mercoledì 13 ottobre 2010
Intraorbital Lymphatic Malformation
Figure 1: There is a multilobulated mass lesion in the retroorbital region with a fluid- fluid level.
Figure 3: There is an intraconal multilobulated mass with a fluid-fluid level and mild right globe proptosis.
Diagnosis: Intraorbital Lymphatic Malformation
Vascular lesions account for 5-20% of all orbital masses, and the two most common orbital vascular lesions are venous malformations (formerly known as cavernous hemangiomas) and lymphatic malformations (LM) ( formerly known as lymphangiomas). LMs are relatively uncommon in the pediatric population and account for only 4% of all childhood orbital masses. LMs are benign and most frequently found in the head and neck. Intraorbital LMs can arise in any orbital space, but are most commonly intraconal with frequent extraconal and preseptal expansion. Histologically, a vascular malformation can contain venous and lymphatic components, hence the name lymphaticovenous malformation. Of note, 70% of orbital lymphaticovenous malformations are associated with ipsilateral, noncontiguous, intracranial vascular abnormalities.
Intraorbital venous-lymphatic malformations are present at birth, but tend not to be discovered clinically until early childhood when they enlarge as a result of either intralesional hemorrhage or lymphoid hyperplasia and result in acute proptosis. Approximately one-half of all patients with orbital LMs also complain of limited ocular mobility. Additionally, conjunctival, facial, or oral vesicles may also be observed.
Radiologic imaging of intraorbital LMs demonstrates unencapsulated, irregular, lobulated, and multicompartmental masses. These lesions can have cystic as well as more solid components. The cystic elements of these masses commonly exhibit fluid-fluid levels as a result of intralesional hemorrhage. Additionally, LMs are frequently both pre- and postseptal and intra- and extraconal. They often display orbital expansion with irregular margins that traverse tissue planes. Ultrasound images of LMs demonstrate heterogeneous, ill-defined lesions with anechoic cystic portions and extraconal extension. On CT, these masses exhibit ill-defined borders, irregular attenuations, and variable enhancement with peripheral rim enhancement in cystic regions. Additionally, calcified phleboliths can be seen on CT in venous portions of these lesions. MR imaging is the preferred imaging modality to evaluate the location, vascular components and evolving blood products of venous-lymphatic malformations. LMs demonstrate iso- to slightly high signal intensities on T1-weighted images and very high signal intensities on T2-weighted images. MR imaging also allows for the simultaneous evaluation of the brain in an effort to detect any associated intracranial vascular anomalies.
The differential diagnosis for pediatric orbital tumors can be divided into osseous and non-osseous lesions. Pediatric osseous lesions of the orbit include dermoid inclusion cysts, which are most common, fibrous dysplasia, juvenile ossifying fibroma, osteosarcoma, Langerhans cell histocytosis, granulocytic sarcoma and neuroblastoma bone metastases. Non-osseous lesions of the pediatric orbit include most commonly rhabdomyosarcoma, but additionally infantile fibromatosis, infantile hemangioma, and LM.
Orbital lymphaticovenous malformations are histologically benign, but can demonstrate aggressive behavior, such as vision loss, as they expand. The treatment of such lesions is focused on ameliorating pain, alleviating optic nerve compression, maintaining ocular alignment and improving cosmetic appearance. Surgical resection is the preferred treatment for these lesions, and while complete removal can often be achieved with well-demarcated extraconal lesions, more diffuse intraconal lesions tend to be treated with subtotal resection.