Lambl Excrescences

Etiology

Lambl excrescences are slender filamentous processes that are neither sessile nor pedunculated. They occur on the endocardial surface where valvular cusps make contact with one another. Histologically, these are acellular, composed of a core made of fibro-elastic tissue covered by stroma, both densely hyalinized. This, in turn, is covered by a single layer of endothelium. They lack vasculature, hence are devoid of granulation tissue. Lambl excrescences are almost always found on either native or even prosthetic heart valves. Very rarely, strands may also be seen on sites other than heart valves, for example, papillary muscles, atrial septum, and chordae tendineae.[3][4]

Lambl excrescences can appear as a single strand or in a cluster. They are approximately 1 mm in diameter and can reach up to a length of 10 mm. The length is stunted due to their strategic location on the valvular cusps which exposes them to high stress, especially, when located on the aortic valve which is subjected to relatively higher pressures compared to other valves. Sometimes multiple adjacent excrescences adhere to each other forming “giant Lambl excrescences” which can grow up to a length of 2 cm. Despite some case reports of giant Lambl excrescences being associated with ischemic stroke, no clear evidence in medical literature shows a correlation between the size of the strand and the risk of the embolic event.[5]

Epidemiology

Of the general population referred for a transesophageal echocardiogram (TEE) for all indications, 5.5% have valvular strands, and the number drastically increases to 40% in patients referred for cryptogenic stroke. Lambl excrescences are detected in both adults and children. However, the prevalence is higher in adults than children and increases with age. On an echocardiogram, the prevalence peaks from age 61 to 70 and then falls after that due to aging heart valves getting more and more calcified resulting in underdetection of Lambl excrescences in relation to the calcified valves. Also, the incidence is relatively more common in men than women. Even though Lambl excrescences are reported to grow on all native and prosthetic valves, prevalence is more on the left-sided heart valves, aortic more than mitral. Lambl excrescences when asymptomatic and followed over several years, appear to remain stable and intact without significant morphological changes.

Pathophysiology

Pathogenesis is not entirely clear. Aortic and mitral valves are the two most common locations of Lambl excrescences. However, ischemic events were more commonly observed in association with the ones on aortic valves as com­pared to mitral valves. It is postulated that due to high stress from blood-flow jets causing shearing forces and trauma on the heart valves endocardium develops occasional tears. These tears occur on the valvular cusps at the coaptation site followed by fibrin deposition and small thrombi formation on endothelial injury and subsequent overgrowth of endothelium over extended periods of time with advancing age.

The pathogenesis of embolic phenomena causing distal organ ischemia and injury such as ischemic stroke, acute coronary syndrome, or pulmonary embolism remains unclear. While the possibility of Lambl excrescences breaking off and embolizing seems obvious; however, fragments of broken valvular strands are not usually seen in the target arteries of distal organs. There is substantial evidence suggesting only an association between Lambl excrescences and embolic events such as ischemic strokes and coronary syndromes. However, a direct causal relationship is not yet established.

History and Physical

Most cases of Lambl excrescences remain asymptomatic and are detected incidentally on echocardiography or on autopsy. These, especially when found on aortic valve cusps, have a higher potential of breaking off and embolize to distal organs usually in association with embolic strokes, coronary artery embolisms that result in acute coronary syndromes, or pulmonary embolisms. If large enough, even without embolization, these can cause mechanical valvular obstruction. Depending on the target distal organ affected patients can present with varied neurological and cardiopulmonary symptoms.

Patients can present with stroke-like features such as motor deficits, sensory deficits, aphasia, dysarthria, dysphagia, visual disturbances, cranial nerve palsies, and ataxia to name a few. Cardiopulmonary features such as chest pain, dyspnea, diaphoresis, syncope, dizziness, nausea, vomiting, hypoxia, hypotension, arrhythmias, ischemic changes on the ECG, and elevated cardiac biomarkers can also be present.

Evaluation

Transesophageal echocardiogram (TEE) is the gold standard in detecting Lambl excrescences, however, due to advancement in ultrasound technology the sensitivity of TTE has also increased significantly. Alternatively, when TEE is not feasible, a high-resolution CT scan can be done. TEE detects these valvular growths and also determines its attachment to the valves, its location in relation to other cardiac structures, and its mobility. Although an echocardiogram provides vivid details about the radiological morphology, a definitive diagnosis is still done through microscopic histopathological evaluation of the valvular strands when possible.

Echocardiographically, Lambl excrescences appear as thin, hypermobile, filiform strands on the valvular cusps’ line of closure. In the short-axis view, linear strands can be seen projecting from the ventricular aspect of the aortic valve cusp tips. In the long-axis view, these are seen in rows on all three aortic valve leaflets.

Treatment / Management

There are no clear evidence-based guidelines for the treatment of Lambl excrescences. The management is primarily based upon cases reported in the medical literature.

Various approaches, both pharmacological and surgical, have been described in the management of Lambl excrescences. Asymptomatic patients are best managed with close observation, and with serial follow-up echocardiograms. When associated with stroke, an exhaustive stroke workup to identify the potential cause of stroke should always be undertaken. This should include carotid duplex ultrasound, hypercoagulable workup, and a complete TEE assessing the ascending, transverse, and arch segments of the aorta. If the workup remains negative without any identifiable cause, then the patients can be treated with antiplatelet agents such as aspirin and clopidogrel/dipyridamole and/or anticoagulation with coumadin. In cases of recurrent strokes, when associated with Lambl excrescences, surgical excision may prove beneficial.

The choice between surgical debridement and conservative management depends on individual cases and their peri-operative risks. The efficacy and mortality benefit of any of these treatment measures have not been established yet.

Due to the lack of consensus, at this time it is difficult to exclude Lambl excrescences as a potential source of emboli in cryptogenic stroke. Medical providers should be aware of Lambl excrescences and at least keep them in the differential diagnosis of a patient with cryptogenic stroke unless ev­idence suggests otherwise. A TEE should always be a part of stroke workup in embolic stroke with unknown sources of emboli.

Differential Diagnosis

Lambl excrescences have to be differentiated from fibroelastomas, valvular vegetations, myxomas, cardiac thrombi, nonbacterial vegetations, other cardiac tumors, and metastases. All of these entities have a potential for embolization to a varying degree. Distinguishing between Lambl excrescences and vegetations or fibroelastomas can be quite challenging. Others are reasonably well-differentiated on echocardiogram.

Lambl excrescences are similar histopathologically to cardiac papillary fibroelastomas. The difference is that papillary fibroelastomas are larger, more gelatinous, usually found away from the line of valve closure, and covered by multiple layers of endothelial cells. Whereas, Lambl excrescences are smaller, located at the line of valve closure, and covered by a single endothelial layer. The growth of Lambl excrescences may be limited due to their exposed high-stress location. In contrast, fibroelastomas are usually found on the mechanically less pressured parts of valves and other parts of the endocardium. Thus, fibroelastomas are bulkier, can be attached to the valve through a stalk or pedestal, and their surfaces may contain multiple fingerlike projections. Because fibroelastomas are larger than Lambl excrescences, they are therefore more prone to embolization. It is generally recommended that fibroelastomas be surgically removed.

Endocarditis-related valvular vegetations are typically irregular masses that have a different echogenicity in relation to other cardiac structures. These vegetations can be adherent to valvular cusps at any site, are independent of valvular mobility, and can have other pathognomonic echo findings of infection such as abscesses and valvular dehiscence besides, a clinical history suggestive of infective endocarditis and valvular dysfunction.

Nonbacterial vegetations such as the Libman Sacks thrombotic vegetations again can be located on any part of the valvular cusp. These are somewhat rounded and nonpedunculated lesions that lack independent mobility.

Prognosis

Prognosis in asymptomatic incidental findings of Lambl excrescences is excellent. However, when these are associated with complications like ischemic stroke, acute coronary syndrome, and pulmonary embolism the prognosis is independent of etiopathogenesis. In other words, irrespective of the etiology and the pathogenesis, these complications carry the same prognosis as they do with other causes.

Complications

Most cases of Lambl excrescences remain asymptomatic. These only get complicated when they break off and embolize to distal organs like the brain, heart, and lungs. Embolic ischemic strokes, coronary embolisms causing acute coronary syndromes, and pulmonary embolisms if large enough are all complications associated with Lambl excrescences. Sometimes when they grow into giant excrescences, even without embolization, they can cause local mechanical valvular obstruction.[6][7][8]