Lambl’s excrescences, a histological term describing rare cardiac growths that develop at the valvular coaptation sites of the heart which are seen as thin, hypermobile, filiform strand on an echocardiogram. These filiform strands can be noted on echocardiogram either incidentally or in association with serious complications such as embolic stroke or acute coronary syndromes after they break off and embolize to distant organs.
Lambl’s excrescences are named after a Bohemian physician-scientist, Vilem Dusan Lambl (1824–1895) who first described these filiform growths on the aortic valve in 1856 in a paper titled, Papillare exkreszenzen an der semilunar-klappe der aorta (Weiner medicinische Wochenschrift). Approximately a century later, F. Margarey further described and differentiated these structures histopathologically.
Of note, Vilem Dusan Lambl also takes credit for the first original description of parasite which is named after him, Giardia lamblia. He scientifically described this parasite in microscopic drawings. He also credited for giving an initial description of the morphology of bladder cancer cell and spondylosis.
Lambl’s 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 is, in turn, is covered by a single layer of endothelium. They lack vasculature, hence are devoid of granulation tissue. Lambl’s 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.
Lambl’s 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’s excrescences” which can grow up to a length of 2 cm. Despite some case reports of giant Lambl’s 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.
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’s excrescences are detected in both adults and children. However, the prevalence is higher in adults than children and increases with age. On 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’s excrescences in relation to the calcified valves. Also, the incidence is relatively more common in men than women. Even though Lambl’s 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’s excrescences when asymptomatic and followed over several years, appear to remain stable and intact without significant morphological changes.
Pathogenesis is not entirely clear. Aortic and mitral valves are the 2 most common locations of Lambl’s 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’s 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's excrescences and embolic events such as ischemic strokes and coronary syndromes. However, a direct causal relationship is not yet established.
Most cases of Lambl’s 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 results 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, ataxia to name a few. And 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.
Transesophageal echocardiogram (TEE) is the gold standard in detecting Lambl’s 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 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’s 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.
There are no clear evidence-based guidelines for treatment of Lambl’s 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’s excrescences. Asymptomatic ones 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’s 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 has not been established yet.
Due to the lack of consensus, at this time it is difficult to exclude Lambl’s excrescences as a potential source of emboli in cryptogenic stroke. Medical providers should be aware of Lambl’s 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 source of emboli.
Lambl’s 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’s excrescences and vegetations or fibroelastomas can be quite challenging. Others are reasonably well-differentiated on echocardiogram.
Lambl’s 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’s excrescences are smaller, located at the line of valve closure, and covered by single endothelial layer. The growth of Lambl’s 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’s 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 in asymptomatic incidental findings of Lambl's 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.
Most cases of Lambl’s excrescences remain asymptomatic. These only get complicated when they break off and embolize to distal organs like 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’s excrescences. Sometimes if they grow into giant excrescences even without embolization can cause local mechanical valvular obstruction.
Lambl’s excrescences, once noticed on a routine echocardiogram, require a cardiology consultation for a TEE to identify, characterize, and differentiate from other similar structures. A neurology consultation would undoubtedly be beneficial when associated with an embolic ischemic stroke.
In summary, Lambl’s excrescences are uncommon cardiac valvular strands now more frequently detected even on routine transthoracic echocardiograms due to advancements in ultrasonography technology. These filiform strands can be an incidental finding or can be associated with severe complications like ischemic stroke, coronary embolism, pulmonary embolism, or valvular obstruction. There is no direct, causal relationship between Lambl’s excrescences and these complications. It is only a clinical association. When detected, their proper identification and differentiation from other similar pathological entities are essential. When complications such as embolic stroke occur, a thorough workup to identify the source of emboli should be performed. Lambl’s excrescences should be a potential but last consideration in cryptogenic strokes, when associated. Various treatment modalities have been tried including observation, antiplatelet therapy, anticoagulation, and surgical excision. However, at this time, there are no specific evidence-based guidelines to assist medical professionals in the long-term management of such patients. Further systemic studies are needed.
With further medical technological advancements, Lambl’s excrescences have a higher potential of detection and, therefore, a higher risk of incidence and prevalence.