Key points
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Benign cardiac masses are exceedingly rare, and the underlying pathophysiological mechanisms behind their emergence are poorly understood
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Most patients are asymptomatic unless the mass exerts an effect over cardiac mechanics, hemodynamics, or depolarization, or if cardioembolism results from the mass
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An understanding of the surgical features of cardiac masses is essential for the diagnosis and successful excision thereof ( Boxes 19.1 and 19.2 )
Box 19.1
Introduction
Cardiac tumors are rare and, when they occur, they are most frequently benign. The autopsy incidence of primary cardiac tumors ranges from 0.001% to 0.3%. Metastatic tumors, on the other hand, are the most common tumors of the heart with the reported ratio of cardiac metastases to primary cardiac tumors ranging from 100:1 to 1000:1. More than three-fourths of primary cardiac tumors are benign, with the cardiac myxoma representing the majority of these neoplasms. The most common cardiac tumor in children is the rhabdomyoma. This chapter details the surgical features, investigations, and manifestations associated with key examples of benign cardiac tumors.
Box 19.2
There are a range of known benign cardiac masses, the majority of which are benign tumors that are exceedingly rare in modern practice. Hence, an appreciation of their surgical features (namely, presentation, approach to imaging, visual appearance, and tissue characterization) is beneficial.
Entity
Description
Myxoma
Figs. 19.3–19.6
Overview
Cardiac myxomas are the most common form of cardiac tumors, though to account for up to 50% of all adult cardiac tumors. It affects primarily 40- to 60-year-olds and is associated with a female-male ratio of 3 . The majority of cases are thought to be sporadic. Though the underlying pathogenesis remains unclear, autosomal dominant transmission has been identified in familial atrial myxoma (less than 10% of cases) . Cardiac myxomas mostly arise from remnants of subendocardial or multipotent mesenchymal cells, around the fossa ovalis—75% of cases are attached to the left fossa ovalis .
Presentation
Though many patients with cardiac myxoma may be asymptomatic, some present with symptomatology and signs on examination consistent with mitral valve obstruction (e.g., syncope, dyspnea/orthopnea, and pulmonary congestion) and may exhibit embolic manifestations in later stages. Sudden death, weight loss, fatigue, pyrexia of unknown origin, and anemia have also been associated with cardiac myxoma .
Clinical examination of a patient with an indwelling cardiac myxoma should reveal :
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Tumor plop: a low-pitched diastolic sound produced by the tumor prolapsing into the left ventricle
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Systolic murmur (in 50% of cases), loud S1 (32% of cases), opening snap (26% of cases), or diastolic murmur (15% of cases)
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Peripheral stigmata of embolic phenomena, varying depending on the affected vasculature (neurological deficit, acute coronary syndrome, bowel or peripheral ischemia)
Investigations
Apart from the usual investigations undertaken when there is suspicion of cardiac pathologies (e.g., 12-lead ECG, routine bloods, troponin, etc.), the mainstay of diagnosis and detection of cardiac myxoma remains imaging and biopsy if needed. Transthoracic or transesophageal echocardiography (TTE and TEE, respectively) allows for the detection and localization of intracavitary masses, while further imaging techniques such as computed tomography (CT) or cardiac magnetic resonance (CMR) should be employed to discern and delineate the extent of the intracardiac mass, provide information on involvement of extracardiac structures, and provide information for preoperative planning . If imaging-based investigations are ambiguous, biopsy (guided by TEE) may be indicated to differentiate between tumors suitable for resection and metastatic tumors, as well as enabling histopathological analysis .
Differentials such as mitral stenosis, infective endocarditis, connective tissue disorders, and other cardiac tumors must be ruled out for a diagnosis of cardiac myxoma to be made.
Surgical Features
On visualization, cardiac myxomas typically are yellowish-brown and are frequently covered with thrombi. Size may vary from 1 cm to 15 cm, and 15–180 g . The surface of a cardiac myxoma is usually smooth, but cases in which myxoma have developed villous or papillary surfaces are also documented in literature. Unsurprisingly, spontaneous fragmentation of such papilla or villi poses increased embolic risk, and as such care should be taken during surgical resection .
Surgical resection of cardiac myxoma usually proceeds via the biatrial approach (under cardiopulmonary bypass and through median sternotomy) to afford the surgeon with optimal visualization and access to the lesion . The transseptal and unilateral left atrial approaches may also be taken. Once the myxoma stalk and underlying endocardium are resected, repair and closure of the excision site is required (as in up to 83% of cases) with autopericardium or prosthetic materials .
Lifelong follow-up is indicated as 5%–14% of cases are thought to feature recurrence; however, overall prognosis following successful tumor resection is good: 87% survival at 13 years. Tumors with irregular/friable surfaces are associated with increased risk of embolic complications .
Tissue Characterization
Myxomas are composed generally of myxoma cells—which arise from subendothelial vasoformative reserve cells and endothelial progenitors—as well as endothelial cells and smooth muscle fibers. Notably, the neoplastic cells are immunoreactive to S100, calretinin, vimentin, and nonspecific enolase .
Papillary fibroelastoma
Fig. 19.7
Overview
Cardiac papillary fibroelastoma (CPF) is the second most common type of benign cardiac tumor following cardiac myxoma . Similarly, the majority of patients with CPF are asymptomatic on presentation, however may present with manifestations secondary to cardioembolism (such as stroke, transient ischemic attack (TIA), myocardial infarct (MI), and angina) . CPF are usually found in the perivalvular area, arising from the papillary muscles. Unlike cardiac myxoma, CPF is slightly more common in men, who account for around 55% of CPF patients. The mainstay of treatment is successful surgical excision, and this is associated with excellent prognostic outlook .
Presentations
Clinical manifestations in patients symptomatic with CPF depend on the size, location, and extent of the tumor. Up to 30% of CPF are identified incidentally or on autopsy of patients without previous symptoms or findings suggestive of CPF . Overt clinical signs and symptoms in CPF are typically due to embolization of CPF fragments or associated thrombi, and therefore it is unsurprising that the most commonly associated clinical syndromes include stroke, TIA, syncope, angina, MI, and sudden cardiac death. Though the risk factors and underlying pathogenesis associated with CPF remain elusive, it is thought that CPF results from acquired rather than congenital processes, such as viral or traumatic causes .
Physical examination of a patient with CPF is unlikely to reveal any telltale signs; however, if cardioembolism secondary to CPF has occurred, stigmata of neurological, peripheral vascular, coronary, or mesenteric ischemia may result. It is likely that on investigation of the underlying cause of such manifestations CPF may then be identified and subsequently managed .
Investigations
Bearing in mind the rarity of CPF, and the fact that CPF patients may present with more “urgent” syndromes, it is more likely that CPF is uncovered incidentally during investigations during follow-up for, for example, a stroke or MI.
It is perhaps because of this paradox that echocardiography is the most commonly used imaging modality for the detection of CPF—not only is it widely indicated in patients presenting with such syndromes, but it also allows robust assessment of CPF location, attachment point, mobility, and morphology .
CPF tumors are, on average, 12.1 × 9.0 mm, but this ranges from 1 × 1 mm to 21 × 17 mm . Due to their relatively small size, initial identification on TTE should be followed up with TEE and specialist imaging modalities such as CMR . TTE for CPF, though perhaps useful as a first-line screening tool, is associated with suboptimal sensitivity as it fails to detect up to 38% of cases, while TEE on the other hand detects 15% more cases and misses only 23.4% thereof . On echocardiography, CPF appears with speckled echolucencies and simmers when intracardiac blood brushes against the tumor .
CT and CMR can subsequently characterize the tumor. On CMR, CPF is usually seen as a small, well-defined mobile nodule (notably the small size and mobility of CPF attenuates the efficacy of plain MRI in its diagnosis) and should appear similar in color to nearby myocardium on T1/T2-weighted imaging .
Surgical features
Successful surgical resection of CPF is usually curative as recurrence is rare. Tumors > 10 mm, overt symptoms, previous embolic events, and excessive tumor mobility are indications for open surgical excision. The role of anticoagulation in the management of CPF remains unclear .
The surgical appearance of CPF grossly features a centralized core with extensive radiating fronds, composed of a myxomatous core with elastic tissue .
Lipoma
Overview
Cardiac lipoma is a rare entity that mostly effects patients between the ages of 40 and 60 years old. It features proliferation of mature adipocytes, which then infiltrate into the myocardium and lead to downstream problems, for example refractory arrhythmias and sudden death . Approximately half of all cardiac lipoma cases are thought to originate from the subendocardium, while the remaining 50% are thought to arise from either the subepicardium or the myocardium itself. Cardiac lipomas are most often found in either the right atrium or left ventricle .
Presentation
The majority of patients with cardiac lipoma lack overt symptoms, therefore identification is usually incidental. Depending on the size and location of the neoplasm, cardiovascular symptoms such as chest tightness, dyspnea, or orthopnea may manifest, and ECG changes such as premature complexes, ventricular arrhythmias, or junctional rhythms may also be observed . On auscultation a tumor plop may be heard, similar to that which might be heard in cases of atrial myxoma.
Investigations
TTE remains the imaging modality of choice for invasive lipoma and can detect the size, shape, location, boundaries, and mobility of the tumor. In addition, the investigating physician should bear in mind the propensity for cardiac lipoma to cause associated aneurysmal dilation as well as its relationship with surrounding tissues. Hemodynamic changes resulting from cardiac lipoma may also be observed on TTE; however, TTE cannot conclusively differentiate between cardiac lipomas and other primary tumors such as LHIS .
TEE provides the clinician with enhanced view and should be done prior to intervention to confirm findings on TTE, and thereby further aid in surgical decision making.
CMR can be used to provide tissue characterization: increased T1-weighted signaling with septations within the mass should be observed .
Further, TEE may guide biopsy which will enable differentiation between cardiac lipoma, LHIS, and more importantly, to rule out well-differentiated liposarcoma. Finally, preoperative CT angio is useful to determine the relationship between the cardiac lipoma and coronary vasculature .
Histology
Histologically, cardiac lipomas are usually composed of mature adipocytes within a lipomatous capsule, with the absence of soft tissue components (which would suggest liposarcoma instead) and limited myocyte infiltration. Liposarcoma should also be ruled out by negative MDM2 gene amplification .
Lipomatous hypertrophy
Fig. 19.8
Overview
Lipomatous hypertrophy of the interventricular septum (LHIS) is an extremely rare entity, distinct from cardiac lipoma. There have hitherto been only a few case reports available in the literature. The disease process involves aberrant hypertrophy of adipocytes within the interventricular septum, without the presence of a lipomatous capsule, and with marked muscle fiber involvement. Notably, the majority of such cases are diagnosed at the postmortem stage .
Presentation
Similar to almost all other benign cardiac masses, patients with LHIS are often asymptomatic and detection is incidental at postmortem. Unlike intracavitary masses such as CPF, the intramural nature of LHIS means that the likelihood of cardioembolic events is low, and symptomatology associated with LHIS more likely involves insult to cardiac mechanics and conduction. Unsurprisingly therefore, the most common manifestations of LHIS include atrial fibrillation, premature complexes, supraventricular arrhythmias, junctional arrhythmias, or mild orthopnea. In the absence of such signs, the detection of LHIS is usually incidental .
Investigations
Initial investigations may reveal signs consistent with diminished cardiac output, in cases where LHIS has led to in/outflow obstruction or restricts myocardial contractility. The 12-lead ECG often reveals Wolff-Parkinson-White patterns, as well as the previously mentioned arrhythmias . This results from the neoplasm’s injurious effect on the cardiac conduction system. TTE may reveal a hyperechogenic mass within the interventricular septum, with or without outflow tract obstruction. Delineation of said mass is usually achieved via CMR, providing good imaging data on the degree of mixing between adipose and muscular tissue. LHIS appears as a hyperintense mass on T1-weighted CMR .
Prior to surgical intervention, CT angiography should be undertaken to establish the relationship between the mass and coronary blood supply, and biopsy should be considered if CMR is not able to distinguish between LHIS and cardiac lipoma. Finally, preoperative TEE should also be done to confirm the location and extent of the neoplasm, and the effect thereof on cardiac mechanics .
Surgical features
Following median sternotomy and establishment of CPB, open excision may proceed via right atriotomy followed by ventriculotomy. It is not uncommon for LHIS tumors to be removed piece by piece, depending on the degree to which the adipose tissue and muscle tissue intermix. Reconstruction of the septum and valve repair are also likely to be required. Notably, resection can be avoided in patients without symptoms, or with low risk of malignancy .
Tissue characterization
The cardinal features of LHIS that differentiate it from cardiac lipoma are the absence of a capsule, and tendency for there to be a mixture of brown and white adipose tissue within the neoplasm, intermixed with hypertrophied myocytes and fibrous tissues .
Rhabdomyoma
Figs. 19.9 and 19.10
Overview
Rhabdomyoma is considered the most common fetal cardiac tumor, accounting for up to 90% of tumors in the pediatric population . Rhabdomyoma, although extremely rare in the general population, is commonly found in those with the autosomal genetic condition tuberous sclerosis complex (TSC). Some studies have found that nearly 90% of children with TSC will have several rhabdomyomas . Rhabdomyomas are seen readily after 20 weeks of gestation and enlarge significantly during the second half of pregnancy . The majority of cardiac rhabdomyomas are asymptomatic and have a natural history of spontaneous regression. They are typically found in the ventricles, where they can compromise ventricular function and outflow . Due to asymptomatic nature and natural history of the condition, surgery is commonly reserved for symptomatic patients with significant hemodynamic obstruction .
Presentation
Rhabdomyomas are generally asymptomatic and therefore do not cause symptoms or hemodynamic compromise in the vast majority of patients . Clinical symptoms are largely related to the tumor size and location within the heart . Tumors of the ventricles can compromise ventricular function by obstructing inflow and outflow in addition to interfering with valvular function . Arrhythmias, common in patients suffering from TSC, may result from rhabdomyoma tumor tissue connecting atria to ventricle . Clinically, the presentation of arrhythmia in these patients can be extremely varied but may include fatigue, syncope (commonly confused with “drop seizures”), bradycardia, and palpitations .
Investigations
Prenatal ultrasound can be used as an important imaging modality. It can detect the presence of rhabdomyomas commonly after 20 weeks of gestation. Rhabdomyomas are thought to develop earlier than this; however, we are currently limited by the technical limits of ultrasonography . Echocardiography, however, is the imaging modality of choice for assessing cardiac involvement in TSC . It has high sensitivity with studies showing 75%–80% of rhabdomyomas satisfy criteria for TSC postnatally . Typically, rhabdomyomas are seen as multiple, echogenic, nodular masses which appear homogenous and hyperechoic compared with normal myocardium. Doppler echocardiography can also be used to assess the hemodynamic gradient across outflow tracts. This is an important tool for indicating surgery. MRI can also be used as an adjunct to echocardiography when and where the diagnosis of rhabdomyoma using echocardiography is unclear. Ultrasound is not commonly used; however if used, rhabdomyomas may be seen as solid hyperechoic masses .
Surgical features
Due to the natural history of spontaneous regression and asymptomatic nature of the tumor, surgical resection is not required in the vast majority of infants. Surgery is often reserved only for symptomatic patients with significant hemodynamic obstruction, with only a proportion of the 2%–5% of patients who present with heart failure requiring surgery . The goal of surgical excision is to provide immediate relief to acute outflow obstruction . Tumors are equally distributed between left, right, and septal myocardium . Surgical treatment for right ventricular outflow obstruction can be achieved via access through the tricuspid valve or via a right ventriculostomy if adequate resection through tricuspid valve is unattainable. Treatment of left ventricular outflow is more surgically challenging as the approach through aortic valve is limited by size of aortic annulus . Having said this, excellent short- and long-term results have been reported in multiple papers, suggesting the strength of surgical intervention .
Tissue characteristics
Macroscopically, rhabdomyomas are yellow-tan in color, solid, well circumscribed, and nonencapsulated lesions. These cells are derived from embryonal myoblast . Immunochemistry shows skeletal muscle differentiation with desmin and myoglobin and occasionally these cells may also express alpha smooth muscle actin or s100 receptor . Microscopically rhabdomyomas have a pathognomonic spider cell-like appearance with cytoplasmic strands of glycogen extending into the plasma membrane . Fetal rhabdomyomas show no obvious nuclear atypia and necrosis in contrast to adult rhabdomyomas .
Rhabdomyoma
Figs. 19.9 and 19.10
Overview
Fibroma is the second most common primary cardiac tumor in children, after rhabdomyomas . Fibroma is a fibroblast-rich tumor with intervening collagen and connective tissue, which is often extremely large in size. These tumors most commonly arise in the left ventricular free wall but they also can be found in the interventricular septum or right ventricular free wall . These tumors are rarely asymptomatic and do not regress spontaneously unlike rhabdomyomas.
Presentation
Patients can present asymptomatically or symptomatically. Common symptoms include dyspnea, syncope, fatigue, chest pain, angina, and palpitations .
On clinical examination, arrhythmias such as ventricular fibrillation and ventricular tachycardia are commonly observed in these patients . This is seen when the tumor involves the interventricular septum, inducing conduction defects . Cardiac fibromas are occasionally hemodynamically significant, obstructing ventricular inflow and outflow, resulting in valvular dysfunction, congestive heart failure, and sudden death. Heart murmurs are also commonly observed in this subgroup of patients . In contrast to myxoma and fibroelastoma, cardiac fibromas rarely cause embolic phenomena and rarely regress spontaneously unlike rhabdomyoma .
Investigations
TTE, CT, or MRI can be used as initial diagnostic modality depending on initial presentation as TTE (echocardiography) is a noninvasive, fast, and less expensive tool which is often used in the initial diagnosis of fibromas. In addition to providing information on tumor size, location, and surrounding structures, it can also provide information on ventricular and valvular function . MRI and CT help define tissue characteristic and extent of tissue involvement . On T1-weighted images the tumor appears isointense and hypointense (fibrous nature) on T2-weighted imaging, a distinct feature of fibroma, uncommon in other cardiac tumors . In CT imaging, cardiac fibromas appear as homogenous soft tissue masses, with calcification seen in approximately 25% of cases, another key finding which may further suggest fibroma . As a result of the avascular nature of the tumor, fibromas show late hyperenhancement, 7–10 min after administration of contrast, during perfusion imaging .
Surgical features
Fibromas are classically single tumors and range from 2 to 10 cm in size . Surgical resection is currently recommended in symptomatic fibromas; however, there is growing consensus that this should be extended to asymptomatic patients . Surgical resection is a curative treatment that has been shown to alleviate the need for defibrillator and long-term antiarrhythmic medications . Resection is associated with low operative morbidity and mortality and excellent mean survival . Median sternotomy using CPB with aortic cross clamping creates a bloodless operative field. An incision is then created on the ventricular wall, allowing access to the tumor. The borders of fibroma can be easily identified, allowing a plane to be readily developed by sharp dissection. After resection of the tumor, the defect can either be closed by primary repair (small defects) or by patch repair (suitable for larger defects). Patch repair prevents distortion of tissue and excessive reduction of ventricular cavity, which may cause heart failure .
Tissue characteristics
Fibromas are well defined, solitary, firm gray-white neoplasms that are often partially calcified and without a tumor. Microscopically, they feature collections of spindle-shaped fibroblasts interspersed with abundant collagen and elastic fibers. Fibromas have low cellularity and therefore have large extracellular spaces . Fibromas, unlike other primary cardiac tumors, have no foci of cystic change or necrosis with occasional aggregates of lymphocytes and sparse inflammation at the junction between tumors and uninvolved myocardium . These cells show myofibroblast differentiation and are positive for vimentin and smooth muscle actin. However, they are negative for CD34, S100, and HMB45 .
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