0609 Case 1

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C O M J U N E 2 0 0 9 C A S E 1

A 47-YEAR OLD MALE WITH A CEREBELLOPONTINE ANGLE

TUMORbpa_309 739..742

Klaus Bumm1; Abbas Agaimy2; Gerald Niedobitek2; Heinrich Iro1; Helmut Steinhart1

1 Department of O torhinolaryngology, University of Erlangen-Nuremberg, Germany2 Department of Pathology, University of Erlangen-Nuremberg, Germany

CLINICAL HISTORY AND IMAGINGSTUDIES

A 47-year-old male patient presented with a fluctuating hearing

impairment in his left ear over the past 5 years. Tinnitus or vertigo

was not observed. Audiometric analysis showed an inner ear deficit

of 50 dB between 1500 and 6000 kHz on the left side. Hearing in

the right ear was normal. The facial nerve was clinically and by

means of electrophysiological testing without pathological find-

ings. BEAP (brainstem evoked auditory potentials) revealed a

latency increase between J1 and J3 up to 2.5 ms for the left side,

whereas only 2.3 ms on the right side. MRI (magnetic resonance

imaging) scanning showed a tumor of the cerebellopontine angle in

the left inner auditory canal (IAC) of 1.2 x 0.7 x 0.9 cm in size(Figure 1). After application of contrast media, the tumor showed

clear signal enhancement.

The tumor was entirely removed by a transtemporal approach to

the IAC. Surgical exploration found the cochlear nerve embedded

in a tumorous mass, whereas the vestibular and the facial nerve

were normal (Figure 2a, vestibular nerve arrow A and cochlear

nerve with tumor arrow B).

Nerve and tumor (Figure 2b) were removed and sent to histo-

pathological examination. The patient lost his hearing after the

operation due to the removal of the cochlear nerve, whereas a

regular postoperative vestibular function was observed. The post-

operative course as well as the 5-year follow-up examination was

unremarkable and control MRI scanning showed no recurrence.

PATHOLOGIC FINDINGS

Histopathological examination revealed a tumor composed of

loosely packed irregular nerve fibres embedded within loose con-

nective tissue (Figure 3a, H&E-stain, x 100). Mature adipose tissue

elements and numerous capillary- to medium-sized thin-walled

vascular channels were diffusely dispersed between nerve fibres. In

addition, isolated adipocytes were seen within the endoneurium of some nerve fibres, but no skeletal muscle cells, ganglionic cells,

glial elements or other tissue derivatives were seen. Also, hemosid-

erin pigment, scarring or inflammatory cells as would be antici-

pated in amputation (traumatic) neuroma were not observed.

Immunohistochemistry revealed a strong expression of protein

S100 and neurofilament protein in the nerve axons and Schwann

cells (Figure. 3b, x 100). An intact perineurial sheath was high-

lighted by reactivity for epithelial membrane antigen (Figure 3c,

EMA).

Figure 1.

doi:10.1111/j.1750-3639.2009.00309.x

739Brain Pathology 19 (2009) 739–742

© 2009 The Authors; Journal Compilation © 2009 International Society of Neuropathology

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B

A

Figure 2.

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740 Brain Pathology 19 (2009) 739–742


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B

A

C

Figure 3.

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741Brain Pathology 19 (2009) 739–742


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DIAGNOSIS

Angiolipomatous hamartoma of the cochlear nerve

DISCUSSION

Most tumors of the cerebellopontine angle are schwannomas and

over 90% originate from the superior branch of the vestibular nerve. Tumors originating from the cochlear nerve are rare (1–3).

This case raises two major issues.The first one relates to the precise

allocation of the tumor to the affected nerve and the probable

histological diagnosis based on clinical and imaging findings. The

second issue concerns the pathogenesis of this peculiar lesion at

this unusual location.

The allocation of tumors to the cochlear nerve within the IAC is

most likely when they expand towards or even into the cochlea

(4–6). In this case there was no signal enhancement detectable

within the cochlea, so we did not presume a pathology arising

from the cochlear nerve. The only denominator was a progressive

hearing impairment, a non-specific symptom for cochlear nerve

involvement.After surgical exploration it became apparent that the

tumor was clearly originating from the cochlear nerve and associa-tion to the surrounding nerves could be excluded. This contrasts

with schwannomas of the vestibular nerve as they are known to

merge with surrounding nerves and therefore often hamper an easy

determination of their origin.

Since the majority of tumors originating in the IAC are schwan-

nomas, alternative diagnoses at this anatomic site seem quite

unusual. The histopathological differential diagnosis of our case

included traumatic neuroma, true circumscribed “palisaded”

neuroma, neuromuscular choristoma and lipomatous hamartoma

of the cochlear nerve. Schwannoma and neurofibroma could be

primarily excluded based on well defined criteria. Against a diag-

nosis of circumscribed neuroma argue the irregular borders of the

lesion and the prominent angiolipomatous component. Likewise,absence of a history of previous surgery or trauma of any kind, and

lacking of typical microfascicular pattern of traumatic neuroma as

well as signs of scarring, old bleeding and inflammatory cells pre-

clude a diagnosis of traumatic neuroma. A more plausible explana-

tion would be a non-traumatic “choristomatous” or “hamartoma-

tous” origin. In fact, the finely distributed adipocytic elements and

prominent vascular component represent a strong clue to the

choristomatous nature of the lesion. However, no skeletal muscle

fibers were seen, thus excluding a neuromuscular hamartoma

(choristoma) of cranial nerves.

Hamartomas of the IAC are exceedingly rare lesions and most

were described as case report or small series (7–9). Lesions

described by Wu et al (9) under the rubric of “lipochoristoma”

showed a heterogeneous histology, someof them contained skeletal

muscles and thus represent neuromuscular choristomas. Other rare

lesions described as lipomas of the IAC are probably lipomatous

hamartomas,as they were less circumscribed and lacked the encap-

sulation typical of true benign lipomatous tumors of the soft tissue.

However, given the finely dispersed fatty and vascular components

and absence of other tissue elements, we suggest the term “angioli-

pomatous hamartoma” for this peculiar lesion to alert to its high

vascularity that might suggest a more serious pathology onimaging procedures.

In summary, we described an unusual case that we believe to

represent the first description of an angiolipomatous hamartoma

of the cochlear nerve. The pathogenesis of this rare lesion at this

location remains unknown. Hamartomas should be included in

the pre-operative differential diagnosis of acoustic or vestibular

schwannoma.

REFERENCES

1. Brackmann DE, Bartels LJ (1980) Rare tumors of the cerebellopontine

angel. Otolaryngol Head Neck Surg 88:555–559.

2. Komatsuzaki A, Tsunoda A (2001) Nerve origin of the acoustic

neuroma. J Laryngol Otol 115:376–379.3. Alobid I, Gaston F, Morello A, Menendez LM, Benitez P (2002)

Cavernous hemangioma of the internal auditory canal. Acta

Otolaryngol 122:501–503.

4. Brogan M, Chakeres DW (1990) Gd-DTPA-enahanced MR imaging of

cochlear schwannoma. AJNR 11:407–408.

5. Gersdorff MC, Decat M, Duprez T, Deggouj N (1996) Intracochlear

schwannoma. Eur Arch Otorhinolaryngol 253:374–376.

6. Neff BA, Willcox TO, Sataloff RT (2003) Intralabyrinthine

schwannomas. Otol Neurotol 24:299–307.

7. Matthies C, Osorio E, Samii M (2003) Hamartomas of the internal

auditory canal: report of two cases. Carvalho GA, Neurosurgery

52:944–948.

8. Karagama YG, Bridges LR, van Hille PT (2002) Neuromuscular

hamartoma of the cochlear nerve: a rare occurrence in the internal

auditory meatus. Eur Arch Otorhinolaryngol 259:119–120.9. Wu SS, Lo WW, Tschirhart DL, Slattery WH 3rd, Carberry JN,

Brackmann DE (2003) Lipochoristomas (lipomatous tumors) of the

acoustic nerve. Arch Pathol Lab Med 127:1475–9.

ABSTRACT

A 47-year old man presented with a five-year history of fluctuating

hearing impairment in the left ear. There was no tinnitus or vertigo.

Imaging studies demonstrated a contrast-enhancing cerebellopon-

tine angle mass in the left internal auditory canal. Surgically the

lesion was attached to the cochlear nerve. Pathological evaluation

revealed what is best described as an angiolipomatous hamartoma

of the cochlear nerve. Similar lesions have only rarely been

described.

Correspondence

742 Brain Pathology 19 (2009) 739–742


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0609 Case 1