Caseous Calcification of the Mitral Annulus Mimicking an Intracardiac Cystic Tumor: A Report of Two Cases

Abbreviations

CCMA, Caseous calcification of the mitral annulus

CT, Computed tomography

MAC, Mitral annular calcification

INTRODUCTION

Caseous calcification of the mitral annulus (CCMA) is a rare variant of mitral annular calcification (MAC), with an estimated prevalence of approximately 0.07% in the general population and around 0.6% among patients with MAC.¹ It is most frequently observed in elderly individuals, females, and patients with end-stage renal disease undergoing hemodialysis. While calcification may occur in various locations of the mitral annulus, it most commonly involves the posterior leaflet.^2,3 The exact pathogenesis of CCMA remains unclear but is thought to be associated with disturbances in calcium metabolism⁴ and hypercholesterolemia. Common complications include mitral regurgitation, mitral stenosis, bradycardia, and systemic embolic events. Most patients are asymptomatic and can be managed conservatively with close follow-up. Interestingly, some case reports have described spontaneous resolution of CCMA.^5,6 Surgical intervention is generally reserved for cases with significant mitral valve dysfunction, embolic complications, or when the possibility of a cardiac tumor cannot be excluded. Mitral valve replacement is typically preferred over valve repair in these scenarios. In this report, we present two cases of CCMA and describe their shared imaging characteristics to raise awareness of this uncommon but clinically significant condition.

CASE REPORTS

Case 1

A 83-year-old female with a medical history of hypertension presented with progressive dyspnea that had been ongoing for several years. She had previously been diagnosed at another hospital with a mass located at the posterior mitral leaflet, accompanied by severe pulmonary hypertension. She was referred to our institution for further evaluation and surgical management. Transthoracic echocardiography revealed a 16.57 × 20.17 mm² mass attached to the posterior mitral valve, along with severe mitral regurgitation (Figure 1B). The contrast-enhanced computed tomography (CT) demonstrated a hypodense lesion with peripheral hyperdense calcification at the posterior mitral annulus (Hounsfield units central: 4-66, peripheral 107-316) (Figure 1A). Intraoperatively, we observed severe fibrotic thickening of the P1 and P2 segments of the posterior mitral leaflet, with a cystic-like appearance (Figure 1D). The posterior leaflet was excised and replaced with a bioprosthetic valve. Upon incision of the excised valve, a transparent fluid was released (Figure 1E). Pathological examination of mitral valve revealed calcification and degeneration changes (Figure 1C).

Figure 1.

In case 1 (A) Non-enhanced/contrast-enhanced computed tomography (CT) scan demonstrated a centrally hypodense mass with peripheral calcification. (B) Transthoracic echocardiography revealed a mass attached to the posterior mitral leaflet in long axis view. (C) Hematoxylin and eosin (H&E) staining revealed degenerative valvular tissue characterized by hyalinization and calcification. (D) Intraoperative view showing a partially calcified mass on the posterior mitral valve. (E) Transparent fluid was observed upon incision of the lesion.

Case 2

A 79-year-old female with a history of hypertension, end-stage renal disease on hemodialysis twice weekly, and a right-sided subdural hemorrhage four years ago, was admitted to our emergency department due to worsening dyspnea, productive cough, and poor appetite. A chest X-ray revealed increased bilateral lower lung infiltrates. Laboratory tests showed elevated C-reactive protein and white blood cell count, raising suspicion for pneumonia, and empiric antibiotic therapy with Imipenem/Cilastatin was initiated. Blood cultures returned negative. During her stay in the intensive care unit, the patient developed oxygen desaturation requiring intubation. A bedside echocardiogram revealed a mass on the posterior mitral valve, along with moderate to severe mitral regurgitation (Figure 2B). The contrast-enhanced CT performed five days later showed a hypodense mass with peripheral calcification on the posterior mitral annulus (Hounsfield units central: 54-82, peripheral 105-214), measuring approximately 27 × 28 mm² (Figure 2A). Surgical exploration revealed a caseous mass involving the posterior mitral valve (Figure 2D). On incision, thick whitish material was expressed from the lesion (Figure 2E). The affected posterior leaflet was resected and replaced with a porcine bioprosthetic valve. Histopathological analysis confirmed degenerative changes in the specimen (Figure 2C).

Figure 2.

In case 2 (A) Non-enhanced/contrast-enhanced computed tomography (CT) showed a mass with similar characteristics to case 1, exhibiting central hypodensity and peripheral calcification. (B) Transthoracic echocardiography revealed a large mass located on the posterior mitral valve leaflet on apical view. Another mass located in the left atrium was an artifact caused by the vertebral body. (C) Hematoxylin and eosin (H&E) staining demonstrated valvular tissue with fibrotic changes and calcification, consistent with degenerative pathology. (D) Intraoperative findings demonstrated a caseous mass on the posterior leaflet during mitral valve replacement. (E) A thick, milky-like fluid (arrow) was observed upon incision of the mass.

DISCUSSION

CCMA is an uncommon form of mitral annular calcification that can mimic other cardiac masses such as infective vegetations, tumors, or thrombi. However, several distinguishing features can aid in the differential diagnosis. Unlike tumors, CCMA typically presents as a cystic, calcified mass without internal vascularity on imaging studies. The absence of elevated inflammatory markers (e.g., C-reactive protein, white blood cell count) and negative blood cultures further reduce the likelihood of an infectious etiology. Although the pathology of CCMA remains unknown, it is believed to be associated with abnormal metabolic calcification and cholesterol. An analysis of the internal fluid material has identified the presence of calcium, fatty acids, cholesterol, and inflammatory cells.⁷ The clinical presentation of CCMA varies and largely depends on the size and location of the lesion. When the mass involves the mitral valve apparatus, valvular dysfunction such as regurgitation or stenosis may occur. Involvement of the interventricular septum may result in conduction abnormalities such as bradycardia or atrioventricular block.⁸ Embolic events can occur secondary to dislodgement of calcific material. Echocardiography remains the first-line diagnostic tool due to its accessibility and ability to identify the location and morphology of CCMA. Additional imaging modalities such as CT or cardiac magnetic resonance imaging can provide further detail and help exclude alternative diagnoses. Management depends on symptom severity and clinical complications. Asymptomatic patients may be managed conservatively with regular follow-up, and spontaneous resolution has been reported in rare cases. Surgical intervention is indicated in patients with significant mitral valve dysfunction, embolic complications, or when malignancy cannot be ruled out. Mitral valve replacement is generally preferred over repair due to the extensive calcification and structural damage often present. In our cases, both patients were elderly hypertensive females with similar symptoms and posterior mitral valve masses identified incidentally. One patient had normal renal func-tion, while the other had end-stage renal disease on hemodialysis — a known risk factor for CCMA. Both patients underwent mitral valve replacement for severe mitral valve regurgitation complicated by heart failure. Histopathological analysis with hematoxylin and eosin staining revealed degenerative changes in both mitral valve specimens.

LEARNING POINTS

1. CCMA is a rare condition but should be considered in differential diagnosis when a mass is detected on the posterior mitral annulus region.

2. The presence of hypodense material surrounded by calcification on CT is a distinguishing imaging feature suggestive of CCMA.