 
40 to 50 % of lacrimal
masses are epithelial tumors mostly involving the orbital lobe. Among
those pleomorphic adenomas or mixed tumors are the most common.
Slow-growing processes, they occur in middle aged patients, are well
circumscribed and may present local recurrence if not completely
excised (fig. 32). Malignant transformation= must be suspected if
calcifications, bone erosion or infiltrative appearance are shown on CT
or MR imaging (ref. 16).
Adenoid-cystic carcinomas are rare,
malignant with propensity to perineural and vascular invasion and
affect younger patients. Adenocarcinoma and squamous cell carcinoma are
uncommon.
Lymphomas account for 10 % of all
orbital processes. Most of them are low grade MALT (mucosa-associated
lymphoid tissue) lymphomas and occur in middle aged patients with
systemic disease in about 70 % of cases. Lymphomatomas infiltration may
involve the superior extraconal part of the orbit, the lacrimal gland
(orbital and palpebral lobes), the retrobulbar space or appears as an
extension of sinonasal lymphomas. MR imaging shows typically homogenous
masses, molding the normal anatomic structures of the orbit (fig. 33).
Lacrimal involvement can mimic mixed tumor and in other locations
pseudotumors. According to Cytryn (ref. 17), specific signal intensity
of both lesions on MR imaging may provide useful indications :
lymphomas are hyperintense to fat on T2, brighter than on T1 weighted
images whereas pseudotumors, because of their fibrotic components
appear isointense on T2, darker than on T1 weighted images.
Orbital involvement occurs in
children with myelogenous leukemias and adults with chronic lymphatic
leukemias, may involve every tissue of the eye and orbit (fig. 34) and
is always part of a systemic disease (ref. 18). Apart from pseudotumors
other inflammatory processes often bilateral can involve the lacrimal
gland such as sarcoidosis, Wegener’s granulomatosis and
Sjögren’syndrome an autoimmune disorder with the sicca syndrome. | |
