Pure lymphatic malformations (LMs; previously called lymphangiomas) are low-flow orbital lesions resulting from disruption of the initially pluripotent vascular anlage, which leads to aberrant development and congenital malformation. LMs can also occur in the conjunctiva (Fig 5-2A), eyelids, oropharynx (Fig 5-2B), or sinuses. In the orbit, LMs usually become apparent in the first or second decade of life. They can be described as macrocystic (cysts ≥2 cm), microcystic (cysts ≤2 cm), or mixed macrocystic/microcystic. LMs cannot be decompressed and do not distend with a Valsalva maneuver. However, they may enlarge during upper respiratory tract infections, and they may present with sudden proptosis caused by spontaneous intralesional hemorrhage (chocolate cysts).
Figure 5-2 Lymphatic malformation. A, External photograph shows lymphatic malformation presenting as a hemorrhagic subconjunctival mass. B, Involvement of the hard palate (arrow). C, T2-weighted axial MRI shows multiple saccular lesions with serum and blood fluid levels (arrow) medial to the optic nerve. D, External photograph after injection with bleomycin.
(Courtesy of Bobby S. Korn, MD, PhD.)
The natural history of LMs is variable; some are localized and progress slowly, whereas others may diffusely infiltrate orbital structures and enlarge inexorably. MRI may show pathognomonic features (multiple grapelike cystic lesions with fluid–fluid layering of serum and red blood cells), confirming the diagnosis (Fig 5-2C).
LMs are characterized by their hemodynamic properties, and classification schemes continue to evolve. Some LMs possess a significant venous flow component and have clinical characteristics that overlap with venous malformations (VMs, discussed later in this chapter); these lesions are termed combined lymphatic venous malformations. Treatment depends on the hemodynamic flow characteristics of the lesion.
Histologically, pure LMs are characterized by serum-filled channels lined by flat endothelial cells that have immunostaining patterns consistent with lymphatic capillaries. Scattered follicles of lymphoid tissues are found in the interstitium. These lesions have an infiltrative pattern and are not encapsulated.
Treatment of LM is challenging for several reasons: the vascular channels are typically not amenable to endovascular approaches, the infiltrative nature of the lesion often involves vital orbital structures, significant hemorrhage may occur during surgery, and recurrence is common. Observation is a reasonable approach for lesions that are asymptomatic and not amblyogenic. If treatment is warranted, debulking of the lesion combined with use of intralesional sclerosing agents, either percutaneous or intraoperatively, may be successful. Sclerosants include morrhuate sodium, bleomycin (Fig 5-2D), polidocanol, OK-432, thrombosing agents such as fibrin glue, and embolizing agents such as cyanoacrylate glues and ethylene vinyl alcohol copolymer.
Acute hemorrhage complicated by optic neuropathy or corneal ulceration may respond to ultrasound-guided aspiration of blood through a hollow-bore needle or by open surgical exploration. While mild hematomas may resolve spontaneously, the mass effect of such hemorrhages can persist due to bleeding within dead-end lymphatic channels.
Noncontiguous intracranial vascular malformations have been reported to occur in up to 25% of patients with orbital LMs. These lesions have a low rate of spontaneous hemorrhage and are not treated prophylactically.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.