A Rare Case of Solitary Cardiac Myofibroma in an Infant

Introduction

Cardiac tumors are rare clinical conditions, with an incidence rate of 0.027% to 0.08%.^1,2 Among those, cardiac myofibroma is exceedingly rare. Here, we present an infant with solitary cardiac myofibroma in a challenging location where subtotal resection was performed and favorable short-term outcome was achieved. To our knowledge this is also the first case report that demonstrates magnetic resonance imaging (MRI) findings of this rare cardiac tumor.

Case Presentation

A previously healthy two-month-old female infant was found to have a new systolic murmur during a well-child visit. She was clinically asymptomatic and gaining weight well. There was no family history of cardiac disease or dysmorphic features. Her physical examination was normal other than a 2/6 high-pitched systolic murmur at the left lower sternal border and apex. There was no skin or subcutaneous lesions noted.

Transthoracic echocardiogram revealed a 2 cm × 1 cm mass originating from the anterolateral papillary muscle (Figure 1). Mitral valve diastolic mean gradient was 14 mm Hg (heart rate 153 bpm) in the setting of severe mitral valve regurgitation (Figure 1D). Estimated right ventricular systolic pressure was 55 mm Hg above the right atrial pressure. The left atrium was severely enlarged with normal left ventricular chamber size and biventricular function.

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Figure 1.

Preoperative echocardiography. (A) Parasternal long-axis view, (B) parasternal short-axis view, and (C) apical four-chamber view revealed a mass measuring about 2 cm × 1 cm. This mass originates from the anterolateral papillary muscle and extends through the central coaptation of the mitral valve. Severe mitral valve regurgitation was demonstrated in (D) the apical four-chamber view. Asterisk: left ventricular outflow tract, Red arrow: the mass, White arrowhead: mitral valve regurgitation. Abbreviations: LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle

Cardiac MRI showed homogeneity on T1-weighted images with a distinct border, hyperintensity on T2-weighted images, hypointensity on first-pass perfusion imaging, and no enhancement on delayed postcontrast imaging (Figure 2). No additional lesions or enlarged lymph nodes were found in the lungs or chest wall.

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Figure 2.

Preoperative cardiac magnetic resonance imaging. The mass was homogeneous on T1-weighted imaging (A), and hyperintense on T2-weighted imaging (B). It was hypointense of first-pass perfusion imaging (C) and showed no enhancement on delayed myocardial imaging (D). Red arrow: the mass. Abbreviations: LV, left ventricle; RV, right ventricle

Surgical excision of the tumor and mitral valve repair were performed due to severe mitral valve regurgitation and the risk of systemic emboli. On intraoperative examination, the mass arose from the head of the anterolateral papillary muscle and densely adhered to the posterior leaflet before extending as a pedunculated mass with a fibrous shell into the left atrium. Because complete resection of the mass was impossible given the critical valvar components involved, subtotal resection was performed, and the base of the resected area was treated with cryoablation (Figure 3A and B). The portion of the mitral valve in the A1/P1 region remained restricted from residual mass inferiorly and appeared to be the source of regurgitation. We obliterated the A1/P1 commissure to restore valve competence, while also not causing stenosis. This was done with leaflet-to-leaflet approximation and an eccentric annuloplasty.

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Figure 3.

Surgical findings and results. Gross appearance (A and B): A white, solitary mass measuring about 1.5 cm × 1 cm. Four-month postoperative echocardiogram (C and D): apical four-chamber view showing mean diastolic mitral valve gradient of 4 mm Hg at a heart rate of 122 bpm and trivial mitral valve regurgitation. MVΔP: mitral valve diastolic gradient. Abbreviations: LA, left atrium; LV, left ventricle

Pathological evaluation confirmed the mass as myofibroma (Figure 4). The postoperative course was uneventful, leading to discharge on postoperative day 7 with aspirin as the only medication. At the second follow-up four months postsurgery, the echocardiogram showed no evidence of recurrence, with trivial mitral valve regurgitation and a mean diastolic gradient of 4 mm Hg (Figure 3C and D).

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Figure 4.

Histopathologic features. (A) At low power, the lesion is variably cellular with mostly peripheral cellularity and bland central necrosis (likely autoinfarction). (B) At high power, the lesion consists of a bland spindle cell proliferation with a collagenous and focally myxoid stroma.

Discussion

Myofibromas are rare, mesenchymal tumors that have three described categories: solitary, multifocal without visceral involvement, and generalized with both cutaneous and visceral involvements. ³ The solitary form is the most common subtype, accounting for 50% to 85% of all cases. ³ It is commonly found on the skin or in the subcutaneous tissues of the head and neck. ⁴ The multifocal form involves skin, subcutaneous tissues, muscles, and bone. Both solitary and multifocal myofibromas are considered benign tumors with a favorable prognosis, ³ while the generalized myofibroma is associated with higher morbidity and mortality, necessitating chemotherapy. ⁵ The most common site of visceral involvement is the lung, followed by the gastrointestinal tract. ⁵

Solitary cardiac myofibroma was reported only twice before. The first case documented its presence in a two-month-old male with severe right ventricular outflow tract obstruction. ⁶ The second case involved tumors in the left atrium, which led to hemiplegia from systemic emboli in a 12-month-old female. ⁷ This case also revealed a potential autosomal dominant mode of inheritance, with the baby's father having a histologically proven neonatal history of myofibromatosis. ⁷

Although cardiac MRI was not able to make the diagnosis in this case, it is still a valuable tool in differentiating cardiac tumor noninvasively. ⁸ In her case, the MRI provided further information on potential metastasis as the management is different depending on the subtypes of myofibroma. We did not administer chemotherapy after subtotal resection given that solitary myofibroma is considered benign and local recurrence is rare. ³ After the second follow-up visits four months after the surgery, we spaced out the visit to six months as there was no evidence of recurrence and the valve function remained good. Given the location of the tumor, the mitral valve function is another important factor in her outcome regardless of tumor recurrence. In this unique scenario, the long-term follow-up plan will be adjusted based on the patient's future clinical course.

To summarize, we presented the case of a rare, solitary cardiac myofibroma with echocardiogram, cardiac MRI, and histologic findings. To our knowledge this is the first report of cardiac myofibroma involving the papillary muscle of the mitral valve wherein subtotal resection was performed to ensure good valve function. The location of the tumor added complexity to her management. Fortunately, the patient's straightforward recovery and favorable short-term outcome emphasize the potential for successful management of this uncommon, likely benign cardiac tumor.