Prosthesis with branched portion

A prosthesis, comprising:

• a tubular graft body including a sidewall extending between an inflow end and an outflow end and defining a main lumen between the outflow and inflow ends;
• a stent structure coupled along the graft body;
• a trough extending from the sidewall and comprising:
• a first trough wall composed from a portion of the sidewall of the tubular graft body,
• a first trough wall boundary bounding the first trough wall, the first trough wall including a first end, a second end longitudinally spaced from the first end, and first and second edges between the first and second ends, and
• first and second opposed outer trough walls attached to the first trough wall along the first and second edges of the first trough wall boundary and extending outwardly from the first trough wall, and
• a trough boundary;
• and
• a tubular branch defining a branch lumen and extending from the trough towards one of the inflow or outflow ends of the graft body, wherein the trough, the branch lumen, and the main lumen are in fluid communication, and wherein the first trough wall presents a continuous surface to the branch lumen.