Relevant anatomy and surgical technique
The preganglionic parasympathetic fibres to the nasal mucosa leave the facial nerve as the greater superficial petrosal nerve and are joined by sympathetic fibres (deep petrosal nerve) to become the vidian nerve. This passes through the vidian canal and enters the pterygopalatine fossa (PPF) where the parasympathetic fibres synapse in the sphenopalatine ganglion (SPG). The posterior nasal nerve is a branch of the SPG within the PPF and consists of postganglionic parasympathetic, sympathetic, and sensory fibres. It enters the nasal cavity via the sphenopalatine foramen together with the sphenopalatine artery (SPA) and supplies the nasal mucosa providing a secretomotor and vasodilatory stimulus as well as somatic sensory supply(7-8). Two major branches of the posterior nasal nerve are often found anteroinferior and posterosuperior to the SPA but there are variations in the number and location of these branches(9). They are often overlooked during an SPA ligation as they are embedded in the connective tissue surrounding the artery. Division of these branches specifically targets the nerve fibres destined to innervate the nose and spares the fibres that innervate the lacrimal gland.
There are variations in the surgical technique of PNN but in general the procedure involves raising a mucosal flap off the sphenopalatine foramen and SPA and identifying the nerve and any major branches(9). These are divided and partly excised, and this can be achieved without dividing the SPA(11). PNN is a relatively straightforward procedure, involves a less complicated dissection than vidian neurectomy(12), and can be carried out as a day case procedure.
Rhinitis is a heterogenous condition with multiple overlapping endotypes and aetiologies(10). An imbalance between parasympathetic and sympathetic stimulation can potentially be a contributory mechanism. Dividing the posterior nasal nerve rather than the vidian nerve could potentially improve symptoms without the lacrimal and maxillary nerve complications seen frequently in vidian neurectomy(13). It also divides the somatosensory fibres which could further contribute to reducing nasal hypersensitivity to stimuli such as cold air(9-10).