Cystic Tumor of the Atrioventricular Node

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mandana Chitsazan, M.D. [2]

Synonyms and keywords:

Historical Perspective

Cystic tumor of the atrioventricular (AV) node was first reported by Armstrong and Mönckeberg in 1911.

Classification

There is no established system for the staging of the cystic tumor of the AV node.

Pathophysiology

The cystic tumor of the AV node is a benign congenital tumor. Although it is also called mesothelioma of the AV node, it appears to be a misnomer. The origin of the cystic tumor of the AV node is still controversial. It is believed that it has endodermal origin, derived from congenital rests during embryogenesis. One study suggested that cystic tumor of the AV node and solid cell nests of the thyroid have similar structures and may share the same developmental process; therefore it is assumed that cystic tumor of the AV node is an ultimobrachial heterotopia.

On gross pathology, small multiocular cysts are characteristic findings of the cystic tumor of the AV node. The tumor may be invisible from the endocardial surface of the heart. Therefore, sectioning through the infero-medial tricuspid annulus might be required.

On microscopic histopathological analysis, solid cell nests and cystic structures lined by flattened cuboidal or squamous epithelium mixed with rare neuroendocrine cells (C cells) are characteristic findings of the cystic tumor of the AV node.

On immunohistochemical staining, the main tumor cells stain positive for:

• Cytokeratin CAM5.2
• Cytokeratin AE1/AE3
• Cytokeratin 34βE12
• Cytokeratin 5/6 (CK5/6)
• Cytokeratin 7 (CK7)
• Eithelial membrane antigen (EMA)
• Carcinoembryonic antigen (CEA)
• Carbohydrate antigen (CA)19.9
• p63
• bcl2
• galectin 3

The neuroendocrine cells of the lesion stain positive for:

• CAM5.2
• Pan-keratin (AE1/AE3)
• CEA
• Calcitonin
• Chromogranin
• Synaptophysin
• hyroid Transcription Factor 1 (TTF1)

The tumor stains negative for:

• Keratin 20 (CK20)
• p53
• Bcl-2
• Cyclin D1
• Cytokeratin 20 (CK20)
• Vimentin
• CD31
• Factor VIII related antigen
• Estrogen receptor
• Progesterone receptor
• Thrombomodulin
• Wilm’s tumor 1
• Calretinin

However, true mesothelium stains positive for thrombomodulin, Wilm’s tumor 1, calretinin and negative for PAS. Fletcher, Christopher (2013). Diagnostic histopathology of tumors. Philadelphia, PA: Saunders/Elsevier. ISBN 9781437715347. The immunohistochemistry staining of the cystic tumor of the AV node is in favor of the epithelial differentiation of the tumor and supports the labeling of this tumor as an endodermal heterotopia.

Causes

The cause of the cystic tumor of the AV node has not been identified. Other midline developmental defects are seen in 10% of the patients. It suggests that a genetic defect might involve migration of embryological tissues and cardiac neural crest cell development with possible familial predisposition. Considering the absence of mitoses in the tumor, it is suggested to be resulted from a dilatation of cystic spaces rather than true neoplasm.

Differentiating Cystic Tumor of the AV node from Other Diseases

[Disease name] must be differentiated from other diseases that cause [clinical feature 1], [clinical feature 2], and [clinical feature 3], such as [differential dx1], [differential dx2], and [differential dx3].

OR

[Disease name] must be differentiated from [[differential dx1], [differential dx2], and [differential dx3].

Epidemiology and Demographics

The incidence/prevalence of [disease name] is approximately [number range] per 100,000 individuals worldwide.

There is no racial or ethnic predilection to the cystic tumor of the AV node.

Women are more commonly affected by the cystic tumor of the AV node than men. The female to male ratio is approximately 3 to 1.

The cystic tumor of the AV node is usually diagnosed in the fourth decade of life.

Risk Factors

There are no established risk factors for the cystic tumor of the AV node.

Screening

There is insufficient evidence to recommend routine screening for the cystic tumor of the AV node.

Natural History, Complications, and Prognosis

If left untreated, [#]% of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].

OR

Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].

OR

Prognosis is generally excellent/good/poor, and the 1/5/10-year mortality/survival rate of patients with [disease name] is approximately [#]%.

Diagnosis

Diagnostic Study of Choice

The diagnosis of [disease name] is made when at least [number] of the following [number] diagnostic criteria are met: [criterion 1], [criterion 2], [criterion 3], and [criterion 4].

OR

The diagnosis of [disease name] is based on the [criteria name] criteria, which include [criterion 1], [criterion 2], and [criterion 3].

OR

The diagnosis of [disease name] is based on the [definition name] definition, which includes [criterion 1], [criterion 2], and [criterion 3].

OR

There are no established criteria for the diagnosis of [disease name].

History and Symptoms

The majority of patients with [disease name] are asymptomatic.

OR

The hallmark of [disease name] is [finding]. A positive history of [finding 1] and [finding 2] is suggestive of [disease name]. The most common symptoms of [disease name] include [symptom 1], [symptom 2], and [symptom 3]. Common symptoms of [disease] include [symptom 1], [symptom 2], and [symptom 3]. Less common symptoms of [disease name] include [symptom 1], [symptom 2], and [symptom 3].

Physical Examination

Patients with [disease name] usually appear [general appearance]. Physical examination of patients with [disease name] is usually remarkable for [finding 1], [finding 2], and [finding 3].

OR

Common physical examination findings of [disease name] include [finding 1], [finding 2], and [finding 3].

OR

The presence of [finding(s)] on physical examination is diagnostic of [disease name].

OR

The presence of [finding(s)] on physical examination is highly suggestive of [disease name].

Laboratory Findings

An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].

OR

Laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].

OR

[Test] is usually normal among patients with [disease name].

OR

Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].

OR

There are no diagnostic laboratory findings associated with [disease name].

Electrocardiogram

There are no ECG findings associated with [disease name].

OR

An ECG may be helpful in the diagnosis of [disease name]. Findings on an ECG suggestive of/diagnostic of [disease name] include [finding 1], [finding 2], and [finding 3].

X-ray

There are no x-ray findings associated with [disease name].

OR

An x-ray may be helpful in the diagnosis of [disease name]. Findings on an x-ray suggestive of/diagnostic of [disease name] include [finding 1], [finding 2], and [finding 3].

OR

There are no x-ray findings associated with [disease name]. However, an x-ray may be helpful in the diagnosis of complications of [disease name], which include [complication 1], [complication 2], and [complication 3].

Echocardiography or Ultrasound

There are no echocardiography/ultrasound findings associated with [disease name].

OR

Echocardiography/ultrasound may be helpful in the diagnosis of [disease name]. Findings on an echocardiography/ultrasound suggestive of/diagnostic of [disease name] include [finding 1], [finding 2], and [finding 3].

OR

There are no echocardiography/ultrasound findings associated with [disease name]. However, an echocardiography/ultrasound may be helpful in the diagnosis of complications of [disease name], which include [complication 1], [complication 2], and [complication 3].

CT scan

Only a few cases of cystic tumor of the AV node have been reported antemortem. Therefore, the data regarding the imaging findings are limited. Reports have shown either a high-attenuation or low-attenuation lesions on CT images.

MRI

Cardiac MRI may be helpful in the diagnosis of the cystic tumor of the AV node. High-signal intensity lesion on T1-weighted and T2-weighted MRI or low signal intensity on T2-weighted MRI have been reported.

Other Imaging Findings

There are no other imaging findings associated with [disease name].

OR

[Imaging modality] may be helpful in the diagnosis of [disease name]. Findings on an [imaging modality] suggestive of/diagnostic of [disease name] include [finding 1], [finding 2], and [finding 3].

Other Diagnostic Studies

There are no other diagnostic studies associated with [disease name].

OR

[Diagnostic study] may be helpful in the diagnosis of [disease name]. Findings suggestive of/diagnostic of [disease name] include [finding 1], [finding 2], and [finding 3].

OR

Other diagnostic studies for [disease name] include [diagnostic study 1], which demonstrates [finding 1], [finding 2], and [finding 3], and [diagnostic study 2], which demonstrates [finding 1], [finding 2], and [finding 3].

Treatment

Medical Therapy

There is no medical treatment for the cystic tumor of the AV node.

Surgery

Because of the critical location of the tumor and its unfavorable prognosis, surgical excision is the mainstay of treatment for cystic tumor of the atrioventricular node. Anti-arrhythmic drugs and lifelong pacemaker placement may be necessary after excision to manage any post-surgical AV block.

Primary Prevention

There are no established measures for the primary prevention of the cystic tumor of the AV node.

Secondary Prevention

There are no established measures for the secondary prevention of the cystic tumor of the AV node.

References

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