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).