A Case of Depressed Skull Fracture of the Inner Table Alone

Korean J Neurotrauma. 2021 Apr;17(1):67-69 https://doi.org/10.13004/kjnt.2021.17.e11 pISSN 2234-8999·eISSN 2288-2243

Case Report A Case of Depressed Skull Fracture of the Inner Table Alone

Ki Seong Eom

Department of Neurosurgery, Wonkwnag University Hospital, Institute of Wonkwang Medical Science, Wonkwang University School of Medicine, Iksan, Korea

Received: Mar 9, 2021 ABSTRACT Accepted: Apr 14, 2021

Address for correspondence: A depressed skull fracture (DSF) is comminuted fractures in which the broken bones displace Ki Seong Eom inward due to a blunt head trauma, such as when the broken outer table is located below the Department of Neurosurgery, Wonkwnag normal anatomical position of the inner table. The author presents an extremely rare case of University Hospital, Institute of Wonkwang Medical Science, Wonkwang University School a 38-year-old man with a DSF that affected only the inner table. In the literature, only 2 cases of Medicine, 895 Muwang-ro, Iksan 54538, of DSF involving only the inner table have been reported, and the underlying mechanism Korea. remains unclear. The author believes that this phenomenon was not enough for the impact E-mail: [email protected] force to depress the outer table, but the tensile stress was sufficient to depress the relatively thin and weak inner table. Copyright © 2021 Korean Neurotraumatology Society Keywords: Depressed skull fracture; Head trauma; Impact force; Tensile stress This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https:// creativecommons.org/licenses/by-nc/4.0/) INTRODUCTION which permits unrestricted non-commercial use, distribution, and reproduction in any 4) medium, provided the original work is properly The skull consists of 3 layers: the inner table, diploe, and outer table. A depressed skull cited. fracture (DSF) is comminuted fractures in which the broken bones displace inward due to a blunt trauma, such as when the broken outer table is located below the normal anatomical ORCID iDs 1) Ki Seong Eom position of the inner table. Here, the author presents an extremely rare case of DSF that https://orcid.org/0000-0002-8354-4024 affected only the inner table and also discuss the underlying mechanism.

Conflict of Interest The author has no financial conflicts of interest. CASE REPORT

A 38-year-old man was admitted due to a headache after a motorcycle accident. The neurological examination findings were unremarkable. Cranial computed tomography (CT) scan revealed DSF in the inner table of the left parietal bone and a linear fracture in the right temporal and left parietal bone. Three-dimensional (3D) skull CT revealed a DSF of the inner table and a linear facture connected to the right lambdoid suture (FIGURE 1). Cranial magnetic resonance imaging revealed a hemorrhagic brain contusion just below the DSF and injured diploe (FIGURE 2). The patient's clinical course was unremarkable, and the patient was discharged 2 weeks after conservative treatment without any neurological deficits. The study was approved by the Institute Ethical Committee and in compliance with institute's requirements (202008011). https://kjnt.org 67 Fracture of Inner Table Alone

A B

C D

FIGURE 1. (A, B) Cranial CT scan with bone setting showing a DSF of the inner table of the left parietal bone and a linear fracture of the right temporal and left parietal bone. (C, D) Three-dimensional skull CT showing DSF of the inner table and linear facture connected to the right lambdoid suture. CT: computed tomography, DSF: depressed skull fracture.

A B

FIGURE 2. T1-weighted (A) and T2-weighted (B) magnetic resonance imaging showing the hemorrhagic brain contusion just below the depressed skull fracture and injured diploe. DISCUSSION

In the literature, only 2 cases of DSF involving only the inner table have been reported, and the underlying mechanism remains unclear. In 1898, Standage found DSF of the inner table over the Rolandic fissure during surgery on an injured Somali soldier.3) He mentioned that the fragments of the inner table did not radiate from the impact point was unusual. He thought it was not inconsistent with the diffusion of force widely over the table that was not directly struck. In 2016, Miyake et al.2) reported a DSF of only the inner table of the right parietal bone in a 22-year-old patient after a fall. They explained this phenomenon as being https://kjnt.org https://doi.org/10.13004/kjnt.2021.17.e11 68 Fracture of Inner Table Alone

the result of a strong tensile stress on the inner table due to blunt trauma through a literature review of computer simulations. They suggested that von Mises stress, in which the inner table exerts a higher stress than the outer table, and the first principal stress that affected the inner table was tensile stress and the first to affect the outer table was compressive stress. Because the structure of the skull is complex and 3D, impact forces are routinely transmitted to the skull in a variety of ways.4) Blunt trauma can cause complex fractures that are linear or radiate, concentric, and depressed. The ductility of the bone allows it to bend to fit the impacting object and then approximately recover its initial shape when the load stops.1) Skull fractures can occur either due to focal or general deformity. When the skull receives a focal impact from a moving object, such as a hammer or brick, there is a momentary distortion of the shape of the cranium. The area under the impact bends inwards, leading to a compensatory distortion or bulging of other areas. On the other hand, when the skull is deformed by the head in motion striking an object, such as in falls and traffic accidents, compression occurs at the concavity of the curved bone and the tension force acts on the convexity because the skull is compressed like an elastic sphere. The cause of DSF in Miyake's patient was a fall and the cause was a motorcycle accident in the present patient. In both cases, the impact of the dynamic load resulted in a DSF of the inner table of the parietal bone. Unlike Miyake's patients, the present patient had a linear fracture of the outer table, which was connected to the periphery of the DSF. The author believes that this phenomenon was not enough for the impact force to depress the outer table, but the tensile stress was sufficient to depress the relatively thin and weak inner table. Although DSF of only the inner table is an extremely rare type of skull fracture, it may cause serious brain injury. Therefore, further observations are necessary to clarify this phenomenon.

ACKNOWLEDGEMENTS

This paper was supported by Wonkwang University in 2020.

REFERENCES

1. Delannoy Y, Becart A, Colard T, Delille R, Tournel G, Hedouin V, et al. Skull wounds linked with blunt trauma (hammer example). A report of two depressed skull fractures--elements of biomechanical explanation. Leg Med (Tokyo) 14:258-262, 2012 PUBMED | CROSSREF 2. Miyake S, Yamamura K, Abe H. A case of depressed skull fracture involving only the inner table. No Shinkei Geka 44:599-603, 2016 PUBMED | CROSSREF 3. Standge RF. A case of fracture of inner table of the skull without injury to the outer table. Lancet 152:1388- 1389, 1898 CROSSREF 4. Yoganandan N, Pintar FA. Biomechanics of temporo-parietal skull fracture. Clin Biomech (Bristol, Avon) 19:225-239, 2004 PUBMED | CROSSREF

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