Hypertrophic olivary degeneration after posterior cranial fossa tumor resection in adults: illustrative case

Abstract

BACKGROUND

Posterior cranial fossa tumor resection can be complicated by a rare but potentially debilitating condition known as hypertrophic olivary degeneration (HOD). This condition is diagnosed using a high degree of clinical suspicion as well as T2/FLAIR MRI findings of nonenhancing, hyperintense enlargement of the inferior olivary nucleus.

OBSERVATIONS

The authors present a unique case of HOD in a 49-year-old female 4 months after resection of a low-grade pilocytic astrocytoma from the cerebellar vermis. The patient displayed classic signs associated with HOD, including palatal tremor, ocular nystagmus, and ocular myoclonus. Management will likely be challenging, and the patient was referred to movement disorder specialists to discuss potential treatment options.

LESSONS

Few case reports of HOD after neurosurgical intervention in adults are available in the literature. In this work, the authors conducted a literature review of available data for 23 cases of HOD in adult patients after midline posterior cranial fossa tumor resection. The prognosis of symptomatic HOD is generally poor, as no standardized treatment regimen for these patients currently exists.

https://thejns.org/doi/10.3171/CASE25130

Hypertrophic olivary degeneration (HOD) is a rare condition that occurs after disruption of the dentato-rubro-olivary pathway (DROP), a set of tracts also known as the Guillain-Mollaret triangle. Any component of the DROP, including the dentate nucleus, dentato-rubral tract, red nucleus, or rubro-olivary tract, may contribute to this unique form of neuronal degeneration.¹ Damage is most frequently associated with neurosurgical resection of a posterior cranial fossa (PCF) tumor; however, it can be caused by a wide variety of etiologies such as trauma or cerebrovascular incident.² Diagnostics for HOD are limited primarily to a high degree of clinical suspicion coupled with MRI findings of nonenhancing, hyperintense enlargement of the inferior olivary nucleus (ION) on T2/FLAIR imaging.²,³ HOD can be either unilateral or bilateral.^4–6 Clinically, HOD can remain asymptomatic with diagnoses made incidentally on routine follow-up imaging. When present, the most specific symptoms of this condition include palatal tremor, ocular myoclonus, and ocular nystagmus.⁷ Here, we report the case of a low-grade glioma resection with subsequent development of HOD and review the existing literature for this rare condition.

Illustrative Case

Patient Report

A 49-year-old female presented to our institution with a known 12-year history of a slowly enlarging fourth ventricular mass presumed to be a low-grade glioma. Her presenting symptoms were vertigo and nausea. Her medical history also included hypothyroidism, lymphocytic colitis, and irritable bowel syndrome. MRI showed an approximately 3-cm hypointense lesion of the cerebellar vermis abutting the fourth ventricle (Fig. 1A). She had previously been counseled against resection by an outside facility and followed with serial imaging. However, given her attributable symptoms, lesion growth, and encroachment on the fourth ventricle with impending obstructive hydrocephalus, resection was recommended.

FIG. 1.

A:Preoperative sagittal (left) and axial (right) T1-weighted MR images showing a hypointense lesion of the cerebellar vermis. B: Postoperative sagittal T1-weighted MR image (left) and axial T2/FLAIR images (right) showing recovery after tumor resection and bilateral hyperintense lesions of the medullary olives (dashed circles), respectively.

The patient underwent an uncomplicated gross-total resection via telovelar approach and pathology confirmed a WHO grade 1 pilocytic astrocytoma. Her postoperative MRI confirmed a gross-total resection. She was then discharged to rehabilitation after an uncomplicated hospital course. One month after her index surgery, she presented with continued symptoms and an enlarging posterior fossa pseudomeningocele, which eventually underwent primary repair followed by ventriculoperitoneal shunt placement.

At discharge she did not demonstrate any signs of cerebellar dysfunction or visual complaints. At clinical follow-up 2 months after resection, she described experiencing right hand clumsiness, difficulty speaking, and new-onset double vision. Neuroimaging at the time was reassuring without evidence of stroke, hemorrhage, problematic ventricular caliber, or other explanations for her new complaints. She was continuing with physical therapy and speech therapy and was now referred to neuro-ophthalmology. Her symptoms progressed and new MRI at 4 months postresection showed new bilateral globular hyperintense foci in the medullary olives on T2/FLAIR imaging (Fig. 1B). On physical examination, she now had a palatal tremor diagnosed by fiber-optic endoscopic evaluation of swallowing (FEES), ocular nystagmus and myoclonus, and moderate cerebellar mutism not immediately present after surgery.

Her combination of radiographic findings and neurological dysfunction were diagnostic for HOD, and she was referred to our movement disorder specialists to discuss potential treatment options. She was advised to continue with physical therapy, speech therapy, and occupational therapy. The option to begin anticholinergic or antidopaminergic medication was also discussed but not initiated at this time. One month later she reported improvement in speech, unsteadiness, and vision, yet her condition continues to be monitored.

Informed Consent

The necessary informed consent was obtained in this study.

Review of the Literature

This case displays characteristic findings of HOD, yet its presentation in an adult patient after a telovelar approach for a low-grade glioma is remarkably rare. HOD may be more frequent after cerebellar tumor resection in children, with incidences as high as 33% reported in some studies.^8–10 HOD may also be underdiagnosed, as many reports of HOD are asymptomatic. Rare cases of HOD have been reported in adults, predominantly in radiological and neurological journals.

We performed a literature review of the PubMed and Scopus databases using the terms “hypertrophic olivary degeneration” and “hypertrophic olives” to identify case reports and case series discussing HOD development after resection of PCF tumors. Search results were limited to patients older than 18 years of age who underwent neurosurgical resection of midline cerebellar or fourth ventricular tumors and later developed HOD. Reports involving pediatric cases or supratentorial procedures were excluded. Surgical approach (telovelar, transvermian, or paravermian) was noted when available (Table 1).

TABLE 1.

Literature review

Authors & Year	Age (yrs)/Sex	Tumor Type	Op Approach	Op to HOD Diagnosis, mos	HOD Site	HOD Symptoms
Akar et al., 200812	27/F	PA	—	2	Lt	—
Hirano et al., 201513	40/M	Medulloblastoma	—	0	Bilat	—
	46/M	Low-grade glioneuronal	—	3	Bilat	—
	42/M	Medulloblastoma	—	4	Bilat	—
	55/F	PA	—	7	Bilat	—
Khayat et al., 201914	45/F	Anaplastic ependymoma	—	9	Bilat	PT
Lana et al., 201815	70/M	Oligodendroglioma	Midline telovelar	3	Bilat	PT
McDonald et al., 202216	25/M	PA	—	3	Lt	PT
Schaller-Paule et al., 202111	20/F	PA	Paravermal	2	Rt	—
	60/F	PA	Paravermal	8	Rt	—
	32/M	PA	Paravermal	6	Lt	—
	35/M	Ependymoma	Midline telovelar	3	Lt	—
	34/M	Medulloblastoma	Midline telovelar	10	Bilat	—
	40/M	Medulloblastoma	Paravermal + telovelar	3	Rt	—
Schaller-Paule et al., 201917	26/M	Medulloblastoma	—	9	Bilat	—
	19/F	Medulloblastoma	Midline telovelar	8	Bilat	PT
	35/M	Medulloblastoma	Midline telovelar	10	Bilat	—
	41/M	Medulloblastoma	Midline telovelar	3	Rt	PT
Shinohara et al., 201310	57/F	Breast metastasis	—	1	Lt	—
	79/M	Lung metastasis	—	3	Rt	—
	41/F	Ependymoma	—	1	Bilat	—
	58/M	Brainstem glioma	—	1	Bilat	—
Vaidhyanath et al., 201018	57/M	Epidermoid cyst	—	6	Bilat	PT

PA = pilocytic astrocytoma; PT = palatal tremor; — = not available.

The characteristics of 23 adult patients with hypertrophic olivary degeneration (HOD) development after resection of midline posterior cranial fossa (PCF) tumors are shown. Surgery to diagnosis of HOD is defined as the length of time between tumor resection and discovery of inferior olivary nucleus (ION) hyperintensity on T2/FLAIR MR Iimaging.^10–18

Of the 23 patients who met our search criteria, the majority underwent resection of medulloblastoma (35%) or pilocytic astrocytoma (26%). The other cases involved rare gliomas, metastases, and one epidermoid cyst.¹⁸ HOD occurrence was bilateral in 57% (13/23) of these patients. No association was observed between surgical approach and whether the subsequent development of HOD was unilateral versus bilateral. Whether severity of symptoms was associated with bilateral versus unilateral HOD was a point of interest, yet no conclusion could be made on this topic due to the small sample size and lack of uniformity in reported symptoms. The effect of tumor extent on laterality was not investigated. The mean interval between resection and HOD identification on follow-up imaging was 4.6 months (range 0–10 months).

Discussion

Observations

We describe a case of HOD in an adult patient 4 months after resection of a low-grade vermal pilocytic astrocytoma. Characteristic symptoms of palatal tremor, ocular myoclonus, and ocular nystagmus were observed subtly at 2 months but progressed considerably by 4 months postresection. This temporal pattern of symptoms aligns with other reported cases. Palatal tremor is the most frequently reported symptom, present in 20%–45% of cases.¹,⁸,19 The gold standard for detecting this symptom is FEES, yet this diagnostic is not universal.¹¹ The ION hyperintensities in our case were bilateral, with no remote lesion specifically identified in the DROP. While the presence of such a lesion along the Guillain-Mollaret triangle strongly supports the diagnosis of HOD,⁷ it is absent in nearly half of HOD cases.¹ Thus, a high degree of clinical suspicion in concert with specific imaging findings remains the sole unifying diagnostic criterion.

The highest rates of HOD after resection of PCF tumors have been associated with a paravermal transcerebellar approach, as this particularly jeopardizes the dentate nucleus.¹¹ Conversely, midline, lateral, and supracerebellar approaches are less frequently associated with HOD.¹¹ Unfortunately, fewer than half of the relevant cases in our literature review reported a specific surgical approach. Those that did provide this information endorsed either midline telovelar (7/10) or paravermal (4/10) approaches, with 1 case including both. Thus, a strong knowledge of the locations of deep cerebellar nuclei in relation to a surgical target is likely important to limit the risk of HOD in neurosurgical patients. Additionally, gentle dissection of the tumor from the surrounding structures is strongly advised, yet further recommendations are limited due to the rarity of this condition.

Managing the symptoms of HOD, when present, is quite difficult due to a lack of treatment guidelines and available literature. Some therapeutic trials have been performed to address specific symptoms of HOD such as ocular nystagmus or palatal tremor, yet these demonstrated only variable success.^20–22 Some described the symptoms as self-limiting and potentially responsive to antiseizure medications such as valproate, carbamazepine, and clonazepam.²³ Botox injection of the tensor veli palatini muscle has also been proposed as a safe and minimally invasive option for palatal myoclonus.²⁴ Evidence for the efficacy of these treatments is limited, however. Additionally, limitations in sample size and the lack of uniformity in symptom description across case reports restrict the interpretation of our literature review. While further therapeutic exploration is necessary, the remarkably rare nature of symptomatic HOD presents a challenging area for future research.

Lessons

HOD represents a rare MRI finding appearing months after midline PCF tumor resection in adults. While cases are often asymptomatic, they can be associated with debilitating symptoms including palatal tremor, nystagmus, ataxia, and other ocular abnormalities, as seen in our patient. Disruption of the DROP pathway is frequently cited as a cause of HOD, making it an important diagnosis for neurosurgeons to identify when presented with its specific symptoms and radiographic findings. Prognosis is generally poor, as no standardized treatment regimen for these patients currently exists. Therapeutic trials aimed toward addressing the symptoms of HOD have shown mixed results and represent an important area of ongoing research.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Small, Strickland. Acquisition of data: Miller, Small, Strickland. Analysis and interpretation of data: Venegas, Miller, Small. Drafting the article: all authors. Critically revising the article: Small, Strickland. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Venegas. Study supervision: Strickland.

Correspondence

Joshua M. Venegas: Medical University of South Carolina, Charleston, SC. venegasj@musc.edu.