In lymphangiomyomatosis (LAM), the characteristic histologic changes can be seen in the lungs, thoracic duct, and lymph nodes of mediastinum and retroperitoneum. In lungs, LAM shows proliferation of plump spindle-shaped myoid cells arranged in short fascicles around arterioles, venules, and lymphatics which cause thickening of alveolar septa. The tumor cells may invade lymphatics and blood vessel walls causing secondary hemorrhage and destruction of the septal wall. Over time, this results in formation of cystically-dilated airspaces (as seen here) creating a honecomb appearance grossly. The spindle cell proliferation can range from subtle and easily overlooked to overt tumor-like nodules.