Caseous calcification of the mitral annulus

Caseous calcification, liquefactive necrosis or ‘toothpaste tumor’ of the mitral annulus refers to a calcified cardiac mass and a rare variant of mitral annular calcification that is often misdiagnosed as a cardiac abscess or cardiac tumor.

Epidemiology

Caseous mitral annular calcification is rare and most commonly found in older patients >60years. It has been described in <1% of patients with mitral annular calcification that is in <0.1% of the population on echocardiography and seems to be more common in women ^1-5. On autopsy studies, it was found in approximately 2.7% of cases with mitral annular calcification ^1,4.

Risk factors

Conditions that account as predisposing factors for caseous mitral annular calcification include ¹:

• end-stage renal disease

Associations

Caseous mitral annular calcification has been associated with the following conditions ^1-3:

• hypertension

• hypercholesteremia

• atrial fibrillation

Diagnosis

The diagnosis is based on typical findings on cardiac imaging especially echocardiography and cardiac CT constitute complementary imaging modalities. In doubtful cases, cardiac MRI can add supplementary information and can aid in the differentiation of cardiac tumors ^1,2.

Clinical presentation

Clinical symptoms are unspecific. Palpitations, dyspnea and rarely syncope have been reported in patients with caseous mitral annular calcification ^1-3. Most frequently this condition is found incidentally on cardiac imaging ¹.

Complications

Complications of caseous calcification of the mitral annulus include ^1,2:

• mitral regurgitation

• mitral stenosis (rare)

• bradyarrhythmias or atrioventricular block

• systemic embolic events

Pathology

Caseous mitral annular calcification is characterized by liquefaction and caseation, with toothpaste-like caseous milky material enveloped by a calcified shell ¹.

Etiology

The exact etiology is unknown.

An altered calcium phosphate metabolism is assumed to have a role in pathogenesis.

Location

The ‘toothpaste tumor’ is found in a periannular region on the ventricular or atrial side of the mitral annulus usually adjacent to the posterior leaflet, often in the region of the P1 and P2 scallops ^1,2. Less frequently it involves the anterior annulus or other parts of the annulus ^1,5.

Microscopic appearance

The following histological features have been described in caseous calcification of the mitral annulus ^1,6,7:

• eosinophilic amorphous acellular material with myxoid areas and hyaline degeneration

• surrounding inflammatory infiltrate of macrophages and lymphocytes

• calcifications and zones of necrosis

Radiographic features

Plain radiograph

A chest x-ray might show a calcified mass in projection to the mitral valve.

Echocardiography

On echocardiography caseous calcification of the mitral annulus appears as a round or oval echogenic soft tissue mass with central echolucency in a periannular location ⁵, bulging either into the left atrial or left ventricular cavity ¹. Unlike in mitral annular calcification it the majority of cases lack acoustic shadowing ^1,5.

CT

On cardiac CT caseous calcification of the mitral annulus appears as an oval or round hyperdense peripherally calcified mass on non-contrast CT and variably hyperdense after contrast administration ⁵. It typically lacks contrast enhancement ^1,2,5.

MRI

MRI will show a hypointense sausage-like mass in a periannular location adjacent to the mitral annulus ^1,2.

Signal characteristics

• cine SSFP: low signal intensity

• T1: low to intermediate signal intensity

• T2/STIR: low signal intensity, hyperintense rim

• perfusion: no contrast enhancement

• IRGRE/PSIR: peripheral late gadolinium enhancement

Radiology report

The radiological include a description of the following:

• location and extent of the calcified mass with respect to the mitral valve

• mitral valve regurgitation

Treatment and prognosis

‘Toothpaste tumors’ of the mitral annulus are considered dynamic and rather benign conditions that can resolve spontaneously and transform back into normal mitral annular calcification and they can recur after surgical excision. They can cause complications and there is no clear consensus on the management ¹.

If they do not impede ventricular filling and are no source of significant other complications they can be treated medically. Surgical intervention should be considered in mitral valvular dysfunction or systemic embolic events or if other cardiac tumors cannot be excluded ^1,2 and in this case mitral valve replacement is preferred over mitral valve repair ¹.

History and etymology

A few cases of caseous calcification of the mitral annulus were already described by Ariela Pomerance in an autopsy series in 1970 ^1,4.

Differential diagnosis

Conditions that might mimic the imaging appearance of a ‘toothpaste tumor’ of the mitral annulus include ^1,2,5:

• mitral valve leaflet calcification

• mitral annular calcification (usually C-, U-, J- or O-shaped, acoustic shadowing)

• cardiac abscess (very similar appearance, lacks calcification, fluid-dense, peripheral)

• vegetations (mobile mass)

• intracardiac thrombus (avascular, non-calcified)

• cardiac tumors

  • myxoma (variable shape, no calcifications, highly vascular)

  • fibroelastoma (mobile mass)

  • angiosarcoma (infiltrative features, heterogeneous contrast enhancement)

  • cardiac metastases (contrast enhancement)