Involved lesions (probable)
Case 91
【Progress】They are continuing rehabilitation in our hospital.
【Discussion】
Medial lemniscus is present at medulla, pons and midbrain. Medial lemniscus is part of the posterior column-internal lemniscus pathway which transmits vibratory and touch sense and ascends from skin to thalamus via nucleus gracilis & nucleus cuneatus in the medulla. Namely, medial lemniscus is composed of axons from these nuclei. Medial lemeniscus situates at the center and the middle of the pons on axial images. Patient 1 (Case 1) and Patient 2 (Case 2) experienced hemi-lateral sensory deficit. MRI with diffusion weighted imagings of both cases showed the damage corresponded to medial lemniscus.
Lateral spinothalamic tract and lateral lemniscus situate at lateral sides of medial lemniscus. Lateral spinothalamic tract transmits pain and temperature sense. Lateral lemniscus transmits sound sense and is composed of axons between inferior colliculus and cochlear nucleus. Patient 1 (Case 1) and Patient 2 (Case 2) experienced sensory damages of pain and temperature but not deafness, indicating the damage of spinothalamic tract but not lateral lemniscus.
There exist four brain nerves nuclei in the pons: trigeminal nerve nucleus, abduct nerve nucleus, facial nerve nucleus and vestibular nerve nucleus. These nuclei situate at the dorsal side from internal lemniscus, between fourth ventricle and internal lemniscus. Trigeminal n nuclei situate at the upper-dorsal area compared to internal meniscus. Vestibular n nuclei situate at the inferior-dorsal area. Trigeminal nerves and vestibula nerves branch from the ventral side of pons, implying that these neural roots traverse from the most dorsal side to the ventral side. These neural roots pathways are susceptible to pons infarction or hemorrhage. In Patient 1 (Case 1) experienced sensory deficit of face and tinnitus, indicating that these nerve roots course might be damaged based on MRI findings (Figs 1B, 1C).
There are three cerebellar peduncles; superior, middle and inferior cerebellar peduncles. Of these three peduncles, middle cerebellar peduncle comes out from the pons via pontine nucleus which transmit from cortex to cerebellum. Although pontine nuclei situate at the most anterior (ventral) part of pons, middle cerebellar peduncle might be damaged in Case 1 based on hemiparesis and MRI findings (Figs 1 A-C).
Cortico-nuclear tract transmits signals from cortex to brain nerve nuclei of facial n nucleus, glossopharyngeal n nucleus, vagus n nucleus and hypoglossal n nucleus (motor neuron). Cortico-nuclear tract situates just dorsally from internal lemniscus, namely between internal lemniscus and forth ventricle. The damage of this tract causes dysarthria and dysphagia.
Corticospinal tract and corticopontine tract are motor neuron and situate at the ventral side of pons, inducing ventral bulging of pons. In Case 2, MRI with DWI showed fresh infarction of ventral side of pons, indicating damages of these tracts caused hemiparesis on the contralateral side.
【Summary】
We present two cases with pontine damages of hemorrhage or infarction. MRI showed main damages of internal lemniscus and spinothalamic tract which sensory neuron in Case 1, and main damages of both motor neuron pathway of corticospinal tract and corticopontine tract, and sensory neuron pathway of internal lemniscus and spinothalamic tract in Case 2. We should keep in mind that ventral side of pons holds corticospinal tract and corticopontine tract and pontine nucleus, mid-part of pons holds internal lemniscus, spinothalamic tract and lateral lemniscus. Dorsal central side holds extrapyramidal tract of internal longitudinal fasciculus, central tegmentum tract (extrapyramidal tract connecting between the red nucleus and the inferior olivary nucleus) and tectospinal tract (connecting from superior colliculus to cervical spinal cord). Dorsal lateral side holds brain nerve nuclei: trigeminal n nucleus (V), abducens n nuclei (VI), facial n nuclei (VII) and vestibular n nuclei (VII).
【References】
The content of this article is written by the book as below.
Peter Duus. Neuroloigisch-topische Diagnostik: Anatomie Physiologie Klinik, second edition translated in Japanese by Hajime Handa and Junya Hanakita. Bunkodo, Tokyo
2018.2.7