Periannular Mitral Valve Prosthesis Crypts Mimicking Periprosthetic Abscesses

Abstract

Mitral annular abscesses are rare and can be caused by infective endocarditis. We present the case of a patient with an infected mitral prosthesis, with multiple suspected periprosthetic abscesses. However, perioperative inspection showed a supra-annular implanted prosthesis.

Graphical Abstract

History of Presentation

A 65-year-old man who underwent mechanical mitral valve replacement (MVR) 8 years earlier as a result of viridans group Streptococcus endocarditis was admitted with suspected recurrence of infective endocarditis (IE). Before the admission, the patient had 2 events of ischemic stroke. The first stroke occurred 6 months previously, and transthoracic echocardiography (TTE) showed normal function of the mitral valve without thrombus, low gradient over the prosthesis, and no signs of infections (no fever, normal leukocyte count, and low C-reactive protein [CRP]). Days before his presentation, the international normalized ratio (INR) was below target value and was already strongly fluctuating over a longer period of time. Therefore, the first stroke was interpreted to be caused by the relatively low INR, and acenocoumarol was switched to fenprocoumon.

Learning Objectives

• •To recognize the imaging characteristics of supra-annular implanted MVR.
• •To distinguish supra-annular implanted MVR from IE with paravalvular extension.

The second stroke occurred 3 weeks before admission. The INR had been stable in the therapeutic range (2.5-3.5) for months since the switch to fenprocoumon. Again, TTE showed good function of the mechanical prosthesis, with low gradient and without signs of thrombus. The CRP was slightly elevated at that time (17 mg/L). Transesophageal echocardiography (TEE) was performed and showed mobile masses (maximum length, 17 mm) on the atrial side of the prothesis consistent with multiple vegetations (Figure 1). The patient was hospitalized, and on admission, he had no symptoms, normal vital signs, and no heart murmurs, and no signs of endocarditis were observed.

Figure 1.

Transesophageal Echocardiogram Showing Multiple Vegetations on the Mitral Valve

The arrow points to vegetations on the mitral valve. LA = left atrium; LV = left ventricle.

Past Medical History

The patient had a history of mitral valve endocarditis (viridans group Streptococcus) and underwent mechanical MVR 8 years earlier. Furthermore, the patient was known to have hypertension, a history of appendectomy, and an allergy to amoxicillin.

Differential Diagnosis

The initial differential diagnosis included IE and thrombus of the mechanical mitral valve.

Investigations

Results of all blood cultures before and on admission were negative. Four days after the hospital admission, 1 of the blood cultures showed Enterococcus faecalis. Results of polymerase chain reaction testing for Coxiella infection, Whipple disease, syphilis, Bartonella infection, and tuberculosis were negative. The CRP at admission (52 mg/L) was increasing compared with a few days earlier (22 mg/L). There was no paravalvular leakage seen on TTE and TEE (Video 1). Positron emission tomography combined with CT showed increased fluorodeoxyglucose uptake around the mitral valve prosthesis, consistent with IE. Coronary angiography (CAG) as standard work-up for surgery showed “rocking motion” of the valve (Video 2). Cardiac CT angiography (CTA) showed thickened tissue around the mitral valve prosthesis consistent with IE with perivalvular extension. Furthermore, CTA showed large (±270° of the annulus) crypts at the posterior mitral annulus (Figures 2A to 2E) (Video 1). The findings on CAG and CT suggested a dehiscent mitral valve with extensive periannular abscesses; however, no paravalvular leakage was found on TEE. Despite the contradictory findings on imaging, there was an indication for surgery (1 major and 2 minor modified Duke criteria).

Figure2.

Computed Tomography and Positron Emission Tomography With Computed Tomography

(A) Sagittal plane showing multiple crypts around the mitral valve. (B) Axial plane. (C) Coronal plane. (D) Three-dimensional reconstruction. (E) Positron emission tomography with computed tomography showing high uptake. Ao = aorta; Cx = circumflex artery; PA = pulmonary artery; RV = right ventricle; # = crypt; other abbreviations as in Figure 1.

Management

Intravenous antibiotic treatment was started during admission, and the patient was scheduled for surgery after the foregoing investigations. Repeat sternotomy was performed, and patient was placed on bicaval cardiopulmonary bypass. Custodiol cardioplegia was administered to arrest the heart, and access to the left atrium was gained through an extended vertical transatrial septal incision (Guiraudon incision). We found large vegetations on the atrial side of the prosthesis (Figure 3A) and multiple crypts with vegetations (Figure 3B) after explantation of the prosthesis. Close inspection during surgery showed that these crypts were indeed infected; however, it appears that the MVR was implanted in an extra-annular location in the left atrial wall that created crypts mimicking periprosthetic abscesses (Figures 3C and 3F). The multiple crypts were closed with a pericardial patch (Figure 3D), and a new biological prosthesis was implanted (Figure 3E). Because of these findings, we concluded that these crypts were probably primarily related to the supra-annular placement of the MVR and not to the prosthetic valve endocarditis. The postoperative course of the patient was uncomplicated, and the length of the hospital stay after surgery was 14 days. Results of perioperative cultures (prosthesis and vegetations) showed the same E. faecalis as in the preoperative blood culture, thus confirming the diagnosis of prosthetic valve endocarditis. Antibiotic treatment was continued until 6 weeks after surgery.

Figure 3.

Intraoperative Findings

(A) Mechanical mitral valve prosthesis with vegetations. (B) View of the annulus after explantation of the mechanical valve, thus revealing the crypt with vegetations. The posterior mitral valve leaflet was preserved during previous surgery. (C and F) The multiple crypts were a result of supra-annular implantation of the prosthesis. The small dotted line is the true mitral annulus, and the long dotted line is the suture line of the previous implanted prosthesis. Between these 2 lines, vegetations were found in the crypt (#), formed by the indentations of a previously supra-annular implanted prosthesis. (D) Repair of the crypts with a bovine pericardial patch. (E) Result of repair and implantation of a new biological prosthesis. P2 = segment 2 of the posterior mitral valve leaflet; other abbreviations as in Figure 1.

Discussion

The diagnosis of IE with paravalvular extension is challenging, and this disease is often difficult to distinguish from other disorders such as supra-annular implanted MVR. For surgical planning, there were 2 extraordinary findings on imaging. First, imaging features were consistent with multiple periprosthetic abscesses, which are not common findings in IE (Figures 2A to 2E). Second, we found an abnormal rocking motion of the mitral valve prosthesis on CTA and CAG suggesting prosthesis dehiscence. Both findings could be caused by IE. However, IE as the primary origin of those abnormalities was considered less likely because there was no paravalvular regurgitation and because of the suspicion of multiple periprosthetic abscesses.

There are some case reports describing subvalvular abscesses after native mitral valve endocarditis,^1,2 as well as after MVR.³ However, all these reports described the presence of a single abscess. The mechanism is probably rupture of the mitral valve annulus, caused by infection or injury during placement of the annular sutures for the MVR. This will lead to a single abscess. Supra-annular placement of the sutures for MVR has been described in patients with a heavily calcified mitral annulus^4,5 and endocarditis⁶ in which the mitral annulus was not suitable for the placement of sutures. This implantation technique can lead to multiple smaller sutures mimicking extensive abscesses. The atrial tissue between the sutures and the mitral annulus will become part of the left ventricle, and the prosthesis will move during the heart cycle, just like a rocking valve, albeit without paravalvular leakage. This finding should have led us to suspect that the previous implantation of the mitral valve was supra-annular in the left atrium, rather than suspecting multiple abscesses.

Follow-Up

There were no signs for residual or recurrent infection after the end of antibiotic treatment after 6 weeks. (CRP, 2 mg/L; leukocyte count, 5.6 × 109/L). Currently, more than 2 years after the surgery, there are no signs of recurrent infection.

Conclusions

Our case report describes the course of a patient with IE with suspected multiple periprosthetic abscesses of the mitral annulus. IE with paravalvular extension is often difficult to distinguish from other disorders, such as supra-annular implanted MVR leading to multiple periannular crypts.

Funding Sources and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Appendix

Video 1

Transesophageal Echocardiogram Showing Multiple Vegetations on the Mitral Valvex

The arrow points to vegetations on the mitral valve. L

Video 2

Rocking Mitral Valve