In this example, branching structures (broad papillae) are embedded in a dense fibrous stroma.
The lining cells are quite bland. Sometimes hemosiderin and cholesterol clefts are present.
This is a different example. The papillae are lined by a single layer of cuboidal epithelium, some with vacuolated cytoplasm and prominent membranes. These tumor usually stain for keratin, vimentin, and epithelial membrane antigen.
The papillary fronds grow into open spaces; the papillary cores are vascularized. This is very vascular tumor, and the bleeding into surrounding structures is not uncommon.
The endolymphatic duct runs from inner ear to the posterior surface of the petrous bone, ending beneath the dura as a flattened pouch called the endolymphatic sac. This sac is filled with endolymph and is involved in pressure regulation, sense of balance and equilibrium.
Tumors arising from the endolymphatic duct or endolymphatic sac are benign, however, they are locally invasive and thus, can cause hearing loss, tinnitus, vertigo, aural fullness and facial nerve dysfunction. These tumors are rare and can occur sporadically. However, most cases are found in association with von Hippel Lindau, in which case, they tend to be bilateral (Lonser).
Histologically, endolymphatic sac tumors are composed of papillary structures embedded in a fibrous stroma. The cores of the papillae are vascular, and the lining cells are generally cuboidal or flattened. Focally, there can be clear cell change with prominent membranes. There should only be mild pleomorphism and no mitotic activity. Often, there will be focal invasive destruction of surrounding bone.
Complete resection is the required treatment.
While benign, these are slow growing tumors that can invade and destroy bone and soft tissues aggressively.