Abstract
Diprosopia, a congenital defect process also known as craniofacial duplication, is well-recognized in humans and has also been reported in numerous animal species. Here we describe a case of diprosopia in a live mixed-breed beef calf. We used computed tomography imaging to characterize internal and external abnormalities which, to our knowledge, have not been reported in any diprosopic veterinary species. Additional diagnostic tools included postmortem examination and histopathology. This case highlights distinct anatomic features associated with diprosopia and underscores the unique challenges associated with classifying and managing fetal malformations.
Fetal malformation (colloquially termed “fetal monster”) broadly refers to the intrauterine development of one or more structural or functional anomalies. Some types of fetal malformations may be caused by conjoined twinning, which is classified based on symmetry, or lack thereof, and sites of union (Table 1). Symmetric twins are composed of equivalent individuals, whereas asymmetric twins are composed of a smaller individual (termed “parasite”) that is dependent on the larger individual (termed “autosite”). 4 Fetal twinning abnormalities involving the head are further classified as diprosopus, dicephalus, or janiceps/nonjaniceps.
Classification of conjoined twinning based on sites of union. 20
Diprosopia is the development of symmetric conjoined twins with a single head (i.e., shared skull) and duplication of one or more craniofacial structures (e.g., eyes, ears, maxillae, mandibles; Fig. 1). Five distinct types of diprosopus have been described in veterinary species (Table 2). 13 Types 1–4 most likely represent diprosopus, whereas type 5 could indicate diprosopus or dicephalus, a grossly similar but separate condition defined as conjoined twins with 2 completely separated heads (including separate skulls and brains). Dicephalus can be further categorized as iniodymus (2 skulls with fusion at the occipital region), atlodymus (2 skulls, 1 neck), or derodymus (2 skulls, 2 necks). Another grossly similar condition is janiceps because this type of fetal malformation also has 2 faces similar to diprosopus. However, janiceps is a type of cephalopagia that includes 2 faces, whereas diprosopus is a form of parapagia. Nonjaniceps is a rarer form of cephalopagia that has a single head and face.25,38,40 We describe here in a live mixed-breed beef calf a unique case of diprosopia, which was characterized by computed tomography (CT) with contrast, postmortem examination, and histopathology.
Artistic rendering demonstrating examples of facial duplication in diprosopic calves (adapted from reference 5).
Classification of craniofacial duplications. 13
Materials and methods
A 3-d-old female mixed-breed beef calf born on 2020 June 21 was donated to Mississippi State University for teaching purposes after the owner noticed several striking anatomic deformities. The 2–3-y-old mixed-breed beef dam of the calf had been purchased as a yearling and had raised one healthy calf previously. In the case of the affected calf, the dam was bred to a registered Limousin-Angus hybrid herd bull. No previous history of congenital defects or poor reproductive performance was reported in the herd. The referring veterinarian noted that the pasture did not contain any known toxic plants. The owner and referring veterinarian administered calf starter (Ampli-Calf starter; Purina) via orogastric tube because the calf was unable to nurse.
Upon presentation to Mississippi State University Animal Health Center (MSU-AHC), the calf received a physical examination and was immediately given milk replacer (~284 mL; Land O’Lakes) via orogastric tube. The next day, full-body CT imaging with contrast was performed to assess the extent of internal and external anatomic abnormalities. The calf was sedated using intravenous xylazine (0.1 mg/kg) and ketamine (5 mg/kg), and was positioned in sternal recumbency on a CT scanner (Aquillion16-slice; Toshiba). Images were acquired in the transverse plane in bone and soft tissue kernels and reconstructed as needed for optimal viewing. An initial scan was performed, followed by scans at 20 and 90 s after intravenous administration of 60 mL of ioversol (Optiray 320; Guerbet). The attending clinicians elected to euthanize the calf given a poor prognosis.
A postmortem examination was performed following euthanasia. Samples of all major organs were collected and placed in 10% neutral-buffered formalin for histologic examination. Additionally, an ear notch was submitted for bovine viral diarrhea virus (BVDV; Pestivirus) real-time PCR. Routine histopathology was performed on formalin-fixed lung, liver, kidneys, spleen, heart, skin, cerebellum, brainstem, and globes. To preserve the skull, histologic examination of the CNS tissues was restricted to selective sections of the cerebellum and brainstem retrieved through the foramen magnum. The skull was left intact for use as a teaching specimen and was processed using gross dissection, defleshing using a dermestid beetle colony, and 3% hydrogen peroxide. After processing, the skull was reconstructed using CT images for reference.
Animal case reports published prior to 2020 September 18 were obtained, and only papers available in English were considered. PubMed and the Mississippi State University Library system (http://library.msstate.edu/) were searched using the terms “diprosopus,” “diprosopia,” and “conjoined twin craniofacial duplication.” The terms “janiceps” and “dicephalus” were also included to address misdiagnoses in some papers. From this search, we retrieved no cases of diprosopia with accompanying CT imaging, suggesting that no descriptions of this condition with imaging have been reported in veterinary species.
Results
Physical, neurologic, and ophthalmic examinations
On physical examination, the calf’s body temperature, pulse, and respiration were 38.3°C, 124 bpm, and 56 respirations per minute, respectively. The calf had a body condition score of 2 of 9 and weighed 28.1 kg. The mucous membranes were pink and moist.
Several striking external deformities were noted (Fig. 2). The oral cavity was composed of 2 partial maxillae, each with 2 patent nares and left and right dental arcades, respectively; 1 functional tongue; and 1 shared mandible. Between the 2 partial maxillae, there was a 4.8-cm shared palatoschisis defect. Rostral to this defect and protruding from the oral cavity was a 4 × 2.7 × 2.7-cm globe with associated eyelashes. A thick, white-tan membrane covered the cornea of the central globe, indicating a corneal ulcer. The right and left globes were positioned appropriately, with mild entropion. Anatomically normal ears were located appropriately on the right and left regions of the head. A 7 × 5-cm flap of haired skin was present in the center of the forehead and extended downward to cover the opening of the oral cavity. This tissue was not cystic and did not communicate with underlying structures. An open fontanel was palpated dorsal to this skin abnormality. Heart and lung sounds auscultated normally, and no joint swelling was appreciated upon manipulation and palpation. The remainder of the physical examination was within normal limits.
A complete neurologic examination could not be performed given the calf’s instability when standing or walking, which was attributed to her disproportionately heavy head. Assessment of the cranial nerves revealed intact pupillary light, menace, and palpebral responses in the right and left globes. Horizontal nystagmus was present in the right and left globes, but no directional phase was documented. The jaw and tongue had good tone. The calf could suckle, and when tube fed was able to move ingesta through the gastrointestinal tract. Superficial and deep pain as well as conscious proprioception were present. Spinal reflexes were also intact. These findings suggest intact optic, oculomotor, mandibular branch of the trigeminal, facial, and glossopharyngeal nerves. Deficits were identified in the trochlear, abducens, and vestibulocochlear nerves. The olfactory nerve, and maxillary and ophthalmic branches of the trigeminal, were not assessed. Additionally, the vagus, accessory, and hypoglossal nerves could not be assessed accurately because of the large cleft palate.
Imaging
CT imaging confirmed many of the physical examination findings, with additional features of notable interest (Fig. 3). Most of the osseous duplication was present from the level of the optic chiasm rostrally, with anomalous sphenoid and basisphenoid bones. The frontal bones were asymmetric and misshapen. A large open fontanel was present on the left at the base of the grossly identified skin abnormality between the presumed left frontal and left parietal bones. The right and left globes had normal optic nerves that coursed medially to an individual optic canal. The central ocular structure had 2 optic nerves that coursed caudally to an enlarged single, centrally located optic canal. The central ocular structure was ovoid, with a thin septum down the center dividing the structure into left and right portions, each with an individual lens. The tympanic bullae were filled with fluid-attenuating material bilaterally.
Computed tomographic images of a diprosopic calf head.
Numerous portions of the cerebrum were absent or unrecognizable. Along the left and right lateral aspects of the calvaria, portions of brain parenchyma resembled cortex. Medial to the presumed cortex were large, irregularly shaped, fluid-filled regions that resembled malformed lateral ventricles. In addition to the presumed lateral ventricles, a presumed malformed third ventricle was also dilated and irregularly shaped with irregular communications. A normal thalamus was not identified. Within the fluid-filled regions of the central aspect of the brain, there were 3 variably sized and irregular soft tissue–attenuating islands of brain parenchyma. Along the left lateral aspect of the cerebrum, cortical tissue was absent. Loss of communication of the presumed anomalous left lateral ventricle to the meninges was also noted. On the midline, the basisphenoid bone contained a depression resembling the sella turcica, within which was an ovoid structure. This structure, which was hyperattenuating to the remaining brain parenchyma, was interpreted as a single pituitary gland. With contrast, the vasculature of the cerebrum was also anomalous, which hindered accurate identification. The cerebellum appeared normal.
The thorax, abdomen, and extremities were evaluated for concurrent congenital defects, but none was identified.
Postmortem examination
Real-time PCR testing for BVDV was negative. The central ocular structure was composed of 2 fused globes within a single orbit, each with its own optic nerve (Fig. 2). This structure had a nictitating membrane but lacked upper and lower eyelids. The cornea was diffusely cloudy. Each globe had separate lenses and separate posterior segment structures including its own vitreous chamber, choroid, retina, and optic nerve. The fused globes shared a common iris, anterior chamber, and cornea. In addition to the central ocular structure, grossly normal right and left globes were present in anatomically appropriate locations on either side of the face. Upon disarticulation of the head, ~0.6 L of CSF drained from the spinal canal. Following defleshing of the skull, the extent of skull deformities could be appreciated, including an open 4.5 × 6.7-cm fontanel, a 7.4-cm wide cleft palate, duplicated and laterally rotated partial maxillae, and anomalous loose bony fragments that we could not reassemble into their appropriate anatomical locations using CT for reference (Fig. 4).
Reconstructed skull of diprosopic calf.
Histopathology
One examined section of lung from the right caudal lobe had suppurative bronchopneumonia with intralesional hypereosinophilic globular material, consistent with pneumonia caused by aspiration of milk replacer. Additional sections of lung, liver, kidneys, spleen, heart, skin, cerebellum, and brainstem were within normal limits.
The central ocular structure contained 2 partially fused globes, each of which contained a lens and normal posterior segment structures, including vitreous fluid, choroid, retina, and optic nerve. The sclera was partially complete, with the exception of where the globes were fused to form a common central fused iris and ciliary body (Fig. 5). The fused globes shared a common cornea and anterior chamber. The cornea was diffusely ulcerated with intralesional mixed bacteria, with cocci predominating. The peripheral corneal stroma contained abundant neutrophils, fibrin, and small proliferative vessels. The anterior chamber also contained neutrophils and fibrin. There was moderate degeneration of the cortical lens.
Subgross image of the central ocular structure composed of 2 medially fused globes with separate lenses; separate posterior segment structures (vitreous chamber, choroid, retina, optic nerves); and a common iris, anterior chamber, and cornea. Retinal detachment and lens fragmentation are artifactual. H&E.
At the time of diagnosis, the eye was characterized with synophthalmia, exposure keratopathy with focally extensive full-thickness corneal necrosis, mild neutrophilic endophthalmitis (hypopyon), and a cortical cataract; however, based on the literature, we instead classify the eyes as tetrophthalmic. 40 Based on the combination of craniofacial defects and ocular anomalies, we classified this case as a symmetric parapagus diprosopus tetrophthalmos calf.
Discussion
To our knowledge and further to our literature search, diprosopia has not been reported previously in any veterinary species to include CT diagnostic imaging, which provides detailed characterization of the skeletal abnormalities associated with this condition. Investigation of diprosopia is diagnostically and clinically relevant, given that this condition has been reported in a variety of mammalian, avian, and bony and cartilaginous fish species (Table 3). Interestingly, cattle are the animal species reported most frequently with fetal malformation, despite being less likely to produce twins than sheep and goats, which have fewer reports of fetal malformation. Although all diprosopic animals begin as monozygotic conjoined twins, the pathogenesis of diprosopia is not fully understood.
Summary of published diprosopus cases in animal species.
F = female; M = male; NR = not reported; PS = pseudohermaphrodite.
Three main hypotheses of diprosopia development have been proposed in the human literature, including fusion (Spencer hypothesis), fission (Carles hypothesis), and duplication (Bidondo hypothesis). 5 In the Spencer hypothesis, the embryo completely separates appropriately into 2 individuals, which then rejoin and may result in multiple abnormalities; the 2 embryonic discs move around one another as if on the surface of a sphere and eventually collide to fuse at sites of compromised ectoderm. The Carles hypothesis proposes incomplete fission (i.e., splitting) of the embryo during the primitive streak stage. The Bidondo hypothesis postulates that duplication of the early primitive node drives right and left polarity; in response to this nodal alteration, diverging signals occur at the midline and tissues duplicate to assume a random right or left laterality. 5
Inciting factors for the development of diprosopia have not been identified; however, proposed causes include viral infection, toxic plant ingestion, one or more vitamin deficiencies, environmental variables, and genetic influences. Diprosopia has no known association with maternal age, parity, fetal developmental stage, hereditary, or environmental influences. Although there is no reported sex predisposition in veterinary species, human cases are reported more frequently in females than males, and available reports in bovids show a female:male sex ratio of 18:11 (Table 3). 5
Diprosopia may be accompanied by other congenital defects, notably cardiac and limb anomalies; however, we did not note any such defects in our calf. Although this calf was born naturally with no observed complications during parturition, dams with diprosopic pregnancies often experience dystocia and are unable to pass the malformed fetus, requiring either assisted delivery or Cesarean section.1,3,6,8,28,35,37,42,43,45
Historically, discrepancies in the terminology used for classifying craniofacial duplication as diprosopus or dicephalus have potentially led to mischaracterization of these conditions.3,12,15,18,21,34,35,37,39,44,46 We recommend that the term 2 heads be avoided because this suggests dicephalia. Instead, descriptive terms for diprosopia can include craniofacial duplication or 2 fused faces or heads, which highlights the twin origin, to eliminate reader confusion.
Another point of discussion is the term synophthalmia. In our review of the literature, only one paper used this term to describe the fusion of 2 globes. 31 Human literature reserves the use of synophthalmia for cyclopic individuals, with the medical dictionary defining synophthalmia as “a congenital defect in which the 2 orbits are united to form a single cavity containing 1 eye, which typically results from union of the right and left optic primordia, usually combined with holoprosencephaly or cyclencephaly” (Farlex Partner Medical Dictionary, https://medical-dictionary.thefreedictionary.com/synophthalmia). We propose that synophthalmia be reserved for cyclopic individuals only. This is an important distinction because cyclopia arises in one individual, whereas diprosopia arises within conjoined twins. Instead, triophthalmos or tetrophthalmos should be used for diprosopic individuals. We classified our case presented here as tetrophthalmic given the presence of 2 partially fused globes in addition to 2 normal globes.
We diagnosed our case as symmetric parapagus diprosopus tetrophthalmos as defined in the current literature. 40 Additionally, based on the categorization of diprosopus into 5 types, 13 our case signifies a distinct variant involving 4 eyes, 2 ears, 1 mandible, 1 cerebrum, 1 cerebellum, and 1 pituitary gland. Our neurologic examination supports the findings of cerebral and/or cerebellar disease without spinal involvement. The use of CT imaging in our case also confirmed this finding and allowed for highly detailed, antemortem visualization of skeletal and soft tissue malformations. The addition of highly sensitive imaging techniques can provide insight into prognosis and potential management strategies for similar cases in veterinary medicine.
Footnotes
Acknowledgements
We are grateful to the owner who donated this calf, the referring veterinarian (Dr. Lowell Rogers), the county agent (Dr. Brad Jones) for providing emergency care, and the Mississippi State University Food Animal veterinarian (Dr. Gretchen Grissett) for providing in-hospital care. The Mississippi State University College of Veterinary Medicine generously donated teaching funds to pay for the imaging and care of this animal. We are extremely grateful to Dr. Teixeira Leandro of the Comparative Ocular Pathology Laboratory of Wisconsin at the University of Wisconsin–Madison who provided ophthalmic consultation, to Kiersten Combs for creating medical illustrations of fetal anomalies, and to Dr. Natalie Stilwell for her extensive assistance on final revisions for this manuscript.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
