Background
Bregmatic sutural bone is an anatomical deviant of the skull that is associated with deficient closure of the suture at the bregma [1]. Despite the unusualness of sutural bone also known as wormian bone, intrasutural bone, or supernumerary bones, studies have reported its presence in humans and animals in different locations of the skull (along corona suture, at lambda, along lambdoid suture, epipteric, and bregma) [2-6]. Whereas, there is a paucity of reports on the occurrence of sutural bone at the bregma. Hence this report displays a rare case of the occurrence of sutural bone at the bregma referred to as bregmatic sutural bone.
The human cranium is important and complex; this could be ascribed to its relationship with the nervous system as it contains tissues like the encephalon, organs of vision, smell, and inner ear. It also supports the external organs of digestion and respiratory apparatus, and plays a role in direction of human movement [2,7]. The physiological impacts of sutural bones are not fully elucidated, but studies have reported it as an ethnic variable of interest to human anatomy, physical anthropology, forensic medicine, and radiology [6,8,9]. Sutural bone could form the basis for the anatomical variations observed in the skull and its center of ossifications; thus, this report could reveal and support the possibility of variations in ossification centers and skull matrix.
Case Presentation
During the maceration practical class by year 3 anatomy students, a male skull with a sutural bone located at the bregma was discovered. This unusual bregmatic sutural bone was interposed at the junction between the coronal and sagittal sutures of the cranium (Figure 1A). The bone was large, oval-shaped, and had a dimension of 50.3 × 40.4 mm when measured with a digital vernier caliper. A small sutural bone with a dimension of 10.6 × 10.4 mm was also observed along the left half of the lambdoid suture on the same skull (Figure 1B). This unique case was discovered in the Department of Anatomy of the College of Medicine and Health Sciences, Gregory University Uturu, Abia State, Nigeria.
Discussion
This report presents the first reported incidence of human bregmatic sutural bone in Nigeria and Africa as well as one of the rare, reported cases across the globe. Studies have reported the presence of sutural bones at different parts of the skull; the most common being found around the lambdoid suture followed by the epipteric bone found near the former anterolateral fontanelle, others include preinterparietal bone or Inca bone at the lambda and sutural bone along the corona suture [6,10]. Bregmatic sutural bone is very rare; the first reported case of human bregmatic sutural bone was in Asia (India) [2]. Since then, there are few reports on it across the globe [3,5]. The first animal (Lizard) reported case of bregmatic sutural bone in Africa was in 2018 [11]. Although, most of the reported cases display the location of sutural bones in the neurocranium; there are also a few cases reported on the viscerocranium (orbit, frontonasal suture) [4,12,13].
Showing various sutural bones in the skull; (A) bregmatic sutural bone, (B) sutural bone along lambdoid suture.
Bregma is the location in the skull where sagittal and coronal sutures meet; it is represented by the anterior median fontanelle in the fetal life which obliterates by the 18th postnatal month. The presence of the bregmatic sutural bone was suggested to be a result of an abnormal ossification center in the fibrous membrane at the anterior median fontanelle [2,14]. Bregma is an essential clinical and surgical landmark, so it was proposed that the bregmatic sutural bone be called median frontoparietal sutural bone [2]. Bregmatic sutural bone could be misdiagnosed for skull fractures; hence this reported anatomical variation present at the bregma of the skull forms knowledge that may be of importance to radiologists, orthopedic surgeons, neurosurgeons, and other related professions in their diagnoses and practices.
Conclusion
This report displays the first reported case of human bregmatic sutural bone (sutural bone at bregma of the skull) in Nigeria, Africa, and one of the few reported cases across continents of the globe. This supports the possibility of variations in ossification centers and skull matrix; hence, provides knowledge that can aid neurosurgeons, orthopedics, radiologist, anatomists, and other medical/health professionals in their diagnoses and practices.
What is new?
The human bregmatic sutural bone is an unusual variation of the human skull that can be misdiagnosed as a skull fracture. The knowledge of this case report reveals and supports the possibility of this anatomical variation, which is of vitality to neurosurgeons, orthopedics, anatomist, anthropologists, and forensic medical professionals in their diagnoses and practices. Although only a few cases have been reported across the continent about the human bregmatic sutural bone. This is the first reported case in Africa.