138 HU (B, arrowhead).

From the Departments of *Radiology; wCardiovascular Surgery; zCardiovascular Medicine; and yHuman Pathology, Faculty of Medicine, Juntendo University, Bunkyo-ku, Tokyo, Japan. The authors declare no conflicts of interest. Reprints: Kazuhiro Suzuki, MD, PhD, Department of Radiology, Faculty of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 1138421, Japan (e-mail: [email protected]). Copyright r 2014 by Lippincott Williams & Wilkins

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FIGURE 3. Microscopic findings (A, low-power view; B, highpower view). The lesion is lined by squamous epithelium with focally attached sebaceous glands.

FIGURE 2. Cardiac MRI images of CTAVN electrocardiogram (ECG)-gated black-blood T1-weighted turbo spin echo (TSE) image with a fat suppression prepulse [spectral presaturation inversion recovery (SPIR)] (TR: 666 ms, TE: 6 ms, FA: 90 degrees, slice thickness: 6 mm) reveals a high–signal intensity lesion (A, arrow). ECG-gated black-blood T2-weighted TSE image with a fat suppression prepulse (SPIR) (TR: 1333 ms, TE: 70 ms, FA: 90 degrees, slice thickness: 7 mm) reveals a low–signal intensity lesion (B, arrowhead). FA indicates flip angle; TE, echo time; TR, repetition time.

literature to date.1–3 Over 70 case reports of this rare cardiac tumor have been published in the literature; however, antemortem diagnosis is extremely rare, because the majority of CTAVN are discovered incidentally at autopsy. In previously published reports of antemortem diagnosis of CTAVN, most of the patients have had some degree of cardiac symptoms or arrhythmia. In contrast, the patient described in this report had no history of symptoms related to the lesion. In this case, the CTAVN was discovered incidentally on thoracic CT images. According to previously published reports, tumor size varies from 0.5 to 30 mm, and there is no relationship between tumor size and the occurrence of lethal arrhythmia.3 The cause of lethal arrhythmia in patients with CTAVN is still uncertain. Both the prognosis for CTAVN and the cause of lethal arrhythmia in patients with this condition remain uncertain because of the small number of cases reported. However,

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surgical resection might be a suitable treatment option to prevent sudden death caused by the lesion in cases of CTAVN diagnosed in living subjects. Because of the rareness of this tumor, few case reports have included imaging findings1,4,5; however, these reports do show that CTAVN appears as either a high-attenuation1 or low-attenuation4 lesion on CT images and as a high– signal intensity lesion both on T1-weighted1,5 and T2weighted MRI.1 The lesion in this patient had a highattenuation appearance on unenhanced CT, which is consistent with previous findings.1 However, on MRI, the lesion showed high signal intensity on T1-weighted images, which is consistent with previous findings,1,5 but showed low signal intensity on T2-weighted images, which is not consistent with previous findings.1 Histopathologically, CTAVN typically appears as a cyst-like structure or as an area of thickening with small, fluid-filled cysts in the atrioventricular nodal region. In previous case reports, the intracystic component has been described as a dark-green semisolid material,5 a gray caseating fluid,4 or a yellow caseous material1; however, no more detailed information was given in these reports. Therefore, it is possible that the attenuation seen on CT and the signal intensity seen on MRI vary according to the composition of the intracystic component. We speculate that the lesion described in this report was composed of calcification or protein-rich fluid such as keratinous debris on the basis of attenuation on CT and signal intensity on MRI. CT showed no contrast enhancement in the lesion, which explains its cystic nature. The CT attenuation value of the lesion on unenhanced CT, which was r

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>100 HU, is a very high value for typical hemorrhage. Echocardiography findings might be feasible for protein-rich fluid; however, its composition was not confirmed because a specimen could not be collected by means of fine-needle aspiration. By definition, CTAVN occurs adjacent to the atrioventricular node, and similar lesions have not been described elsewhere in the body to our knowledge. CTAVN is thought to be of embryologic origin and is therefore not a true neoplasm because of its benign histologic appearance and invariable location in the atrioventricular area. The atrioventricular nodal region is an area of embryologic fusion, suggesting that either mesothelium or nearby foregut inclusion may be incorporated.3 It is important, therefore, to note that CTAVN should be diagnosed by its characteristic location in addition to its cystic nature, although the attenuation on CT and signal intensity on MRI may vary according to the composition of the intracystic component. In conclusion, we have described a rare case of CTAVN that was diagnosed antemortem. The tumor was

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CTAVN: CT and MRI Findings

successfully resected, and the location was characteristic for CTAVN. Radiologists should be aware that CTAVN is a life-threatening lesion that may be found incidentally on thoracic CT or MRI.

REFERENCES 1. Saito S, Kobayashi J, Tagusari O, et al. Successful excision of a cystic tumor of the atrioventricular nodal region. Circ J. 2005; 69:1293–1294. 2. Law KB, Feng T, Nair V, et al. Cystic tumor of the atrioventricular node: rare antemortem diagnosis. Cardiovasc Pathol. 2012;21:120–127. 3. Guo J, Zuo S, Lin C, et al. Surgical treatment of a giant cystic tumor of the atrioventricular nodal region. Interact Cardiovasc Thorac Surg. 2009;8:592–593. 4. Kaminishi Y, Watanabe Y, Nakata H, et al. Cystic tumor of the atrioventricular nodal region. Jpn J Thorac Cardiovasc Surg. 2002;50:37–39. 5. Paniagua JR, Sadaba JR, Davidson LA, et al. Cystic tumour of the atrioventricular nodal region: report of a case successfully treated with surgery. Heart. 2000;83:E6.

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Cystic tumor of the atrioventricular node: computed tomography and magnetic resonance imaging findings.

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