Pathology of the Head and Neck

40 A. Cardesa · L. Alos · A. Franchi22.1 Introduction2.1.1 EmbryologyThe midface, or area between the upper lip and forehead,develops at between 4 and 8 weeks’ gestation [219]. Thefrontal prominence forms during the 4th postovulatoryweek and gives rise to the superior and middle portionsof the face. The maxillary and nasal swellings form beneaththe frontal prominence. At the end of the 4th weeksurface thickening of the nasal swellings forms the nasalplacodes, which are of ectodermal origin and give riseto the epithelial lining of the nasal cavity and paranasalsinuses. The placodes invaginate, producing the nasalpits that become the anterior choanae (nostrils) and,less superficially, the primitive posterior choanae. Themedial nasal and frontal processes give rise to the nasalseptum, frontal bones, nasal bones, ethmoid sinus complexesand upper incisors. The lateral nasal and maxillaryprocesses fuse to form the philtrum and columella.The cartilaginous nasal capsule forms deep to the nasaland frontal bones from the chondrocranium (skull base)during the 7th and 8th postovulatory weeks. The paranasalsinuses develop from the lateral nasal walls at the6th foetal week, and their growth continues after birth,throughout childhood and adolescence.2.1.2 AnatomyThe nasal cavities are separated by the nasal septum,and limited by a roof, which is formed by the cribriformplate of the ethmoid, and a floor, which is formed by thehard palate [261]. The lateral walls have three turbinatesor conchae, and three horizontal spaces, or meatus, oneach side. The nasolacrimal duct opens in the inferiormeatus, whereas the middle meatus receives drainagefrom the frontal, anterior ethmoid and maxillary sinuses.Below the superior turbinate is the sphenoethmoidrecess, with the openings of the sphenoid and posteriorethmoid sinuses. Each nasal cavity communicates posteriorlywith the nasopharynx through the choanae.The paranasal sinuses are a group of cavities within thecorresponding craniofacial bones (maxilla, sphenoid,ethmoid and frontal) that communicate with the nasalcavities through an ostium.2.1.3 HistologyThe nasal vestibule and skin share a similar histology.At the level of the limen nasi, the keratinising squamousepithelium gradually changes first to cuboidal or columnarepithelium, and then to ciliated respiratory-type epithelium,which lines most of the nasal cavity and all theparanasal sinuses, with the exception of the roof [261].Numerous goblet cells are interspersed in the respiratory-typeepithelium. The lamina propria contains severalseromucous glands, lymphocytes, monocytes, anda well-developed vascular network, particularly evidentin the inferior and middle turbinate. The olfactory epitheliumis predominantly made of columnar non-ciliatedsustentacular cells, with scattered bipolar sensoryneurons and basal cells.2.2 Acute and Chronic Rhinosinusitis2.2.1 Viral Infections (Common Cold)Infectious rhinitis is typically viral and is often referredto as the “common cold”. It is more common in childrenthan in adults, and the most frequently identified agentsare rhinovirus, myxovirus, coronavirus and adenovirus[67, 271]. Swelling of the mucosa may cause obstructionof a sinus ostium, with subsequent secondary bacterialinfection (acute bacterial sinusitis). The histologic findingsinclude marked oedema and a non-specific mixedinflammatory infiltrate of the lamina propria.2.2.2 Bacterial InfectionsBacterial rhinosinusitis usually follows a viral infectionor allergic rhinitis, and the most commonly involvedagents are Streptococcus pneumoniae, Haemophilusinfluenzae and Moraxella catarrhalis [11, 34]. A denseinflammatory infiltrate mainly made of neutrophils occupiesthe lamina propria. Acute bacterial rhinosinusitisusually resolves with antibiotic therapy. Complicationsare rare and include contiguous infectious involvementof the orbit or central nervous system.2.2.3 Allergic RhinitisAllergic rhinitis (hay fever) is part of an inherited syndrome,which may also manifest as atopic eczema andasthma. In allergic rhinitis, airborne particles, such asgrass pollens, moulds and animal allergens, are depositedon the nasal mucosa giving rise to acute and chronicreactions. Allergens combine with the IgE antibodiesproduced by the plasma cells of the nasal mucosa,which are avidly bound to the Fc-epsilon receptors onmast cells. This triggers degranulation of mast cells andreleases the inflammatory mediators of the type I hypersensitivityreaction, causing rhinorrhoea and nasal obstruction.Microscopically, the nasal mucosa shows numerouseosinophils, abundant plasma and in some casesan increased number of mast cells. There is goblet cell