Yuwa Clinic

Overview of MTBI

MTBI stands for mild traumatic brain injury. It is referred to as an invisible brain injury. Why is it called invisible?　This is due to the fact that it cannot be detected on traditional CT or MRI imaging.

Because MTBI is caused by a "violent shaking impact" of the head like whiplash, which results in microscopic tearing to cranial nerve fibers that can be detected with a microscope (axonal fiber damage), it cannot be visualized with CT or MRI, is considered normal, and is left untreated and without medical care or compensation.

In recent years, imaging techniques have been developed to make these invisible wounds visible: fiber tractography, an MRI-based technique that visualizes brain nerve fibers by imaging the flow of water in nerve bundles, is the most suitable technique for MTBI and can depict the wounds in about 60% of people with MTBI. The others are SPECT and PET, which can depict decreased blood flow in the brain due to MTBI. SPECT is a technique to image cerebral blood flow by injecting a radioisotope that binds to brain tissue. This allows brain damage to be manifested.

Due to the damage to the nerve fibers in the brain, MTBI patients often have disabilities such as forgetting to turn off the gas, forgetting keys or cell phones, difficulty understanding conversations, difficulty with speech, difficulty doing two things at once, and personality changes such as becoming angry.

How MTBI occurs

Neurons in the brain are made up of neuronal cell bodies, short dendrites and long axons (axon fiber), from the cell bodies. In MTBI, the axon fibers are mainly damaged. When this occurs extensively, it is called diffuse axonal injury.

Figure 5-2 shows how axonal damage occurs. As shown, when a rotational impact occurs to the head, such as whiplash, a twisting force acts on the axon, resulting in a tear of the axon. Then, axons drop out, collapse, and nerve cells become inactive and necrotic.

Depending on the location of the lost or disintegrated axons, the patient may experience impaired consciousness, higher brain dysfunction, brain localization functional signs, cranial nerve palsy, motor and sensory palsy in the limbs, cerebellar symptoms, vesico-rectal disorders, and extrapyramidal disorders.

Diagnostic criteria for MTBI

In 1993, the American Association for Rehabilitation Medicine (AARM) first published a definition of MTBI. The key point to be evaluated in this criterion is that loss of consciousness is not an absolute condition, but that MTBI can be diagnosed if the following items are satisfied. The criteria include mild alterations in consciousness, such as fainting, disorientation and clouding of consciousness, traumatic amnesia and focal neurological deficit symptoms.

The diagnostic criteria for MTBI as reported by WHO in 2004 is basically the criteria follow those of AARM.

Frequency of MTBI and sequelae

It has been reported that in the clinical course of Mild TBI, there are 7% to 33% of cases in which symptoms are left behind and do not heal and become chronic. It is estimated that 2% of Americans, or 5.3 million people, are currently living with the sequelae of TBI. A similar high incidence is estimated in our country.

Thus, MTBI is a disease of high frequency of occurrence; the only diseases more frequent than MTBI are migraine headaches and shingles.

Depending on the country, it is estimated that between 100 and 500 cases of MTBI occur per 100,000 population. One report estimates that there are 180 cases of MTBI per 100,000 population, of which 15%, or 27 cases, have prolonged symptoms. This is a very large frequency.

Fiber tractography

Fiber tractography(Hereinafter referred to as FT) in a case of diffuse axonal injury by a traffic accident

Figure 5-4 shows FT of a case of higher brain dysfunction by a traffic accident (with intellectual, attention, memory and executive function impairments) by Ken Sugiyama et al. In this case, conventional CT/MRI can’t detect any abnormalities, but FT shows more pronounced damage to the corpus callosum and fornix compared to healthy subjects in the left column.

SPECT (cerebral blood flow scintigraphy)

Brain SPECT test stands　for single photon emission computed tomography of the brain. A small dose of a fat-soluble radiopharmaceutical that tends to accumulate in the brain is injected. The distribution of radiation (gamma rays) emitted by the drug that accumulates in the brain is photographed by a scintillation camera and displayed as a tomographic image. This detects localized reduced blood flow due to brain damage.

In head trauma, brain SPECT images are useful for understanding the pathophysiology, diagnosis, treatment, prognosis, and efficacy of treatment. SPECT has the advantage that the whole brain can be evaluated and statistical analysis images can be easily generated by comparison with standard databases.

A case of cerebral hypoperfusion on SPECT: 53-year-old male.　Two years ago, he suffered loss of consciousness due to traffic trauma and was treated at another hospital as concussion. After returning to work, he showed decreased concentration, memory, and work efficiency. Symptoms such as headache, dizziness, tremor, and numbness also persisted. Brain MRI showed no obvious brain contusion, but white matter lesions in the bilateral frontal subcortex. SPECT showed decreased blood flow in the bilateral frontal lobes, and this finding did not change when examined 2 and 3 years after head injury, indicating irreversible neurological damage. The patient was diagnosed as having higher brain dysfunction. (From Hiroshi Matsuda: The Perfect Guide to Brain SPECT)

Cases of MTBI

The following sections describe cases of MTBI and moderate TBI that we have diagnosed or treated.

Case 1

Case 2