Lambl's excrescences and fibrous strands

The serpentine mitral valve and cerebral embolism

James Ker

Cardiovascular Ultrasound 2011, 9:7 

 

Vilem Dusan Lambl, a Bohemian physician (1824-1895) were the first to describe the occurrence of small, filiform processes he observed on the aortic valve in 1856[5] . Today, these Lambl's excrescences are also referred to as valvular strands and have been observed on all native and prosthetic valves[5] . These strands may occur as single strands, in rows or even in clusters[5] . They can vary in length from 1 mm to 10 mm and are usually less than 1 mm in thickness[5] .

Valvular strands are composed of a fibroelastic, avascular core, covered by a layer of endothelial cells[5,6] .

The exact pathogenesis of formation of these structures are still unclear, however current opinion is that the initiating factor is that of an endocardial lesion in areas of trauma and/or high shear stress[5,6] . These denuded areas are then covered by fibrin with subsequent covering by an endothelial layer[5,6] . The prevalence of valvular strands has been estimated as 5.5% in a general population referred for transesophageal echocardiography and 40% in patients with stroke of unknown cause[1,2] .

The differential diagnosis for valvular strands includes the following[5] : a myxoma, thrombi, valvular vegetations, nonbacterial thrombotic (marantic) endocarditis, cardiac metastases, a fibroelastoma and other primary cardiac neoplasms.

Of all of the above, the most difficult distinction is that between a valvular strand and a fibroelastoma[5,7] . Histologically, these two entities are very similar with both containing a central core of elastic connective tissue, covered by endothelium. However, valvular strands are covered by a single layer of endothelial cells, but fibroelastomas contain regions of multiple layers of endothelial cells[5,7] .

Echocardiographically, fibroelastomas are more bulky, with stalks or pedestals sometimes present and multiple, fingerlike projections on their surface[5] . As fibroelastomas are usually found on the mechanically less strained parts of valves and endocardium they tend to be larger than valvular strands[5] . Valvular strands (Lambl's excrescences) are always found on the affected valve's line of closure and this limits their growth[5] .

Several published case reports have shown that valvular strands are associated with emboli to the coronary, pulmonary, spinal, retinal and cerebral circulation[1] .

Specifically regarding stroke, numerous reports have demonstrated an association with valvular strands, particularly in young patients[3,4,8,9] . The mechanism for embolic events is either that of thrombi forming on the strands which then embolize or it is possible that the valvular strand itself can embolize[2] . Direct visualization of thrombus on a valvular strand have indeed been described before[10] .

In conclusion, a case of a valvular strand, attached to the coapting edge of the mitral valve is presented, giving a serpentine appearance to the mitral valve. This valvular strand was the cause for a cerebral embolism which presented with a transient right sided hemiparesis. This is the only current case in the literature, where the combination of aspirin and clopidogrel is used for the prevention of further episodes of cerebral embolism. In the only randomized treatment study to date, no difference in relation to efficacy of warfarin compared to aspirin was found in patients with valvular strands and previous embolic episodes[2] . For this reason a combination of antiplatelet therapy was initiated as a therapeutic trial.

It is proposed that a randomized controlled study involving the combination of aspirin and clopidogrel is warranted in patients with valvular strands presenting with a first episode of cerebral embolism.

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2. Stroke 2004, 35:1436-1442.

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10. Arch Neurol 1997, 54:41-44.