CLINICAL CASE REVIEWSPONSORED BY GUERBET

Atypical Teratoid Rhabdoid Tumorof the Oculomotor Nerve
Aashim Bhatia, M.D., M.S.
Assistant Professor in Radiology
Pediatric Neuroradiologist/Pediatric Radiologist
Director of Academic Affairs, Radiology Department
Children’s Hospital of Pittsburgh of UPMC

Case Summary
An 8-year-old female with a history of attention deficit hyperactivity disorder, expressive language disorder,strabismus, and developmental delay. Patient initiallypresented to the emergency department with the following symptoms including restricted left eye movements (cranial nerve III palsy), ptosis, vomiting, and a
1-day history of headache. Initial magnetic resonanceimaging (MRI) demonstrated a mass along the left
oculomotor nerve (CN III), which was concerning for aschwannoma. The patient was discharged and scheduled for follow-up with ophthalmology and neurosurgery. The girl’s ptosis worsened, and she presented tothe emergency department 3 weeks later, when a follow-up MRI revealed enlargement of the mass despite
steroid treatment. A follow-up MRI at 4 weeks again
revealed continued enlargement of the mass, and thepatient underwent surgical resection of the mass.

Imaging Findings
Initial MRI demonstrated a mass involving the cisternal segment of the left oculomotor nerve (CN III) inthe midbrain (Figure 1). The mass demonstrated diffuse
enhancement following intravenous administration of agadolinium-based contrast agent (GBCA). The mass also
correlated with areas of reduced diffusion on diffusionweighted imaging (DWI). Follow-up MRI revealed continuing enlargement of the same mass, as well diffuse
enhancement, and areas of reduced diffusion at 3 andn©

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4 weeks after presentation. There were no additional
masses or abnormal leptomeningeal enhancement andthe remainder of the brain and orbits appeared normalon MRI.

Diagnosis
Atypical teratoid/ rhabdoid tumor (ATRT; WHO IV)

Discussion
Atypical teratoid/ rhabdoid tumor is listed in theembryonal group on the most recent WHO 2016 classification of CNS tumors and is defined by alterations ineither the INI1 gene or the rarer BRG1 gene.1 The tumor
most commonly appears before age 3 years, with amedian age of 24 months at diagnosis. Most have been
described in the posterior fossa, including the brainstem; however, ATRT can present supratentorial andeven as extra-renal rhabdoid tumors outside the central
nervous system.2,3 This case describes an atypical location involving the oculomotor nerve (CN III).
There are three molecular subtypes of ATRT (sonichedgehog [SHH)], TYR, and MYC), each having different
behavioral and clinical characteristics.4 ATRT can also
express ASCL1, a regulator of NOTCH signaling, which
is more common in the SHH subtype and is correlatedwith supratentorial location and an improved 5-year
overall survival.
MRI findings of ATRT classically describe a mass
with reduced diffusion, heterogeneous to homogeneous

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CLINICAL CASE REVIEWBDC

FIGURE 1. An 8-year-old female initially presents with ptosis and vomiting. MRI demonstrates mass (arrows) along the left oculomotor nerve
and involving the midbrain on the (A) CISS sequence (A), with the massdemonstrating reduced diffusion on the DWI and correlative ADC map(B, C) and diffuse enhancement on T1 postcontrast GBCA imaging (D).

enhancement, and necrosis. ATRT is similar to medulloblastoma on imaging; however, ATRT typically affects ayounger age group. Metastatic disease is common andfound in up to 25% of patients at initial presentation.
MR spectroscopy has shown promise in predicting
the molecular subtypes, which can help predict therapeutic response. A higher Cr/Cho ratio and ml/Cho ratio in
subtype 1 may correlate with the SHH subtype and ASCL1

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expression. The ASCL1 is associated with the NOTCHtarget, which provides a favorable therapeutic target.
Cases of ATRT involving the oculomotor nerve areextremely rare.2 The similarity of this case to those inthe literature is not only in the mass (involving CN III
and showing diffuse enhancement after GBCA administration and areas of reduced diffusion), but also in theclinical presentation of ptosis and CN III palsy. Other©

APPLIED RADIOLOGYnCLINICAL CASE REVIEWASPONSORED BY GUERBETBFIGURE 2. Four weeks after initial presentation and imaging, MRI demonstrated interval increase in size of the enhancing mass (A, arrow) on T1
postcontrast GBCA imaging, with enlarging areas of reduced diffusion on
DWI (B, arrow).

masses that can involve CN III include schwannomas
and low-grade gliomas, which do not commonly display
reduced diffusion. Obtaining thin slice, postcontrast
MRI sequences of a mass is important for further characterization and evaluation of leptomeningeal spreadand postcontrast spine imaging for metastatic disease.
Balanced steady-state free precession (b-SSFP)
sequences, such as constructive interference insteady-state (CISS) and fast imaging employing steadystate acquisition with phase cycling (FIESTa–c), permit
high spatial resolution and high cerebrospinal fluid-tosoft tissue contrast.5 The b-SSFP sequences enableaccurate detection of masses along cranial nerves;these masses can easily be missed, owing to theirsmall size and challenging location within CSF, whereother sequences can produce CSF flow artifacts.

Conclusion
A mass involving the oculomotor nerve displaying
enhancement and reduced diffusion on MRI in thepediatric population (especially 3 years or younger)n©

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should include ATRT in the differential. ATRT is a highgrade tumor that can present in atypical locations.
Familiarity with these atypical presentations can aid
neuroradiologists in making an accurate diagnosis.

References
1. Louis DN, Perry A, Reifenberger G, et al. The 2016 World Health Organization Classification of Tumors of the Central Nervous System: a summary.
Acta Neuropathol. 2016;131(6):1-18. doi:10.1007/s00401-016-1545-1
2. Oh, C. C., Orr, B. A., Bernardi, B., Garré, M. L., Rossi, A., Figà-Talamanca, L.,
Robinson, G. W., & Patay, Z. (2015). Atypical teratoid/rhabdoid tumor (ATRT)
arising from the 3rd cranial nerve in infants: a clinical-radiological entity?. JNeurooncol, 124(2), 175–183. https://doi.org/10.1007/s11060-015-1787-0.
3. Lee IH, Yoo SY, Kim JH, et al. Atypical teratoid/rhabdoid tumors of the central nervous system: imaging and clinical findings in 16 children. Clin Radiol.
2009;64(3):256-264. doi:10.1016/j.crad.2008.09.007
4. Ho B, Johann PD, Johann PD, et al. Molecular subgrouping of atypicalteratoid/rhabdoid tumors - A reinvestigation and current consensus. NeuroOncol. 2020;22(5):613-624. doi:10.1093/neuonc/noz235
5. Li Z, Chen YA, Chow D, Talbott J, Glastonbury C, Shah V. Practical applications of CISS MRI in spine imaging. Eur J Radiol Open. 2019;6(May):231-242.
doi:10.1016/j.ejro.2019.06.001

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