Background: Meningioma is one of the most common intracranial tumors with well-established radiologic
features such as contrast enhancement, dural tail, and hyperostosis on computed tomography
and magnetic resonance imaging. Meningiomas enhance avidly on contrast-weighted images
based on the tumor vascularity or underlying histopathology except for areas of necrosis
or cyst. Even in this context, faint or nonenhancing meningioma is exceedingly rare.
We are presenting a rare case of a patient with a nonenhancing meningioma in the cranial
base with neither radiological features of cystic changes nor necrosis. The implication
of the enhancement on pathological features and clinical outcomes is not known. A
systematic review was performed to analyze minimal or nonenhancing meningioma with
regard to tumor location, histological type, and prognosis.
Case Description and Imaging: A 57-year-old male presented with progressive right hearing loss, disequilibrium,
occasional difficulty swallowing, and facial numbness. Noncontrast CT of the head
revealed a hypodense right cerebellopontine angle mass extending from the interpeduncular
and ambient cisterns to the foramen magnum ([Fig. 1A and B]). Magnetic resonance imaging showed a 5.2 cm × 3.8 cm × 5.5 cm (anteroposterior × lateral × craniocaudal)
T1-weighted hypointense and T2-weighted hyperintense mass ([Fig. 1C and D]). The three-dimension fast imaging employing steady-state acquisition (FIESTA) sequence
revealed the tumor also extended into the right internal acoustic canal (IAC, [Fig. E]) and Meckel's cave. The mass displayed an intermediate diffusion signal when compared
with adjacent CSF ([Fig. 1F]). Gadoterate meglumine contrast injection did not reveal an apparent enhancement.
There was a faint enhancement around the tentorium but no significant enhancement
within the tumor ([Fig. 1G]).
Operative Procedure and Histopathological Analysis: The patient underwent a posterior petrosal approach for tumor resection ([Fig. 2]). The tumor stained for vimentin, GFAP, and Cyclin D1, with low Ki-67 (<2%), and with an epithelioid reticulin pattern ([Fig. 3]). The pathological analysis demonstrated a microcystic meningioma WHO grade I.
Systematic Review: Seven articles, including case reports and case series, had 14 verifiable cases included
in the systemic review1–7. The average age was 48.1 years, and the majority were female
(71.4%). Convexity meningioma was the common location at 57.1%. Two cases involved
the skull base, and one case involved the lumbosacral region. All cases included a
faint or nonenhancing meningioma. Microcystic meningioma was the most common histological
type at 85.7% (12/14). Clear cell and fibrous meningioma were other histological types
of nonenhancing meningioma, respectively. Two patients had radiotherapy for adjuvant
treatment.
Discussion: Meningioma presented in this case lacked the typical features associated with the
tumor including contrast enhancement, hyperostosis, and dural tail. The absence of
these signs rendered meningioma as an unlikely diagnosis. However, the histopathology
analysis indicated microcystic meningioma. The literature review indicated that the
majority of unenhanced meningioma had microcystic histopathology. However, only 10.2%
of microcystic meningiomas are nonenhancing.
Conclusion: Meningioma should be considered as a rare differential diagnosis for a nonenhancing
lesion at the cerebellopontine and petroclival regions.
Fig. 1
Fig. 2
Fig. 3 (A) H&E stain (×4), (B) vimentin, (C) cyclin-D, (D) reticulin, (E) GFAP, (F) Ki-67. H&E, hematoxylin and eosin.
