Ocular choristoma with heterogeneous mesenchymal differentiation and concurrent anterior segment dysgenesis in a neonatal Holstein calf

Abstract

A 1-day-old Holstein calf presented with central corneal opacity and thickening, and a polypoid lesion in the medial canthus of the left eye, leading to vision loss and enucleation. Grossly, a mass extended from beneath the cornea to the medial intraocular region. Histologically, the mass was composed of proliferative foci of diverse mesenchymal elements, including mature cartilage and adipose tissue, immature cartilage and bone, and proliferating spindle-shaped cells in a myxoid stroma. Anterior segment abnormalities, including iris hypoplasia, iridocorneal adhesion, angle malformation, and lens anomalies, were also observed. The animal was diagnosed with an ocular choristoma with heterogeneous mesenchymal differentiation and anterior segment dysgenesis (ASD). To the best of our knowledge, this is the first report of choristoma with ASD in cattle.

Choristoma is a congenital, non-neoplastic lesion characterized by the ectopic histologically normal tissue [24]. In contrast, hamartoma is abnormal proliferations of tissue that are normally present at the affected site, and may include immature elements [13, 24]. However, the distinction between these entities has become less clear, and some authors have proposed that they should be understood as part of a continuous spectrum of developmental anomalies [16].

In veterinary medicine, ocular choristomas have generally been described according to the conventional concept of the disease. In cattle, dermoid choristomas (corneal dermoid) occurring in the cornea, conjunctiva, or third eyelid have been reported sporadically [2]. Intraocular choristomas are extremely rare, and are usually associated with congenital ocular malformations. In horses, cases involving bilateral ectopic lacrimal gland-like tissue and epithelial tissues that were suspected to be of ectodermal origin have been described [1, 15]. In white-tailed deer, intraocular choristomatous lesions associated with ocular maldevelopment and containing cutaneous adnexa and glandular structures have been reported [5], and in sheep ectopic dermoid tissue and glandular structures accompanied by cutaneous adnexa have been identified within the eye, including the iris and ciliary body [22].

Anterior segment dysgenesis (ASD) is a group of congenital disorders characterized by the maldevelopment of anterior ocular structures—including the cornea, iris, iridocorneal angle, and lens—resulting from impaired differentiation, migration, and/or maturation of neural crest-derived mesenchymal cells during embryogenesis [21]. In ASD, disruption of any of these developmental processes is considered to result in abnormalities, such as hypoplasia of the iris, ciliary body, or iridocorneal angle structures; malformation of the posterior cornea; or iridocorneal adhesion [21, 23]. In veterinary medicine, ASD-like anterior segment abnormalities have been reported in various animals, including cattle [8, 9, 17, 19].

Here, we report a neonatal calf presented with an ocular choristoma, which was characterized by the admixture of mature and immature mesenchymal tissue within the globe and conjunctival stroma, and concurrent ASD. To the best of our knowledge, no similar case has yet been described in the veterinary literature.

The case involved a 1-day-old female Holstein calf. Parturition occurred normally; however, immediately after birth thickening of the central cornea and opacity were observed in the left eye. In addition, a polypoid nodule, which was contiguous with the palpebral conjunctiva, was found to be protruding from the medial canthal region. Vision was absent from the left eye, and the globe was surgically enucleated. The specimen was submitted for histopathological examination.

The left eye was fixed in 10% neutral buffered formalin, sectioned along the horizontal midline, and examined grossly. For the histological examination, paraffin-embedded tissue sections were prepared according to standard procedures and stained with hematoxylin and eosin (HE). As a special stain, Alcian blue (AB, pH 2.5) staining was performed.

Immunohistochemical examinations were carried out using the immunoenzyme polymer method (Histofine Simple Stain MAX-PO; Nichirei, Tokyo, Japan). The following primary antibodies were used: mouse monoclonal antibodies specific for vimentin (V9; Dako, Glostrup, Denmark; prediluted), pan-cytokeratin (AE1/AE3; Nichirei; prediluted), α-smooth muscle actin (α-SMA; 1A4; Dako; 1:100), desmin (D9; Progen, Heidelberg, Germany; 1:80), and Ki-67 (MIB 1; Dako; 1:50). 3, 3′-diaminobenzidine was used as a chromogen, and the sections were counterstained with Mayer’s hematoxylin. Normal bovine skin tissue was used as a positive control during the detection of these antibodies.

On the cut-surface of the fixed left globe, a mass occupying the anterior intraocular region was observed immediately beneath the cornea, extending from the central cornea toward the intraocular side. In the corneoscleral limbal region, the mass was contiguous with another mass, which had formed along the sclerochoroidal space on the intraocular side and conformed to the curvature and structure of the globe (Fig. 1). In addition, in the corneoscleral limbal region a polypoid nodule, which protruded outward and was contiguous with the mass, was identified (Fig. 1). The intraocular mass was grossly divisible into three contiguous regions. The intraocular component, which was clearly demarcated and sclerochoroidal space, was white to partially grayish-white and exhibited a partially lobulated to solid architecture. The center of each proliferative focus contained a small, opaque to partially translucent nodule. This lesion was continuous with a solid tissue composed of two layers, which were grayish-white and white in color, respectively, and was adherent to the cornea. In the anterior segment of the central cornea, a more centrally located lesion was observed as a soft, gelatinous tissue mass composed of two different-colored layers, corresponding to a superficial glossy white layer and deeper white to partially graish-white components. The polypoid nodule arose contiguously from the outer margins of the anterior apex of the intraocular mass and contained centrally located, whitish, soft tissue.

Fig. 1.

Gross appearance of the cut surface of the fixed left globe. A mass is seen in the anterior chamber, extending from the central anterior segment immediately beneath the cornea and along the intraocular structures. The mass is composed of three grossly distinct regions: the central anterior segment immediately beneath the cornea (*); the anterior intraocular region, which is contiguous with and adherent to the cornea (**); and a well-demarcated region located between the choroid and sclera on the medial side (***). At the corneoscleral limbus, a polypoid nodule, which is contiguous with the outer margins of the anterior apex of the intraocular mass, is present (arrowhead). Bar=1.5 cm.

Histologically, the three grossly distinct regions of the intraocular mass showed different tissue components. The well-demarcated white to partially grayish-white mass located between the choroid and sclera was unencapsulated but relatively well demarcated. The mass was composed of lobular to multilobular proliferative foci of mesenchymal tissue of various sizes. These foci predominantly consisted of dense to loosely arranged myxomatous spindle-shaped cells. Within this background, areas of osteoid formation arranged in a trabecular pattern and immature to mature cartilaginous structures of varying size (from small island-like foci to larger confluent nodules), surrounded by varying degrees of spindle-shaped mesenchymal cells, were observed, with some peripheral adipose tissue (Fig. 2a–d). The grayish-white solid tissue adherent to the posterior aspect of the cornea was composed of a superficial myxomatous region of proliferating spindle-shaped cells accompanied by trabecular bone and a deeper proliferative focus, which was predominantly characterized by immature chondroid tissue (Supplementary Fig. 1a–c). The proliferating spindle-shaped mesenchymal cells had small, round to oval, slightly hyperchromatic nuclei, and no mitotic figures were observed (Fig. 2e). In contrast, the gelatinous tissue immediately beneath the central cornea consisted of loosely or densely arranged mesenchymal tissue rich in blood vessels (Supplementary Fig. 2a–c) and was contiguous with the region of the lens immediately beneath the cornea and with the stroma of the iris in a deeper region. The mesenchymal tissue was contiguous with the iris and ciliary body on the outer ocular side, and no apparent cellular atypia was observed in the constituent cells. The polypoid nodule was composed of mature cartilaginous tissue surrounded by several layers of spindle-shaped cells, located within the conjunctival stroma in close proximity to the intraocular mass. The lens was small, ellipsoid, with a thickened wavy capsule, degenerative lens substance, and posterior epithelial proliferation with fibrous metaplasia (Supplementary Fig. 3a). On the intraocular side corresponding to the mass, the iris and ciliary body were not observed, and the iridocorneal angle structures were absent due to the mass effect of the lesion. On the extraocular side, the iris was thin, and portions of the center of the iris were contiguous with the posterior corneal surface. At the iridocorneal angle, the scleral venous plexus was identifiable, but the trabecular meshwork was indistinct (Supplementary Fig. 3b). The retina overlying the mass and around the optic nerve head was extensively detached, and the associated retinal pigment epithelial cells were markedly swollen, exhibiting ballooning degeneration.

Fig. 2.

Histological images of the mesenchymal components observed in the part of the mass that form between the choroid and sclera on the medial side of the left eye. a: Myxomatous proliferation of mesenchymal cells with trabecular bone formation (HE, bar=200 µm); b: Islands of mature to immature cartilage of varying sizes (HE, bar=200 µm); c: Immature cartilaginous structures and the proliferation of spindle-shaped mesenchymal cells (HE, bar=100 µm); d: Formation of mature adipose tissue in the peripheral region of the lesion (HE, bar=100 µm); e: Histology of the proliferating mesenchymal cells forming the main component of the mass. Left: Spindle-shaped mesenchymal cells with small to medium, round to oval nuclei in densely proliferative areas (HE, Bar=20 µm); Right: Spindle-shaped cells with small, round, hyperchromatic nuclei in the myxomatous proliferative region (HE, bar=20 µm); f: Mucin production and accumulation in the stroma of the myxomatous proliferative region, which is positive for AB (AB, bar=100 µm).

AB staining demonstrated a blue-stained matrix in the cartilaginous tissue. In addition, the accumulation of blue-stained material were observed in the stroma of the myxomatous proliferative foci of spindle-shaped cells (Fig. 2f).

Immunohistochemically, the mesenchymal cellular components of the lesion, including the proliferating spindle-shaped mesenchymal cells, were diffusely positive for vimentin.No cytokeratin-positive cells were observed within the lesion. α-SMA and desmin immunoreactivity were detected in vascular structures, whereas the proliferating spindle-shaped mesenchymal cells were negative for both markers. In the mesenchymal cells constituting the mass, only a few Ki-67-positive nuclei were scattered, and the Ki-67 labeling index was 2.3%.

Based on the above findings, the mass was diagnosed as an ocular choristoma with heterogeneous mesenchymal differentiation, which was characterized by the formation of mature cartilage and adipose tissue in combination with immature mesenchymal components, and it was considered to be a non-neoplastic, ectopic lesion. In addition, congenital anomalies, predominantly affecting the anterior segment, were identified, including iris adhesion, iris hypoplasia, malformation of the iridocorneal angle, and a cataract associated with corneal adhesion (i.e., ASD). In the posterior segment, retinal detachment was diagnosed.

In humans, most reported intraocular or conjunctival choristomas consisted of mature mesenchymal or epithelial tissues, including bone, cartilage, adipose, and/or glandular tissue [10, 12]. In the present case, however, mature cartilage and adipose tissue were observed together with immature components, including mesenchymal cell proliferation, immature cartilage, and proliferating spindle-shaped cells within a myxoid stroma accompanied by immature trabecular bone formation. Although choristoma is classically defined as a congenital, non-neoplastic lesion composed of mature, fully differentiated tissues in an abnormal location [24], the immature components observed in the present case lacked cytological atypia, mitotic figures, and infiltrative growth, and are therefore considered to represent developmental immaturity rather than neoplastic proliferation. In addition, the low proliferative activity of the mesenchymal cells, as assessed by Ki-67 immunostaining, was consistent with the histological features suggesting a non-neoplastic lesion. The lesion extended from the intraocular region into the conjunctival stroma, and to the best of our knowledge, such a combination of findings has not been reported previously. Considering its congenital presentation, anatomical location, and morphological features, the lesion was interpreted as a developmental anomaly rather than a neoplasm such as low-grade mesenchymal neoplasms or myxoid tumors. Furthermore, teratoma was considered in the differential diagnosis; however, the absence of tissues derived from multiple germ layers supports exclusion of teratoma in the present case. Hamartoma was also considered as a differential diagnosis. However, because the present lesion comprised ectopic tissues that are not normally found at this site, it did not strictly match the definition of a hamartoma. Recently, it has been proposed that choristoma and hamartoma represent points along a “developmental anomaly spectrum” rather than distinct entities [16]. The coexistence of mature and immature mesenchymal components suggests incomplete mesenchymal differentiation during ocular development, although the exact developmental origin of these cells cannot be determined from the present findings.

In the current case, in addition to mass formation, developmental abnormalities of anterior segment structures were identified, leading to a diagnosis of ASD. ASD is a congenital disorders affecting the cornea, iris, ciliary body, iridocorneal angle, and lens, which is characterized by morphological and differentiation defects [21]. Ocular development depends on reciprocal interactions among the neuroectoderm-derived optic vesicle and cup, surface ectoderm-derived lens vesicle, and neural crest-derived mesenchyme. Anterior segment structures—including the corneal stroma and endothelium, iris, ciliary body, and trabecular meshwork—form through the stepwise migration, differentiation, and reorganization of neural crest cells [23, 25]. Disruption of these processes or inductive interactions with the optic cup may result in hypoplasia of the iris and/or ciliary body; disorganization of the iris stroma; iridocorneal angle dysgenesis; posterior corneal malformation; and, in some cases, iridocorneal adhesion [7, 21]. Abnormal development of the anterior segment can also affect the lens, whose invagination and differentiation depend on signals from the surrounding neural crest-derived mesenchyme. Mesenchymal abnormalities may therefore cause defective lens invagination, incomplete separation from the cornea, positional defects, and/or structural anomalies [6, 25]. In this case, fibrovascular tissue that was contiguous with the iris stroma was observed adjacent to the mass and the malformed lens. This tissue was distinct from the choristoma, and was interpreted as persistent embryonic mesenchymal tissue that failed to regress completely during anterior segment development. Its morphology was therefore considered consistent with a developmental abnormality associated with ASD [3, 18].

Although ASD is rare in cattle, sporadic cases have been reported. One of the earliest detailed case reports described a Holstein calf with congenital anterior staphyloma accompanied by a rudimentary lens [17]. This case exhibited unilateral central corneal opacity, exophthalmos, iris abnormalities, and absence of the lens, and was considered representative of the typical phenotype of ASD. Multiple congenital ocular malformations—including microphthalmos, microcornea, microlentia, retinal dysplasia and detachment, acorea, and ASD—were observed in a Brahman × Santa Gertrudis herd, suggesting the presence of hereditary ocular developmental abnormalities [9]. Furthermore, a case of developmental glaucoma associated with bilateral buphthalmia was reported in a 4-month-old Texas Longhorn bull [8]. In that case, dysgenesis of the trabecular meshwork and iridocorneal angle structures without evidence of inflammation was confirmed, indicating that developmental abnormalities associated with ASD may result in the malformation of anterior segment structures and secondary glaucoma. Finally, a Peters’-anomaly-like case of ASD was reported in a Holstein calf, which presented with unilateral exophthalmos, central corneal opacity, iridocorneal adhesion, and the absence of the lens, and pathological abnormalities, including defects of the posterior corneal layers and the absence of the corneal endothelium, was described [19]. In the present case, in addition to anterior segment abnormalities consistent with those described in previous reports, concurrent ocular choristomas were identified, which may reflect an additional developmental abnormality affecting ocular mesenchymal tissue. ASD accompanied by choristoma has not been reported previously in cattle, and the coexistence of these conditions represents a distinctive feature of the present case.

This report describes a neonatal calf with concurrent ocular choristomas with heterogeneous mesenchymal differentiation and ASD. ASD-associated ocular malformations coexisted with choristoma are extremely rare, with only two reports in horses [1, 15]. However, no previous reports have described a choristoma with both immature and mature mesenchymal tissue components seen in the present case. In humans, ocular choristomas such as limbal dermoids can be associated with anterior segment anomalies in conditions like Goldenhar syndrome and encephalocraniocutaneous lipomatosis, which involve abnormal development of neural crest- and neuroectoderm-derived tissues [4, 11, 14, 20]. In the present case, the coexistence of choristoma and ASD raises the possibility of a shared developmental background. Because both lesions are considered developmental abnormalities arising during morphogenesis, abnormal development of periocular mesenchyme, including neural crest-derived tissues, may have contributed to their concurrent occurrence. However, no direct evidence supporting this mechanism was obtained in the present case, and further studies are needed to clarify their possible developmental relationship.

Conflicts of Interest

The authors declared no conflicts of interest to the research, authorship, and/or publication of this paper.