Mesenteric Vascularized Lymph Node Transfer

Key Points

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The small bowel mesentery represents a donor site for vascularized lymph node transfer that contains numerous and redundant lymph nodes and has reliable anatomy with minimal donor site morbidity.
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The small bowel mesenteric lymph node flap can usually be readily outlined before flap harvest through the use of transillumination, including its lymph nodes, their relationship to the vascular pedicle, and the remaining vascular supply to the bowel.
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The mesentery of the proximal third of the jejunum contains the greatest number of lymph nodes.
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Use of peripherally located lymph nodes has the advantage of better vascular inflow and outflow balance, with smaller vessels and a relatively greater capillary bed connecting the arterial inflow and venous outflow. In contrast, lymph nodes located toward the root of the mesentery are adjacent to much larger feeding vessels, which primarily supply the bowel and may require the creation of an arteriovenous loop at the distal end of the vascular pedicle or a flow-through flap inset to maintain adequate balance between arterial inflow and venous outflow.

Introduction

Vascularized lymph node transfer (VLNT) entails the microsurgical transfer of lymph nodes from a donor site to an area with lymphedema. In contrast to lymphovenous bypass surgery, VLNT can also be applied to cases of lymphedema where no suitable lymphatics are available for anastomosis, such as in patients with more advanced disease. The transferred lymph nodes in VLNT are hypothesized to improve lymphedema by acting as a surgical wick to bridge a zone of obstruction of lymphatic drainage and as a lymphatic pump that absorbs interstitial fluid and returns it to the systemic circulation.

Several different VLNT donor sites have been described, including the omentum, groin, thoracic/axillary, submental, and supraclavicular regions. The characteristics of an ideal donor site for VLNT include the ability to transfer several lymph nodes on a single vascular pedicle, reliable anatomy, minimal donor site morbidity (including the risk of donor site lymphedema), feasibility in majority of patients, and an inconspicuous scar. The jejunal mesentery is a donor site that possesses these characteristics and represents an important option for the treatment of lymphedema with VLNT.

Anatomy

The jejunum is the middle segment of the small intestine and functions primarily in the digestion and absorption of enteric contents. It comprises approximately two-fifths of the total length of the small intestine and itself measures roughly 2.5 m in length. The mesentery, which is a double fold of the peritoneum, suspends the small and large intestines from the posterior abdominal wall and houses their vascular, lymphatic, and nervous supply.

The jejunum receives its blood supply from the superior mesenteric artery (SMA), which originates from the aorta anterior to L1 and approximately 1 cm inferior to the takeoff of the celiac artery. From there, the SMA proceeds inferiorly, passing behind the neck of the pancreas and the splenic vein, before giving rise to several jejunal arteries, which run in parallel to each other within the layers of the mesentery. As these vessels travel toward the small intestine, the jejunal arteries further divide into branches that have numerous anastomoses with adjacent branches to form a series of arterial arcades. The collateral flow conferred by these anastomoses serves as the basis for the ability to selectively divide mesenteric branches without causing ischemia. The venous drainage of the small intestine occurs through the superior mesenteric vein, which ultimately joins the splenic vein to empty into the portal system.

Cadaveric investigation has found that the greatest number of lymph nodes exist within the proximal third of the jejunum, where there is an average of 19.2 total lymph nodes, a significantly greater number than in the middle and distal thirds. The lymph nodes can be divided into those located in the periphery of the mesentery closer to the bowel and the more plentiful nodes located centrally and closer to the larger vessels at the root of the mesentery. The lymph nodes present in the periphery are usually supplied by vessels that measure approximately 1.5–3 mm in diameter (with the vein measuring approximately 0.5 mm larger than the associated artery) and include a more robust capillary network around the lymph nodes, making them an ideal target for a standard end-to-end or end-to-side anastomosis at the recipient site. The arterial inflow and venous outflow should be well balanced in these flaps as they represent more of an “end organ” to the pedicle, not unlike other fasciocutaneous flaps that we routinely use, such as the anterolateral thigh flap. However, these peripherally located lymph node flaps may include the anastomotic loops and straight arteries to the jejunum and thus may potentially devascularize a segment of the bowel and should be carefully chosen by transillumination accordingly. Use of these relatively smaller vessels for microsurgical transfer, compared to those in closer proximity to the root of the mesentery, achieves a better size match with the flap itself, which typically measures approximately 3 cm.

The lymph nodes located toward the root of the mesentery can be harvested with less concern about relative bowel ischemia due to the tremendous arborization and redundant vascular connections through anastomotic loops toward the periphery of the mesentery. However, the larger vessels at the mesenteric root (the artery and vein typically measure 3+ and 4–6 mm, respectively) carry a tremendous amount of blood to and from the jejunum, which largely bypasses the small capillary perforators to the lymph nodes in this area. Therefore, a standard end-to-end vascular connection of the flap pedicle to donor vessels at the recipient site may result in a significant vascular inflow and outflow imbalance and even flap loss, unless a more physiologic connection, such as a flow-through design of the flap artery and vein or an arteriovenous loop at the distal end of the flap pedicle, is included.

Preoperative Evaluation

A thorough history, including prior surgery of both the abdomen and the affected limb, is obtained. A commonly encountered prior surgical history of the abdomen is, in most cases, unlikely to impact the feasibility of performing jejunal mesenteric vascular lymph node transfer, in contrast to the omental flap. The specific site on the affected limb for lymph node transfer is based on consideration of both previous treatment history and the location of lymphedema. In the upper extremity, the wrist or the forearm is chosen as the recipient site if lymphedema is more severe in the hand and forearm than in the upper arm. Alternatively, the axilla is selected if the complete upper extremity is involved with lymphedema or if there is a significant amount of scarring in the axilla. In the lower extremity, we recommend the groin as the site of lymph node transfer if the patient has had a previous inguinal node dissection and the distal leg if the patient has had a previous peri-aortic or deep pelvic lymph node dissection and the inguinal nodes are intact. In cases where there is significant scarring at the site of the proximal node dissection and lymphedema that primarily affects the distal extremity, we will consider a simultaneous double-level lymph node transfer with proximal scar release.

We typically instruct our patients to ingest a milk shake or a fatty meal the night before surgery as this results in a milky white lymph outlining all of the lymphatics from the small bowel toward the mesenteric lymph nodes, thereby facilitating the identification of afferent and efferent lymphatics for possible lymphatic-to-lymphatic anastomosis at the recipient site, if desired.

Operative Technique

Mesenteric jejunal VLNT is performed through a supraumbilical vertical midline incision measuring 4–7 cm in length. The proximal third of the jejunum is identified and delivered from the abdomen onto the surgical field. Palpation, inspection, and transillumination are utilized to determine the location and quantity of lymph nodes and their associated vasculature ( Fig. 18.1 ). Once a set of nodes are chosen that have vessels suitable for microvascular anastomosis, one side of the mesentery is scored with electrocautery around the distal periphery of the flap. Distal vascular branches seen beneath this layer are then ligated. The flap is then elevated by dissecting the desired group of nodes and a superficial layer of mesentery from the deep layer of mesentery. The corresponding vascular supply is then mobilized from distal to proximal toward the root of the mesentery. The deep layer of the mesentery is preserved throughout flap harvest in order to prevent the development of an internal hernia. Dissection continues until vessel caliber and pedicle length are adequate for microvascular anastomosis. A pedicle length of approximately 3–5 cm can usually be obtained, with arterial and venous diameters typically measuring 1–2.5 mm in the periphery, and much larger toward the root of the mesentery as outlined earlier.