Fetal head anomaly restricted to the eye, the mandible, and the pterygoid process of the sphenoid: A histological study

Association between the developing sphenoid and adult morphology: A study using sagittal sections of the skull base from human embryos and fetuses

The developing sphenoid is regarded as a median cartilage mass (basisphenoid [BS]) with three cartilaginous processes (orbitosphenoid [OS], ala temporalis [AT], and alar process [AP]). The relationships of this initial configuration with the adult morphology are difficult to determine because of extensive membranous ossification along the cartilaginous elements. The purpose of this study was therefore to evaluate the anatomical connections between each element of the fetal sphenoid and adult morphology. Sagittal sections from 25 embryos and fetuses of gestational age 6-34 weeks and crown-rump length 12-295 mm were therefore examined and compared with horizontal and frontal sections from the other 25 late-term fetuses (217-340 mm). The OS was identified as a set of three mutually attached cartilage bars in early fetuses. At all stages, the OS-post was continuous with the anterolateral part of the BS. The BS included the notochord and Rathke's pouch remnant in embryos and early fetuses. The dorsum sellae was absent from embryos, but it protruded from the BS in early fetuses before a fossa for the hypophysis became evident. Although not higher than the hypophysis at midterm, the dorsum sellae elongated superiorly after gestational age 25 weeks. In early fetuses, the AP was located on the side immediately anterior to the otic capsule. The AT developed on the side immediately posterior to the extraocular rectus muscles. At late term, the greater wing was formed by membranous bones from the AT and AP. The AT and AP formed a complex bridge between the BS and the greater wing. A small cartilage, future medial pterygoid process (PTmed) was located inferior to the AT in early fetuses. At midterm, one endochondral bone and multiple membranous bones formed the PTmed. The lateral pterygoid process (PTlat) was formed by a single membranous bone plate. Therefore, we connected fetal elements and the adult morphology as follows. (1) Derivative of the OS makes not only the lesser wing but also the anterior margin of the body of the sphenoid. (2) Derivatives of the BS are the body of the sphenoid including the sella turcica and the dorsum sellae. (3) Most of the greater wing including the foramen rotundum and the foramen oval originate from the AT and AP and multiple membranous bones. (4) The PTmed originate from endochondral bones and multiple membranous bones, while the PTlat derive from a single membranous bone.

The palatomaxillary suture revisited: A histological and immunohistochemical study using human fetuses

In human fetuses, the palatine process of the maxilla is attached to the inferior aspect of the horizontal plate of the palatine bone (HPPB). The fetal palatomaxillary suture is so long that it extends along the anteroposterior axis rather than along the transverse axis. The double layered bony palate disappears in childhood and the transverse suture is formed. To better understand the development of the double layered bone palate, we examined histological sections obtained from 25 fetuses of gestational age 9-11, 16-18 and 30 weeks. The double layered palate was seen in all of the specimens examined. Inferior angulation of the posterior end of the HPPB was evident at 9-11 weeks, but the initial palatine aponeurosis did not attach to the angulation but to a slightly anterior site. Both the maxilla and the HPPB were tightly attached to the vomer at 16-18 weeks. In both bones, bilateral plates met at the midline. The palatomaxillary suture was filled with short, randomly arranged collagen fibers. The nasal end of the suture was covered by a tight periosteum. Immunohistochemical examination of 3 fetuses at 16-18 weeks showed: 1) no expression of versican, tenascin-c or type II collagen in the suture; 2) few mitotic cells positive for proliferating cell nuclear antigen; 3) no or few CD34-positive developing vessels; and 4) no CD68-positive macrophages. These findings suggested that the fetal palatomaxillary suture was inactive for reconstruction and growth and that soft palate muscles likely did not contribute to the development of the double layered configuration.

Neuronal differentiation in the early human retinogenesis

AIM

Our study investigates the differentiation of retinal stem cells towards different neuronal subtypes during the critical period of human eye development.

METHODS

Expression of the neuronal marker neurofilament 200 (NF200), tyrosine hydroxilase (TH) and choline acetyltransferase (ChAT) was seen by immunofluorescence in the 5th-12th - week stage of development in the human eye. Data was analysed by Mann-Whitney, Kruskal-Wallis and Dunn's post hoc tests.

RESULTS

NF200, TH and ChAT cells appeared in the 5th/6th week and gradually increased during further development. The proportion of TH positive areas were distributed similarly to NF200, with a higher proportion in the outer neuroblastic layer. The proportion of a ChAT positive surface was highest in the 5th/6th - week whilst from the 7th week onwards, its proportion became higher in the optic nerve and inner neuroblastic layers than in the outer layer, where a decrease of ChAT positive areas were seen.

CONCLUSIONS

Our study indicates a high differentiation potential of early retinal cells, which decreased with the advancement of development. The observed great variety of retinal phenotypic expressions results from a large scale of influences, taking place at different developmental stages.

The anatomy of fetal peripheral lymphatic vessels in the head-and-neck region: an immunohistochemical study

Using D2-40 immunohistochemistry, we assessed the distribution of peripheral lymphatic vessels (LVs) in the head-and-neck region of four midterm fetuses without nuchal edema, two of 10 weeks and two of 15 weeks' gestation. We observed abundant LVs in the subcutaneous layer, especially in and along the facial muscles. In the occipital region, only a few LVs were identified perforating the back muscles. The parotid and thyroid glands were surrounded by LVs, but the sublingual and submandibular glands were not. The numbers of submucosal LVs increased from 10 to 15 weeks' gestation in all of the nasal, oral, pharyngeal, and laryngeal cavities, but not in the palate. The laryngeal submucosa had an extremely high density of LVs. In contrast, we found few LVs along bone and cartilage except for those of the mandible as well as along the pharyngotympanic tube, middle ear, tooth germ, and the cranial nerves and ganglia. Some of these results suggested that cerebrospinal fluid outflow to the head LVs commences after 15 weeks' gestation. The subcutaneous LVs of the head appear to grow from the neck side, whereas initial submucosal LVs likely develop in situ because no communication was evident with other sites during early developmental stages. In addition, CD68-positive macrophages did not accompany the developing LVs.