Phakomatous Choristoma
Key Points
Phakomatous choristoma is a very rare congenital lesion
It is believed to arise early in the embryogenesis of the eye during the optic vesicle stage as tumor cells migrate toward the region of the embryonic choroidal fissure
Elements that eventually form the phakomatous choristoma may have been left behind in the mesenchymal tissue
Clinically, phakomatous choristoma presents as a smooth, firm, painless, generally immobile, palpable subcutaneous mass in the inferonasal eyelid
Surgical excision is the initial treatment of choice to rule out alternative diagnoses
The prognosis is excellent, and recurrences have not been reported
Phakomatous choristoma (PC), sometimes referred to as “Zimmerman tumor,” is a very rare congenital lesion, first described by Zimmerman in 1971.1 Since then fewer than 30 cases have been added to the literature.2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25
PC generally is present at birth, but in some cases, it may not become obvious until several weeks or months later.14,15,16,21,25 Although published cases are few, some studies reported a male predominance of about 2:1,14,25 whereas others report no apparent sex or ethnic predilection.16,22 The tumor occurs equally on the left and right sides, and all reported cases have been unilateral. Although phakomatous choristoma is usually an isolated abnormality, association with other congenital ocular abnormalities has been reported, including hypoplasia of the optic nerve and coloboma.20
Etiology and Pathogenesis
When first described, Zimmerman postulated a lenticular anlage origin for PC based on the similarity of the microscopic appearance of the epithelial components to cataractous lenses, the presence of a thick basement membrane, and the absence of mucin and sebum secretions.1 Since then, this histogenetic origin has been confirmed in several electron microscopic and immunohistochemical studies.4,6,7,8,10,11 It is thought that PC arises early in the embryogenesis of the eye during the optic vesicle stage as tumor cells migrate toward the region of the embryonic choroidal fissure.6
Because this tumor occurs primarily in the lower eyelid, Peres et al12 argued that PC must already have been present and growing at the time the eyelids are formed during embryogenesis. However, Seregaard14 noted that the lens is formed through a depression of the lens pit from the surface ectoderm between the 5- and 9-mm embryonic stages and that the lens vesicle remains connected to the surface by a thin stalk. After the disappearance of this stalk, the lens vesicle closes and is surrounded by the lens capsule.26 He argued that the elements that eventually form the phakomatous choristoma have to be left behind in the mesenchymal tissue before the 9-mm stage ends.14 Since the buds that eventually become the eyelids do not arise until after the 10-mm stage,27 and the bony walls of the orbit also develop after the 9-mm stage, deposition of the phakomatous elements that will form the tumor must occur before either the eyelid or orbit are anatomically defined. This supports the idea that these phakomatous elements are left behind in undifferentiated mesenchymal tissue that only later will give rise to the eyelids and orbit.
Several other hypotheses have been proposed for the origin of PC. These include aberrant migration of lenticular cells toward the embryonic choroidal fissure during the optic vesicle stage in early embryogenesis, invagination of surface ectoderm into the mesoderm of the eyelid, and proliferation of native ectodermal cells that are present in the subcutaneous tissue of the inferior medial eyelid.4,6,8,10,15,16,23
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
