Pathology of the Head and Neck

306 M.R. Canninga-Van Dijkand fat in the earliest stages. This will be followed bylymphocytic infiltration and end with fibrous changes.In cases of massive infiltration by lymphocytes, immunohistochemistryis necessary to rule out malignantlymphoma (Fig. 10.30). Another disease that canmimic pseudotumours is sarcoidosis. Sarcoidosis ishistologically characterised by typical granulomas, notsurrounded by lymphocytes.10Fig. 10.30. Pseudotumour of the orbit: fibrous tissue with necroticfat cells is infiltrated by large groups of lymphocytes. Immunohistochemistryis necessary to rule out a malignant lymphomasive bony destruction of the orbital walls with associatedorbital cellulitis. In patients with poorly controlleddiabetes, but also in immunocompromised patients,orbital cellulitis can also be caused by fungal agents,for example mucormycosis. Presenting symptoms mostfrequently include oedema of the upper eyelid, headacheand facial pain. Sometimes it can be asymptomatic.Clinically, orbital cellulitis is of great importance,as it is a severe disease with potentially disastrous consequences.Despite antifungal or antibacterial therapy,disease can progress. It may lead to optic neuritis, opticatrophy, blindness, cavernous sinus thrombosis, intracranialabscess formation, meningitis, subdural empyema,and even death. An incision biopsy of the processcan be helpful in the diagnostic work-up. Histology willshow an extensive neutrophilic infiltration of the orbitalfibrous tissue and fat. The causative microorganismscan often be found with PAS, Gram and silver stainings.It is important for the pathologist to look for underlyingcauses, like tumours.10.8.1.3 PseudotumourNon-specific inflammation of orbital tissues is knownas orbital pseudotumour. It tends to be unilateral andaccounts for 25% of all cases of unilateral exophthalmos.Spontaneous regression can occur and a responseto steroids is often seen. However, orbital pseudotumourscan also be chronic and progressive. The diagnosishas to be confirmed by an incision biopsy, especiallyin cases in which the pseudotumour appearsas a discrete mass and simulates a neoplastic lesion.Histology shows oedema of the orbital fibrous tissue10.8.2 Tumoursand Tumour-Like ConditionsA variety of tumours and pseudotumours can involvethe orbit. Most orbital lesions are benign (65%). The percentageof malignant tumours increases with age, with60% of malignancies in patients over 60 years of age, becauseof the higher incidence of lymphoma and metastatictumours in the elderly. Orbital tumours of childhoodare distinct from tumours that occur in adults. Manyare congenital with early presentations. Most paediatricorbital tumours are benign (80%); developmental cystscomprise half of orbital cases, with capillary haemangiomabeing the second most common orbital tumourin children. The most common orbital malignancy inchildren is rhabdomyosarcoma. Whereas the malignanttumours may be life-threatening, both malignant andbenign tumours may be vision-threatening. Almost alllymphomas, soft tissue and bone tumours may involvethe orbit.10.8.2.1 Developmental CystsEpithelial rests found at sutural sites within the orbitcan give rise to epithelial cysts. Cysts of the surfaceepithelium are further divided into simple epithelialcysts (epidermal, conjunctival, respiratory and apocrinegland), and dermoid cysts (epidermal and conjunctival).Epidermal dermoid cyst (dermoid) is by far the mostcommon orbital cystic lesion in children, accountingfor over 40% of all orbital lesions of childhood. Otherdevelopmental cysts are teratomatous cysts, neural cysts(congenital cystic eye and colobomatous cyst) and thoseassociated with brain and meningeal tissue (encephaloceleand optic nerve meningocele) [103]. Developmentalcysts have to be differentiated from secondary cysts, likemucocele and inflammatory cysts. Mucocele can occurin children with cystic fibrosis. Inflammatory cystsare generally due to parasitic infestations and are morecommon in tropical areas of the world. Furthermore,non-cystic tumourous lesions with a cystic component(like rhabdomyosarcoma and lymphangioma) can presentas a cyst.