The present invention provides an endoscopic apparatus reversibly insertable into a curved lumen of a patient, comprising: a. a flexible sleeve characterized by a proximal end and a distal end said distal end of said flexible sleeve comprising: i. a flexible folded sleeve part comprising a portion of said flexible sleeve in a compact and folded arrangement said compact and folded sleeve portion unfolds and evert said folded sleeve part is characterized by a predetermined length Lfold ii. an unfolded sleeve portion in communication with said compact folded sleeve part, characterized by a length Lunfold Lunfold increases as at least a portion of said compact and folded sleeve portion unfolds and everts wherein said compact and folded sleeve portion is enclosed and within said folded sleeve part such that a single topologically cylindrical sleeve is provided
