Two ganglionic cell groups, located close together and called the internal carotid ganglion, not described before in man, were demonstrated extradurally on the ventrolateral surface of the human internal carotid artery (ICA), where the greater superficial petrosal nerve is joined by the (greater) deep petrosal nerve to form the vidian nerve. The two ganglionic cell groups have fiber connections to the ICA, and consist of 50-70 cells each. By immunohistochemistry the majority of cells in one of the groups were shown to contain vasoactive intestinal polypeptide (VIP) and choline acetyltransferase (ChAT) indicating a parasympathetic function, whereas most cells in the other group contained substance P (SP) and possibly calcitonin gene-related peptide (CGRP), transmitters in pain fibers. Lateral to the intracavernous segment of ICA 10-150 scattered or aggregated VIP- and ChAT-positive cells were found, with fiber connections to the ophthalmic nerve, the ICA, the abducent nerve and the sphenopalatine ganglion. These cells may represent aberrant parasympathetic (sphenopalatine) ganglia, here referred to as cavernous ganglion. By radioimmunoassay substantial amounts of VIP, SP and CGRP were measured in both the extradural and the intracavernous segment of the ICA. Thus, the intracranial segment of the ICA is most likely innervated by parasympathetic and pain fibers from the internal carotid ganglion, sensory fibers from the ophthalmic division of the trigeminal ganglion, and parasympathetic fibers from the sphenopalatine and/or cavernous ganglion. Clinical implications for the activation of these nerves to cause pain, dilatation and edema in this segment of the ICA during attacks of cluster headache and painful ophthalmoplegic syndromes are discussed.
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