|Year : 2021 | Volume
| Issue : 3 | Page : 174-177
Accessory nutrient foramen in the mandibular ramus
Haley L Nation1, Kevin P Adams2, Chinonye C Agu-Udemba2
1 Additional Professor, Department of Cell Systems and Anatomy, University of Texas Health Science Center at San Antonio, TX, USA
2 Additional Professor, School of Dentistry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr. San Antonio, TX, USA
|Date of Submission||08-Feb-2021|
|Date of Decision||07-May-2021|
|Date of Acceptance||15-Jun-2021|
|Date of Web Publication||30-Jul-2021|
Haley L Nation
Department of Cell Systems and Anatomy, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr. San Antonio, TX 78229
Source of Support: None, Conflict of Interest: None
While numerous anatomical variations in the osteology of the mandible have been reported, the current case describes a unique nutrient foramen in terms of its location and function. During an anatomical dissection of the infratemporal fossa, an accessory nutrient foramen was found in the mandibular ramus of a 93-year-old male dentulous cadaver. An anomalous vein draining the masseter muscle traversed the foramen. This venous structure was traced into a nutrient canal located anterior to the mandibular canal. To our knowledge, the location and function of the accessory nutrient foramen and anomalous vein have never been previously reported. These unique characteristics make this accessory nutrient foramen clinically relevant. Knowledge of accessory foramen in the mandibular ramus and similar anatomical variations may reduce the risk of injury to traversing structures during numerous surgical procedures.
Keywords: Accessory nutrient foramen, masseter muscle, nutrient foramen
|How to cite this article:|
Nation HL, Adams KP, Agu-Udemba CC. Accessory nutrient foramen in the mandibular ramus. Natl J Clin Anat 2021;10:174-7
| Introduction|| |
Many variations in the mandible osteology have been previously reported including accessory mandibular foramen, retromolar foramen, accessory mental foramen, and nutrient foramen. Injury to the structures traversing such variants may lead to hemorrhage and paresthesia; therefore, knowledge of these variants and reportage of novel, undescribed, cases is important to prevent such complications.
This anatomical case study does not fit the description of any variant described in the current body of literature. Numerous radiology publications have revealed duplication of the mandibular canal which commence at an accessory mandibular foramen., Publications have demonstrated the presence of bifid mandibular canals; the single mandibular canal contains an offshoot that encases large branches of the inferior alveolar nerve. Previous literature has also described retromolar canals which have been defined as a bony channel extending from the mandibular canal and terminating as a retromolar foramen, posterior to the third molar in the retromolar fossa., Accessory mental foramen is described as an additional, smaller, foramen located near the mental foramen, and are continuous with the mandibular canal. Due to their specifically defined locations and defined traversing contents, the current case study does not represent these variations.
The variation that best describes the current case report is a modified nutrient foramen. Although the definition is controversial, nutrient canals have been described as paradental or interdental channels that function to bring nutrition to the region by ways of interdental arteries., Nutrient canals contain a neurovascular bundle derived from the inferior alveolar or dental neurovascular bundle. Nutrient canals are common in both dentulous and edentulous specimens and are found in approximately 16% of all mandibles. They are visible in dental radiographs, especially with increased age., Due to their high prevalence, some researchers consider them to be a normal anatomic condition., Most nutrient canals are classified as lingual canals since their origin/termination is on the lingual surface of the mandible, presenting as a lingual foramen. Lingual canals are most frequently located near midline, in proximity to the mental spines, but may also be positioned more laterally near the canine or premolar region. Nutrient canals may also be classified as buccal canals if their origin/termination is on the buccal surface of the mandible; many researchers actually classify the mental foramen as an enlarged buccal nutrient canal. In the current body literature, all nutrient foramen (regardless of lingual or buccal classification) has been localized to the mandibular body. While nutrient canals may be present in all segments of the mandible, a nutrient canal in the mandibular ramus has never been reported. Based on its definition and the possibility of broad localization, the authors have chosen to utilize the term “nutrient canal” to partially describe this case. It is important to note that the term “nutrient canal” is not a perfect representation of the case, both in terms of location and function. In the existing literature, no nutrient canal was described as involving a muscle; in the case study provided, the traversing vein is draining the masseter muscle. Thus, an abnormal venous connection is observed. In addition, the term “nutrient canal” in the literature has always suggested the delivery of nutrients, through an artery, whereas in this case no arterial vessel was observed. Thus, this anatomical case report is unique in many facets.
This case report is clinically significant in many regards. Anatomical variations, such as the one described in this case study, if unidentified, may lead to complications when performing procedures. Accessory foramen found in the mandibular ramus are vulnerable during sagittal split ramus osteotomies, osteogenic distractions, harvesting of bone blocks, and reconstructive surgery. Complications, such as bleeding, hematoma, or bruising, may result if the traversing structures are injured., Therefore, knowledge of these anatomical variations is crucial to ensure adequate patient care.
| Case Report|| |
During a routine anatomical dissection for dental students, an anomalous foramen was observed in the left mandibular ramus of an adult 93-year-old male dentulous cadaver. No anomalies were found on the right mandible.
While dissecting the temporal region and face, careful reflection of the masseter muscle revealed a venous structure on the deep surface which traversed through an unknown foramen on the mandibular ramus [Figure 1]. No artery or nerve was found accompanying the vein. To determine the origin of this unknown vessel, the infratemporal fossa was accessed. The zygomatic arch was incised with two vertical saw cuts corresponding to the anterior and posterior attachments of the masseter muscle. Reflection of the zygomatic arch and attached masseter muscle displayed the lateral surface of the mandibular ramus. The masseter muscle was then completely reflected, cutting the abnormal vein. The accessory foramen presented as a channel penetrating the buccal cortical plate and measured approximately 2 mm in diameter. To determine, if the foramen also passed through the lingual cortical plate, a saw was utilized to remove a portion of the mandibular ramus. Horizontal saw cuts were made inferior to the coronoid and condylar processes as well as a saw cut through the mandibular ramus immediately above the mandibular canal [Figure 2]. Removal of the intervening bone revealed an intact medial surface of the mandibular ramus. The accessory foramen was not seen perforating through the medial (lingual) cortical plate. Because the accessory canal passed through the buccal cortical plate and entered into the cancellous portion of the bone, the term “nutrient foramen” best describes this case. Examination of the infratemporal fossa exposed the standard anatomy. The pterygoid plexus, inferior alveolar nerve, artery, and vein, lingual nerve, and pterygoid muscles were unremarkable [Figure 3].
|Figure 1: Examination of the accessory nutrient foramen and traversing vein. Partial reflection of the masseter muscle demonstrates an accessory foramen (black arrow) with a traversing vein draining the deep surface of the muscle. Cor: Coronoid process, FA: Facial artery, FV: Facial vein, MF: Mental foramen|
Click here to view
|Figure 2: Access to the infratemporal fossa. Complete reflection of the masseter muscle demonstrates the accessory foramen (black arrow) in the center of the mandibular ramus. Dashed lines indicate future saw cuts to assess the relationship between the accessory foramen and infratemporal fossa. Temp m.: Temporalis muscle, Cor: Coronoid process, Con: Condylar process, FA: Facial artery, FV: Facial vein|
Click here to view
|Figure 3: Unremarkable infratemporal fossa anatomy. Removal of a portion of the mandibular ramus demonstrates a typical infratemporal fossa. Cor: Coronoid process, Con: Condylar process, FV: Facial vein, PtP: Pterygoid plexus, IAN: Inferior alveolar nerve, IAA: Inferior alveolar artery, IAV: Inferior alveolar vein, LN: Lingual nerve|
Click here to view
To determine the full extent of the accessory nutrient canal, bone clippers were carefully used to remove the buccal cortical plate overlying the unknown channel. An identical process was used to remove the cortical bone corresponding to the mandibular foramen. The accessory nutrient canal was located anterior to the mandibular canal. A thin ridge of cortical bone separated the nutrient and mandibular canals for a short distance [Figure 4]. Near the antegonial notch, or the concavity where the facial vessels cross the mandible, this dividing cortical bone dissipated and both canals degenerated; the previously traversing vein and inferior alveolar bundle diverged into an unrecognizable plexus inside the cancellous bone. Therefore, in the region of the antegonial notch, the nutrient, and mandibular foramen could no longer be defined.
|Figure 4: Examination of the accessory nutrient canal. The accessory nutrient foramen and canal (indicated by the blue pin) is located anterior to and partitioned from the mandibular canal in the mandibular ramus. Cor: Coronoid process, Con: Condylar process, FV: Facial vein, IA: Inferior alveolar neurovascular bundle|
Click here to view
| Discussion|| |
The authors have utilized the terms “nutrient foramen” and “nutrient canal” because of all variants previously reported, these terms best describe the findings observed.
The nutrient foramen did not contain a complete neurovascular bundle derived from the inferior alveolar or dental neurovascular bundle, as traditionally described. In fact, the specimen described differs from the traditional definition of a “nutrient canal” in that it did not contain an artery providing the region nutrients. The specimen contained a single traversing vein that drained the deep surface of the masseter muscle; this is the first case that reports an abnormal venous relationship between a nutrient canal and muscle. While the masseter muscle is traditionally drained through tributaries of the pterygoid plexus and facial vein, this specimen also had venous drainage through an unknown vein that communicated with the mandibular cancellous bone. Clinically, this finding is significant; the presence of this anomalous vein and its drainage of the masseter muscle may serve as a possible route for the spread of infections or tumors. In addition, understanding this variation may avoid mistaking nutrient channels and foramina as pathosis when interpreting radiographs.
Nutrient foramen is almost exclusively localized to the region of the incisors, canines, or premolars; all nutrient foramen previously reported have been localized to the mandibular body., This is the first case that reports a nutrient foramen in the ramus of the mandible. Clinically, knowledge of this variant is crucial. Clinical procedures such as intraoral vertical ramus osteotomies and sagittal split ramus osteotomies require intimate knowledge of the mandibular ramus. In addition, recognizing the possibility of accessory nutrient foramen in the mandibular ramus is critical during distraction osteogenesis of vertical mandibular ramus hypoplasia. In the case of reconstruction, the mandibular ramus often serves as a donor site for membranous cortical grafts. Being aware of mandibular ramus nutrient foramen, such as the one described in this case, is vital to avoid injuring traversing neurovascular structures and future complications. Therefore, thorough knowledge of these anatomical variations is important in minimizing risks during numerous procedures.
To the author's knowledge, there is no clear embryological explanation for the novel findings. Typical nutrient foramen is crucial for the development of bone during embryonic stages and the active growth phases. Once the periosteal layer of bone is established, angiogenic signaling results in nutrient invasion, the ramification of vessels, and the formation of trabeculae. Because bone remodeling is a dynamic and evolving process, the morphology of nutrient foramen and their associated canal usually change throughout development. Nutrient arteries are usually kept patent until growth is completed and sometimes even after growth. More specific to the mandible, accessory foramen near the mandibular canal, mental foramen, or retromolar area has been described as an invasion of inferior alveolar or mental neurovascular bundles.,,,, The accessory foramen of the mandibular ramus described in this case is not entirely explained by these hypotheses since no arterial or nervous structure was found traversing the nutrient foramen. Future research should address the developmental basis for accessory nutrient foramen in the mandibular ramus.
| Conclusion|| |
This case study describes an accessory nutrient foramen that differs in its contents and anatomical location compared to all other published samples. This study adds to the current body of literature reporting anatomical variations in mandibular osteology and is unique in its immense clinical relevance. Future investigations should examine the prevalence of accessory foramen on the mandibular ramus and involvement of venous drainage of surrounding muscles.
The cadaver used in this study was donated to the Body Donation Program at UT Health San Antonio for education and research. UT Health San Antonio is a member institution of the State Anatomical Board of Texas. All donations to the program are regulated and cared for under the statutes and guidelines of the State of Texas. UTHSCSA Office of IRB deemed the project to be non-regulated research. Patient consent is not applicable.
The authors would like to acknowledge the individual that has donated their body to science; their gift is recognized as an unparalleled educational tool.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Iwanaga J, Kikuta S, Tanaka T, Kamura Y, Tubbs RS. Review of risk assessment of major anatomical variations in clinical dentistry: Accessory foramina of the mandible. Clin Anat 2019;32:672-7.
Anderson LC, Kosinski TF, Mentag PJ. A review of the intraosseous course of the nerves of the mandible. J Oral Implantol 1991;17:394-403.
Choi YY, Han SS. Double mandibular foramen leading to the accessory canal on the mandibular ramus. Surg Radiol Anat 2014;36:851-5.
Langlais RP, Broadus R, Glass BJ. Bifid mandibular canals in panoramic radiographs. J Am Dent Assoc 1985;110:923-6.
Truong MK, He P, Adeeb N, Oskouian RJ, Tubbs RS, Iwanaga J. Clinical anatomy and significance of the retromolar foramina and their canals: A literature review. Cureus 2017;9:e1781.
Robinson C, Yoakum CB. Variation in accessory mental foramen frequency and number in extant hominoids. Anat Rec (Hoboken) 2020;303:3000-13.
Lovett DW. Nutrient canals; a roentgenographic study. J Am Dent Assoc 1948;37:671-5.
Ryder WB. The significance of “circulatory canals” in roentgenograms of the alveolar process. Am J Orthod Oral Sur 1942;28:640-51.
Kawashima Y, Sekiya K, Sasaki Y, Tsukioka T, Muramatsu T, Kaneda T. Computed tomography findings of mandibular nutrient canals. Implant Dent 2015;24:458-63.
Sweet AP. A statistical analysis of the incidence of nutrient channels and foramina in five hundred periapical full-mouth radiodontic examinations. Am J Orthod Oral Sur 1942;8:427-42.
Patel JR, Wuehrmann AH. A radiographic study of nutrient canals. Oral Surg Oral Med Oral Pathol 1976;42:693-701.
Kawai T, Asaumi R, Kumazawa Y, Sato I, Yosue T. Observation of the temporal crest canal in the mandibular ramus by cone beam computed tomography and macroscopic study. Int J Comput Assist Radiol Surg 2014;9:295-9.
Cunningham CA, Black SM. The vascular collar of the ilium: Three-dimensional evaluation of the dominant nutrient foramen. Clin Anat 2013;26:502-8.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]