Location and Boundaries
The paired frontal sinuses are found within the frontal bone and are the most superior of the paranasal sinuses. They are usually separated by a bony septum and there may be other incomplete septum further dividing them. When viewed anteriorly, they are triangular in shape. The points of this triangle are:
- The top of the nasion
- A point 3 cm above the first
- The junction of the medial third and lateral two-thirds of the supraorbital ridge
The sinus may extend anteriorly within the supraorbital ridge and posteriorly along the orbital part of the frontal bone. The aperture which connects to the nasal cavity usually opens as a frontonasal recess (the middle meatus).
Medially, with the contralateral frontal sinus.
Superiorly, laterally and posteriorly with the frontal bone and frontal lobe.
Inferiorly with the orbit.
The sinus is lined by pale pink mucosa.
Respiratory epithelium is a pseudostratified columnar type. Cilia are present near the aperture that connects the sinus with the nasal cavity.
The sinuses are fixed within the bone and do not move with physiological functions. They may be different sizes or shapes on each side. Hyperplasia of the sinus epithelium may occur with chronic inflammation
The size and shape of the sinuses vary considerably between different people. This variation is even used to identify bodies in forensic cases if radiological imaging of the sinuses is available. The aperture to the nasal cavity is variable in size and positioning.
Men usually have more prominent sinuses which gives their forehead more obliquity than females and children. The frontal sinuses usually begin to form after birth and are well developed by the age of 8.
Blood is delivered to the frontal sinuses via the supraorbital and anterior ethmoidal arteries.
Blood drains through an anastamotic vein to the supraorbital notch, where it returns to the heart via supraorbital and superior ophthalmic veins.
Lymph vessels from the frontal sinus pass to submandibular nodes
The sinuses receive general sensory input from branches of the supraorbital nerve (V) and secretomotor input from the pterygopalatine ganglion (via VII).
Routes of Cancer Spread
Sinus tumours are frequently locally aggressive but only uncommonly metastasize to nodal groups and even more rarely to distant sites. The frontal sinus is the site of origin in less than 1% of cases of sinus tumours.
Bony destruction is common most sinus tumours. In the frontal sinus, this may lead to invasion of the anterior cranial fossa, the orbit, the ethmoid sinuses, or the soft tissues of the face.
The submandibular nodes are most frequently affected in lymphatic spread from the frontal sinuses.
Haemotogenous spread is unusual with squamous cell carcinoma (the most common aetiology).
Invasion of the cranial nerves may occur. The supraorbital branch of the trigeminal is the usual nerve involved.