Jeanne D Keller

John R Knorr

Robin I Davidson

Ronald L Ragland

Thomas W Smith

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1182 
Squamous Carcinoma Arising in a Cerebellopontine Angle 
Epidermoid: CT and MR Findings 
John R. Knorr, 1 Ronald L. Ragland ,1 Thomas W. Smith,2 Robin I. Davidson,3 and Jeanne D. Keller1 
Intracranial epidermoid tumors are rare lesions, which re-
portedly account for less than 1% of intracranial tumors that 
arise as a result of the inclusion of squamous epithelium 
during embryogenesis [1]. This report describes the CT and 
MR findings of the rarer occurrence of a squamous cell 
carcinoma arising in a cerebellopontine angle epidermoid and 
extending into the cerebellum. 
Case Report 
A 74-year-old man presented at another outside institution with 
vertigo, nausea, and vomiting . A CT examination of the head was 
reported to show a low-density, roughly spherical mass in the region 
of the left cerebellopontine angle. There was some peripheral high 
density, suggestive of an irregular, calcified component. MR con-
firmed the extraaxial location of the lesion and it was thought to be 
consistent with an epidermoid. On angiography, the lesion was 
avascular. A left suboccipital craniotomy revealed a pearly white 
lesion, typical of a benign epidermoid adherent to the arachnoid of 
the left cerebellar hemisphere. The aspirated fluid was yellowish and 
oily. No intraaxial extension was present. Pathologically, a benign 
epidermoid cyst with pseudostratified squamous epithelium was di-
agnosed. 
The patient did well until 13 months later, when he experienced 
headaches, ataxia, confusion , nausea, and vomiting . Repeat CT 
examination revealed a 3-cm recurrent hypodense lesion with an 
irregular rim of enhancement. There was resultant obstructive hydro-
cephalus. A ventriculostomy was performed, at which time an ex-
traaxial cystic lesion extending inferiorly to the left cerebellar tonsil 
was noted. Because of the adherent nature of the cyst wall, it could 
not be totally removed . 
Pathologic inspection revealed a moderately differentiated squa-
mous cell carcinoma consisting of cells with large hyperchromatic 
nuclei, nuclear folding, rare mitoses, and occasional squamous pearls 
(Fig . 1A). In some areas a transition between dysplastic squamous 
epithelium lining a cyst wall and overt carcinoma was apparent. 
Two months later, the patient was admitted to our institution with 
ataxia, nausea, and vomiting . Contrast-enhanced CT scans (GE 9800 
Quick, Milwaukee) revealed an enhancing lesion with irregular borders 
and postoperative changes (Figs. 1 B and 1 C). The mass displaced 
the fourth ventricle to the right. The center of the mass did not 
enhance. T1-weighted MR examination (600/20/1) (Signa, 1.5 T, 
General Electric, Milwaukee) revealed evidence of prior surgery and 
a hypointense mass in the posterior fossa. The T2-weighted (2250/ 
80/1) images showed extensive edema and a cystic component. 
Gadopentetate-dimeglumine-enhanced T1-weighted (600/20/1) im-
ages outlined a heterogeneously enhancing mass with irregular, 
crumpled margins (Figs. 1 D-1 F). 
A third debulking was performed. Pathologic examination of the 
tissue removed again showed poorly differentiated squamous carci-
noma with markedly anaplastic cells and many mitotic figures (Fig . 
1 G). Radiation therapy was begun; however, the patient died 7 weeks 
after admission. A postmortem examination, limited to the posterior 
fossa, revealed an extensive tumor infiltrating the left cerebellum and 
extending across the midline. 
Discussion 
This case represents the unusual occurrence of malignant 
transformation in an epidermoid [2]. Such changes have been 
reported at postmortem examinations [3) . In 1960 Davidson 
and Small [4] described a case in which malignancy was 
diagnosed in a living patient. Nasaki et al. [5] described such 
a tumor visualized by CT. In our case the lesion was identified 
on both CT and MR. 
Of the cases previously reported, 13 were male patients 
and seven were female, a similar male predominance to that 
seen in benign epidermoid [6]. The age peak for malignant 
transformation is also similar to that for epidermoid tumor 
occurrence [7]. The 13-month period of apparent malignant 
transformation in our patient was rather short: the longest 
reported period between epidermoid resection and detection 
of malignancy is 33 years [2]. Malignant tumor location is 
most common in the parapontine areas (five cases), parapi-
tuitaryjbasal (four cases), frontal (four cases), cerebellopon-
tine angle (four cases), fourth ventricle (two cases), sella 
turcica (one case), and parietooccipital region (one case) [7]. 
Because of the central location of the tumor, obstructive 
hydrocephalus is a frequent problem. The complex pattern of 
tumor growth and the insinuation in and around neurovascular 
structures make total resection difficult [8]. 
Received February 5, 1991; revision requested March 29, 1991; revision received May 15, 1991; accepted May 20, 1991. 
' Department of Radiology, University of Massachusetts Medical Center, 55 Lake Ave., N. , Worcester, MA 01655. Address reprint requests to J. R. Knorr. 
2 Department of Neuropathology, University of Massachusetts Medical Center, Worcester, MA 01655. 
3 Department of Neurosurgery, University of Massachusetts Medical Center, Worcester, MA 01655. 
AJNR 12: 1182- 1184, November /December 1991 0195- 61 08/91/1206-11 82 © American Society of Neuroradiology 
AJNR:12, November/December 1991 MALIGNANT TRANSFORMATION OF EPIDERMOID 
A 8 
D E 
Fig. 1.-74-year-old man with malignant transformation of epidermoid tumor. 
A, Photomicrograph of stained specimen obtained during second operation reveals a moderately 
differentiated squamous cell carcinoma. Large hyperchromatic nuclei (arrows) with nuclear folding, 
rare mitosis, and squamous pearl (arrowheads) are present. (Hand E, original magnification x120) 
B and C, Pre· (8) and post- (C) contrast-enhanced CT scans obtained before third operation 
reveal large left cerebellar mass displacing fourth ventricle. Irregular, ringlike enhancement and 
adjacent craniotomy changes are seen. 
D, Precontrast T2-weighted (2250/80/1) MR image obtained before third operation (degraded by 
patient motion) shows the heterogeneously increased signal with adjacent edema in the left 
cerebellar hemisphere. 
E, Precontrast sagittal T1-weighted (600/20/1) MR image reveals evidence of previous surgery 
and hypointense mass in left cerebellum. 
F, Contrast-enhanced T1-weighted (600/20/1) MR image reveals a heterogeneously enhancing 
left cerebellar lesion with irregular borders. The lesion appears to be intraaxial. 
G, Photomicrograph of stained specimen obtained during third operation reveals poorly differen-
tiated squamous carcinoma with markedly anaplastic cells (arrows) and many mitotic figures. (Hand 
E, original magnification x 120) 
c 
F 
G 
1183 
The clinical outcome in patients with intracranial squamous 
carcinoma degeneration is bleaker than that in cases of benign 
epidermoids. Only one patient has been reported to have lived 
3 years after documentation of malignancy [2] . This differs 
from the generally good prognosis for benign epidermoids 
reported by Yamakawa et al. [6] . Although 24% of their 
patients had recurrence, the average interval was almost nine 
years. If a second occurrence was discovered, the average 
interval was another 12112 years. The 20-year survival rate 
was approximately 93%. 
1184 KNORR ET AL. AJNR :12, November/December 1991 
Postcontrast CT examination just prior to the discovery of 
carcinoma in our case displayed ring enhancement, a rare 
occurrence in benign epidermoids [9]. Enhancement in path-
ologically benign tumors has been attributed to peritumoral 
granulation [1 0]. However, Lewis et al. [7] correlated more 
irregular CT enhancement with malignancy. In our case, the 
irregular nodular rim enhancement represented an area of 
malignancy. 
MR appearance of benign epidermoids has been well doc-
umented [9, 11, 12). The generally accepted pattern of low 
signal intensity on T1-weighted images and high intensity on 
T2-weighted images was investigated by Horowitz et al. [9], 
who described two subtypes of epidermoids: black and white, 
with low intensity on T1-weighted scans and high intensity on 
T2-weighted scans, respectively . Black epidermoids were 
found to have lower lipid content. The enhancement seen on 
MR images is due to the breakdown in the blood-brain barrier 
like that seen on CT with iodinated contrast infusion [13). 
Finally, because of its multiplanar capability, MR is better able 
than CT to define tumor extent [14]. 
Epidermoid tumors are uncommon intracranial lesions and 
secondary carcinomatous transformation is unusual. Malig-
nant change must be considered when a recurrent lesion 
shows intense enhancement, either on postcontrast CT or 
MR examination . 
ACKNOWLEDGMENT 
The authors gratefully acknowledge Kathy Delongchamp's tech-
nical assistance. 
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1989;1 0:351-356 
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3. Ernst P. Haufung Dysontogenetischer Bildunger am Zentralnervensys-
tems. Verh Disch Ges Pathol1912;15:226-230 
4. Davidson Sl, Small JM. Malignant change in a intracranial epidermoid. J 
Neural Neurosurg Psychiatry 1960;23 : 176-178 
5. Nasaki Y, Nagao S, Tabuchi K, Nishimoto R. Primary intracranial epider-
moid carcinoma. J Neurosurg 1979;50 :830-833 
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11 . Vion-Dury J, Vincentelli F, Jiddane M, et al. MR imaging of epidermoid 
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Squamous Carcinoma Arising in a Cerebellopontine Angle Epidermoid: CT and MR Findings

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Squamous Carcinoma Arising in a Cerebellopontine Angle Epidermoid: CT and MR Findings

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