Transcript ABSTRACT ID NO: 1159

ABSTRACT ID NO: 1159
HYPERTROPHIC INFERIOR
OLIVARY NUCLEUS
DEGENERATION- AN ENIGMA
BACKGROUND
• Hypertrophic inferior olivary nucleus degeneration is a rare entity that
occurs due to a unique type of transneuronal degeneration resulting from a
primary lesion in the Guillain-Mollaret triangle.
• This condition is unique owing to the fact that the degeneration results in
hypertrophy rather than atrophy of the nucleus.
• MRI appearances vary according to the duration from the initial insult as
well as the pathological stages.
• We hereby report two cases diagnosed at our institution, one following
pontine hemorrhage and another following posterior fossa epidermoid cyst
excision.
LEARNING OBJECTIVES
• Hypertrophic inferior olivary nucleus degeneration is an entity that occurs
when there is a focal pathology involving the the dentato-rubral-olivary
pathway which is known as the Guillain- Mollaret triangle.
• The Guillain-Mollaret triangle connects the ipsilateral red nucleus and the
inferior olivary nucleus with the contralateral dentate nucleus.
Figure 1- shows the pathway of the Guillain
Mollaret triangle. Efferent fibers from the dentate
nucleus in the cerebellum (orange dot) traverse in
the superior cerebellar peduncle to the contralateral
red nucleus in the midbrain (red dot). From here,
efferent fibres traverse via the central tegmental
tract to the ipsilateral inferior olivary nucleus in the
brainstem (yellow dot). The pathway ends with
efferent fibers from the inferior olivary nucleus
traversing via the inferior cerebellar peduncle to the
contralateral dentate nucleus.
• Hypertrophic olivary nucleus degeneration can occur secondary to lesions
affecting the first two limbs of the triangle and not from lesions involving
the olivo-dentate fibres.
ETIOLOGY:
-Common pathologies that can cause this condition are:
a)
b)
c)
d)
e)
f)
g)
Hemorrhage
Cavernous hemangioma
Vascular malformations
Infarction
Trauma
Surgery for posterior fossa lesions
Idiopathic.
CLINICAL FEATURES:
• Typically the onset of pathology is typically three weeks after the initial
insult. However, the time of onset of symptoms varies.
• Patients usually present with Holmes’ tremor, palatal myoclonus and
ocular myoclonus.
• Palatal myoclonus may not always be seen in patients with hypertrophic
olivary degeneration.
`
PATHOLOGY:
• According to Goto et al, six phases of pathological changes are seen from
the time of onset.
a)
b)
c)
d)
e)
f)
No change within 24 hours.
Degeneration of olivary anniculum after 7 days.
Mild olivary hypertrophy until 3 weeks.
Olivary enlargement until 8.5 months.
Olivary pseudohypertrophy until 9.5 months.
Olivary atrophy after years.
MRI FEATURES:
• Hypertrophic olivary degeneration cannot be evaluated with MRI till the
pathology reaches the third phase of mild olivary hypertrophy.
• On MRI, the classic finding is T2W/FLAIR hyperintensity and enlargement
of the inferior olivary nucleus located in the brainstem which shows no
diffusion restriction or abnormal enhancement.
• Patterns of presentation:
Three patterns of presentation can occur depending on the site of the primary lesion
in the dentato-rubral-olivary pathway.
Unilateral and ipsilateral
- lesion in the brainstem.
Unilateral and contralateral - lesion in cerebellum/cerebellar
peduncles.
Bilateral
- Midline lesion at the point of
decussation/lesion in ipsilateral
brainstem and cerebellum.
• According to Goyal and Birbamer, hypertrophic olivary degeneration
changes in MRI occurs in three stages:
a) T2 FLAIR signal hyperintensity without hypertrophy of the inferior
olivary nucleus (occurs 4-6 months after primary insult).
b) T2W/FLAIR signal hyperintensity with hypertrophy of the inferior
olivary nucleus (occurs from 6-16 months after primary insult).
c) Resolution of hypertrophy with/without atrophy and persistent signal
hyperintensity in T2W/FLAIR images (occurs 16 months after primary
insult)
d) 3-4 years after the lesion, hypertrophy resolves and a faint linear or
punctate hyperintensity can persist.
DIFFERENTIAL DIAGNOSIS:
• Focal T2 signal hyperintensity involving the antero-lateral part of the
medulla alone is not diagnostic of Hypertrophic inferior olivary nucleus
degeneration since similar changes can be seen in:
a)
b)
c)
d)
e)
Infarction
Demyelination
Infections-AIDS, TB.
Sarcoidosis
Tumors like lymphoma, astrocytomas, metastases.
CASE 1
• A 42 year old male patient who was a known case of fourth ventricle
epidermoid cyst and underwent tumor excision 6 months prior, presented
with complaints of progressive diplopia, gait disturbance ,weakness of the
right hand with difficulty in writing, slurring of speech which began about
one month following surgery .
• On examination, there was right sixth cranial nerve palsy with gaze evoked
nystagmus, right cerebellar signs and visible palatal myoclonus.
• Patient was referred to our department for a contrast MRI Brain.
FIGURE : 2
FIGURE : 3
FIGURE : 4
Axial MRI images showing residual post operative changes seen as altered
signal intensity around the fourth ventricle and right inferior cerebral peduncle
which appear hypointense on T1W image (Figure 2) and hyperintense on T2
FLAIR (Figure 3) and T2W image (Figure 4).
Figure 5: Axial T2W image shows postoperative changes around the fourth
ventricle (blue arrow) and right middle
cerebellar peduncle (red arrow).
Figure 6: DWI shows a small residual
lesion in the fourth ventricle (yellow arrow)
with restriction of diffusion.
FIGURE : 7
FIGURE : 8
FIGURE : 9
Mild oblong hypertrophy and hyperintensity of bilateral inferior olivary nucleus
(yellow arrow) seen in Axial T2W (Figure 7), Axial FLAIR (Figure 8) and Coronal
T2W (Figure 9) images.
Figure 10: Post-contrast T1W axial image
shows no enhancement of the hypertrophied
inferior olivary nuclei (yellow arrow).
Figure 11: DWI shows no restricted diffusion
in the region of inferior olivary nuclei.
CASE 2
• A 50 year old hypertensive male patient, presented with weakness in left
upper and lower limbs since three months and progressive slurring of
speech since one month.
• He had a past history of acute onset of left hemiparesis, slurring of speech
and right third cranial nerve palsy three months back. A CT brain taken at
the time showed acute brain stem hemorrhage and chronic infarcts in the
basal ganglia region.
• On examination, hypotonia was present in the left upper and lower limbs,
left plantar reflex was extensor and right third cranial nerve palsy was
present. Palatal myoclonus was absent.
• Patient was referred to the Department of Radiology for a contrast MRI
Brain.
FIGURE : 11
FIGURE :12
FIGURE : 13
Axial MRI images show chronic hemorrhage in the right side of midbrain
(Figure 11) and central and posterior aspect of the Pons and the cerebral
peduncle (Figure 12) which shows susceptibility artifact on T2 FFE image
(Figure 13).
FIGURE : 14
FIGURE : 15
FIGURE : 16
Oblong hypertrophy and hyperintensity of right inferior olivary nucleus (red
arrow) seen in Axial T2W (Figure 14), Coronal T2W (Figure 15) and Axial
T2W FLAIR (Figure 16) images.
Figure 18: Post-contrast T1W axial image
shows no enhancement of the
hypertrophied right inferior olivary nucleus.
Figure 19: DWI shows no restricted
diffusion in the region of the right inferior
olivary nucleus.
CONCLUSION
• Hypertrophic inferior olivary nucleus degeneration is a rare entity that can
be missed or erroneously diagnosed.
• The presence of an inciting lesion in the brainstem or cerebellum, signal
changes confined to the olivary nucleus with or without enlargement and
absence of contrast enhancement together help to cinch the diagnosis.
REFERENCES
• 1. Goto N, Kaneko M. Olivary enlargement: Chronological and
morphometric analyses. Acta Neuropathol 1981;54:275-82.
• 2.Goyal M, Versnick E et al. Hypertrophic olivary degeneration:
Metaanalysis of temporal evolution of MR findings. AJNR Am J
Neuroradiol July 2000;21:1073-1077.
• 3.Vaidhyanath R, Thomas A, Messios N. Bilateral hypertrophic olivary
degeneration following surgical resection of a posterior fossa epidermoid
cyst. The Bristish Journal of Radiology 2010;83:e211-e215.
• 4.Sen D, Gulati YS, Malik V, Mohimen A, Sibi E, Reddy DC. MRI and MR
Tractography in bilateral hypertrophic inferior olivary degeneration. Indian
J Radiol Imaging 2014;24:401-5.