Table 1.

Classification System of Temporal Bone Paragangliomas

IAM, internal auditory meatus; CPA, cerebellopontine angle.
Class A	Tumors arise along the tympanic plexus on the promontory of the middle ear. Blood supply is from the tympanic artery, a branch of the ascending pharyngeal artery. They produce minimal erosion of the promontory.
Class B	Tumors originate in the canalis tympanicus of the hypotympanum and invade the middle ear and mastoid. The carotid foramen and canal are intact. These tumors invade bone, but the cortical bone over the jugular bulb is intact. The distinction between class B tumors and a C1 tumor may be difficult.
Class C	Tumors arise in the dome of the jugular bulb and destroy the overlying cortical bone. They spread inferiorly along the jugular vein and lower cranial nerves, posteriorly into the sigmoid sinus, superiorly toward the otic capsule and IAM, laterally to the hypotympanum and middle ear, medially to the jugular foramen and CPA.
	Subclassification is made according to the degree of erosion of the carotid canal:
	• C1: erode carotid foramen but do not invade the carotid artery
	• C2: destroy the vertical carotid canal between the carotid foramen and carotid bend
	• C3: grow along the horizontal portion of the carotid artery but do not reach the foramen lacerum
	• C4: grow to the foramen lacerum and along the carotid artery to the cavernous sinus
Class D	Tumors that have intracranial extension are further subclassified as follows:
	• De: intracranial but extradural:
	De 1: displace posterior fossa dura < 2 cm
	De 2: displace posterior fossa dura > 2 cm
	• Di: intracranial with intradural extension:
	Di 1: intradural extension < 2 cm
	Di 2: intradural extension > 2 cm
	Di 3: intradural extension that makes the tumor unresectable