Pathology of the Head and Neck

Eye and Ocular Adnexa Chapter 10 293tory, bilateral thinning of the central corneal stromaleads to severe astigmatism. Aetiology and pathogenesisare unclear. At histological examination the epitheliumcan be either atrophic or hyperplastic. The most strikingfinding is interruption of Bowman’s membrane, withdowngrowths of epithelium or upgrowths of cornealstroma in the breaking spot. The breaks may be narrowand the pathology is often restricted to a narrow 1–2 mmzone, sometimes serial sections are required to find thelesion. At the edge of the conus, iron can be found in theepithelium (Fleischer’s ring). The axial stroma showsmucoid degeneration, the peripheral stroma is of normalappearance. In severe cases, rupture of Descemet’smembrane and the endothelium can occur, resulting inan inflow of water and the appearance of cystic spaces.Keratoconus can be treated by surgery with use of stromalcornea grafts.10.3.3 Hereditary Corneal DystrophiesCorneal dystrophies are inherited, bilateral disordersthat can be divided into epithelial, stromal and endothelialabnormalities. Routine stains for suspected cornealdystrophy must include PAS, Masson, Alcian blue,Congo red and Trichrome stains. In end-stage dystrophiesa keratopathy can develop, in which all layers ofthe cornea are involved. Many patients with cornealdystrophies have a point mutation in a gene on chromosome5q31 [54, 77, 113].10.3.3.1 Epithelial DystrophiesEpithelial corneal dystrophies are Cogan’s microcysticdystrophy, Meesman’s dystrophy and Reis-Buckler’sring dystrophy [123]. The epithelial dystrophies presentwith photophobia and/or foreign body sensation.The most common form of epithelial dystrophy isCogan’s microcystic dystrophy, affecting females ofmiddle age. A thickened and folded basement membranewith epithelial cysts containing necrotic debrisis characteristic. Bowman’s membrane is not involved.In Meesman’s dystrophy small layers of the basementmembrane can be found between the epithelial cells.Reis-Buckler ring dystrophy is a bilateral, autosomaldominant dystrophy, not only affecting the epithelium,but also the anterior corneal stroma. The epithelium isoedematous and atrophic, Bowman’s membrane is interruptedand the anterior stroma contains abnormalfibrous tissue. Histology is not specific and transmissionelectron microscopy, which will show electrondenserods in the superficial stroma, is necessary toconfirm the diagnosis [87].10.3.3.2 Stromal Dystrophies10.3.3.2.1 Granular DystrophyGranular dystrophy is an autosomal dominant disorder,presenting in early childhood with discrete, opaquegranules in the otherwise transparent anterior cornealstroma. Histologically, non-birefringent hyaline bodiesare present in the stroma. The deposits are strongly positivewith Masson stain [67].10.3.3.2.2 Lattice DystrophyLattice dystrophy is an autosomal dominant disorder, clinicallypresenting in early childhood (type I) [66] or in the2nd decade (type II) [95] with linear opacities. Histologically,eosinophilic deposits are found in the corneal stroma.They consist of amyloid and are strongly Congo red-positive[67, 112]. The disease is treated by keratoplasty.The presence of amyloid in the corneal stroma canalso be seen in chronic inflammatory conditions, thesesecondary amyloid deposits should not be confused withlattice dystrophy.10.3.3.2.3 Avellino DystrophyA combined granular-lattice dystrophy with both hyalineand amyloid deposits in the corneal stroma was firstdescribed in the Italian village of Avellino [29].10.3.3.2.4 Macular Corneal DystrophyMacular dystrophy presents in childhood as a bilateralprocess with irregular opacities between cloudy cornealstroma. It is a disease disabling vision, inherited as anautosomal recessive trait. The disease is considered to bea localised metabolic disorder with production of excessiveamounts of acid mucopolysaccharide by fibroblasts[24, 67]. The disease is not associated with systemic mucopolysaccharidoses.10.3.3.3 Endothelial Dystrophies10.3.3.3.1 Fuchs DystrophyThis disorder affects elderly patients and is quite commonin routine histopathology. It presents clinicallywith bilateral diffuse cloudy and oedematous stroma.Histologically, the corneal epithelium is oedematous,