Journal of Clinical Neuroscience xxx (2015) xxx–xxx

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Journal of Clinical Neuroscience
journal homepage: www.elsevier.com/locate/jocn

Case Report

Hypertrophic olivary degeneration secondary to pontine haemorrhage
Sara Wein a,⇑, Bernard Yan b, Frank Gaillard a,c
a

Department of Radiology, First Floor, 1B Building, The Royal Melbourne Hospital, Grattan Street, Parkville, VIC 3050, Australia
Department of Neurology, The Royal Melbourne Hospital, Parkville, VIC, Australia
c
Department of Radiology, The University of Melbourne, Parkville, VIC, Australia
b

a r t i c l e

i n f o

Article history:
Received 9 February 2015
Accepted 14 February 2015
Available online xxxx
Keywords:
Cavernoma
Hypertrophic olivary degeneration
MRI
Palatal myoclonus
Pontine haemorrhage

a b s t r a c t
We report a 58-year-old man who developed hyptertrophic olivary degeneration (HOD) after
haemorrhage of a cavernous malformation in the pons. Lesions of the triangle of Guillain and Mollaret
(the dentatorubro-olivary pathway) may lead to HOD, a secondary transsynaptic degeneration of the
inferior olivary nucleus. HOD is considered unique because the degenerating olive initially becomes
hypertrophic rather than atrophic. The primary lesion causing pathway interruption is often
haemorrhage, either due to hypertension, trauma, surgery or, as in our patient, a vascular malformation
such as a cavernoma. Ischaemia and demyelination can also occasionally be the inciting events. The
classic clinical presentation of HOD is palatal myoclonus, although not all patients with HOD develop this
symptom. The imaging features of HOD evolve through characteristic phases. The clue to the diagnosis of
HOD is recognition of the distinct imaging stages and identification of a remote primary lesion in the
triangle of Guillain and Mollaret. Familiarity with the classic imaging findings of this rare phenomenon
is necessary in order to avoid misdiagnosis and prevent unnecessary intervention.
Crown Copyright Ó 2015 Published by Elsevier Ltd. All rights reserved.

1. Introduction
Lesions of the triangle of Guillain and Mollaret (the dentatorubro-olivary pathway) may lead to hyptertrophic olivary degeneration (HOD), a secondary transsynaptic degeneration of the inferior
olivary nucleus (ION). HOD is considered unique because the
degenerating olive initially becomes hypertrophic rather than
atrophic. The primary lesion causing pathway interruption is often
haemorrhage, either due to hypertension, trauma, surgery or a vascular malformation such as a cavernoma. Ischaemia and demyelination can also occasionally be the inciting events.
2. Case report
A 58-year-old man presented to the emergency department
with acute onset of weakness of the right facial muscles and left
upper and lower extremities. His past medical history included
hypertension, intravenous drug use and alcoholic/hepatitis C cirrhosis (Child–Pugh score A). A non-contrast CT scan performed
on admission demonstrated an acute 11 mm right-sided pontine
haemorrhage (Fig. 1a). No abnormality was detected on CT angiogram. A routine follow up brain MRI performed 4 months later
⇑ Corresponding author. Tel.: +61 3 93427255; fax: +61 3 93428602.
E-mail address: sarawein@bigpond.com (S. Wein).

revealed a region of heterogeneous T1- and T2-weighted signal
in the dorsal right pons with prominent blooming on the susceptibility-weighted sequence but without significant contrast
enhancement, most consistent with a cavernoma (Fig. 1b). At that
time, the right ION was noted to be expanded and demonstrated
high T2 signal characteristic of HOD (Fig. 1c, d).
3. Discussion
HOD is a secondary transsynaptic degeneration of the ION
caused by a lesion in the triangle of Guillain and Mollaret (the dentatorubro-olivary pathway) (Fig. 2). The triangle, initially described
by Guillain and Mollaret in 1931 [1], consists of the ION, the contralateral dentate nucleus (DN) and the ipsilateral red nucleus
(RN). Fibres connecting the DN and RN ascend through the superior
cerebellar peduncle (dentatorubral tract) and the central tegmental tract connects the RN to the ION. The triangle is completed by
fibres that cross from the ION to the contralateral DN via the inferior cerebellar peduncle (olivodentate fibres).
HOD is caused by lesions in the dentatorubral or central
tegmental tracts, as disruption of these pathways leads to functional deafferentation of the ION. Isolated lesions of the inferior
cerebellar peduncle do not result in HOD as anatomically there
are no direct connections between the ION and the contralateral
DN. Rather, inferior fibres in the inferior cerebellar peduncle from

http://dx.doi.org/10.1016/j.jocn.2015.02.005
0967-5868/Crown Copyright Ó 2015 Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Wein S et al. Hypertrophic olivary degeneration secondary to pontine haemorrhage. J Clin Neurosci (2015), http://
dx.doi.org/10.1016/j.jocn.2015.02.005

2

Case Report / Journal of Clinical Neuroscience xxx (2015) xxx–xxx

Fig. 1. Non-contrast axial CT scan performed on admission demonstrates an acute
right-sided pontine haemorrhage (A). T2-weighted axial MRI performed 4 months
later demonstrates a region of low signal intensity within the dorsal right pons at
the site of haemorrhage (arrow), most consistent with a cavernoma (B). T1weighted axial MRI sequence through the medulla demonstrates expansion of the
right inferior olivary nucleus (C; arrow). T2-weighted axial MRI sequence of this
region demonstrates increased signal intensity of the right inferior olivary nucleus
(D; arrow), characteristic of hypertrophic olivary degeneration.

The primary lesion causing pathway interruption is often haemorrhage, either due to hypertension, trauma, surgery or, as in
our patient, a vascular malformation such as a cavernoma.
Ischaemia and demyelination can also occasionally be the inciting
events. Lesions of the superior cerebellar peduncle cause contralateral HOD whereas primary lesions of the central tegmental tract
cause ipsilateral HOD. Bilateral HOD can occur if the primary lesion
involves both of the aforementioned structures.
The classic clinical presentation of HOD is palatal myoclonus
which is characterised by rhythmic involuntary movements of
the oropharynx due to contractions of the levator veli palatini
muscle and can sometimes also involve the larynx, tongue and
face. Palatal myoclonus usually develops 10 to 11 months after
the primary lesion, although not all patients with HOD develop this
symptom [4]. Occasionally, patients with HOD may develop a
dentatorubral tremor (Holmes tremor) of the upper limbs [5].
HOD is considered unique because the degenerating olive initially becomes hypertrophic rather than atrophic. Pathologically,
olivary enlargement corresponds to vacuolar degeneration of the
cytoplasm, glial hypertrophy and proliferation of gemistocytic
astrocytes [6]. Over time, the olive undergoes atrophy.
The imaging features of HOD evolve through characteristic
phases [3,7]. In the acute stage, the olive appears normal. After 1
month, the ION develops hyperintense T2-weighted signal.
Between 6 months and 3 to 4 years, the olive demonstrates hypertrophy and hyperintense T2-weighted signal. The hypertrophy
then resolves but the hyperintense T2-weighted signal persists
indefinitely. HOD typically does not enhance on contrast-enhanced
sequences, although cases of enhancement have been reported [8].
The diagnosis for HOD includes a wide variety of pathological
lesions that cause T2-weighted hyperintensity in the anterior
medulla. These include infarction, demyelination, tumour (astrocytoma, metastasis, lymphoma) and infectious/inflammatory processes such as tuberculosis, sarcoidosis and rhombencephalitis.
The clue to the diagnosis of HOD is the presence of a remote lesion
in the contralateral cerebellar DN or superior cerebellar peduncle,
or in the ipsilateral RN or pontine tegmentum. Familiarity with the
characteristic imaging findings of this rare phenomenon is necessary in order to avoid misdiagnosis and prevent unnecessary
intervention.
Conflicts of Interest/Disclosures
The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
References

Fig. 2. Coronal T1-weighted sequence demonstrates the Guillain–Mollaret triangle
which consists of the inferior olivary nucleus (O), the ipsilateral red nucleus (R) and
the contralateral dentate nucleus (D). The dentate nucleus and red nucleus are
connected by the dentatorubral tract, the red nucleus and inferior olivary nucleus
are connected by the central tegmental tract, and the inferior olivary nucleus and
dentate nucleus are connected by the olivodentate fibres.

the ION project first to the contralateral cerebellar cortex
(olivocerebellar tracts) and then to the DN [2]. When these fibres
are disrupted cerebellar atrophy can occur [3].

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Please cite this article in press as: Wein S et al. Hypertrophic olivary degeneration secondary to pontine haemorrhage. J Clin Neurosci (2015), http://
dx.doi.org/10.1016/j.jocn.2015.02.005