- Email: [email protected]
Cerebellopontine angle lipoma
134
Surg Neurol 1985;23:134-8
Cerebellopontine Angle Lipoma Shelley B. Rosenbloom, M.D., Benjamin S. Carson, M.D., Henry Wang, M.D., Arthur E. Rosenbaum, M.D., and George B. Udvarhelyi, M.D. Departments of Neuroradiology and Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
Lipomas rarely occur intracranially. Moreover, the cerebellopontine angle is one of the more unusual sites of such hamartomas. Of the 11 reported cases, all but three caused symptoms related to compression of the cranial nerves in the cerebellopontine angle. Only three separate cases have been studied by computed tomography, and in one the fat density was not recognized. This report deals with the clinical presentations, surgical management, and radiologic assessment of these lesions.
1) matching the density o f the orbital fat. N o enhancement was detected. The fourth ventricle was in the midline; the lack of mass effect on the ventricle suggested a soft tumor. The internal auditory canals were symmetric and there was no erosion of bone (Figure 2). Coronal and sagittal computer reconstructions demonstrated that the lesion was confined to the infratentorial compartment and abutted the posterior wall of the petrous ridge (Figures 3 and 4). Left vertebral angiography was unremarkable except for possible medial displacement of the left anterior inferior cerebellar artery.
KEY WORDS: Cerebellopontine angle tumor; Lipoma; Computed tomography; Differential diagnosis; Radiologic assessment; Surgical management
Surgery
Rosenbloom SB, Carson BS, Wang H, Rosenbaum AE, Udvarhelyi GB. Cerebellopontine angle lipoma. Surg Neurol 1985;23:134-8.
Clinical Presentation A 28-year-old man presented with chronic left-sided dull and persistent supraorbital and maxillary headaches. H e had had episodes of nausea and dizziness for 1 year. T h e r e was no history of hearing loss. Physical examination disclosed minimal left ptosis and sensory impairment in the ophthalmic and mandibular distribution of the fifth cranial nerve on the left side of the face. The left pupil was slightly smaller than the right, but both reacted normally to light and on accommodation. The neurological examination was otherwise unremarkable, including auditory and cerebellar functions. Laboratory auditory and vestibular testing showed a partial paralysis of the left semicircular canal vestibular reflex. Radiologic Assessment Computed tomography (CT) scans performed before and after intravenous enhancement demonstrated a hypodense lesion in the left cerebellopontine angle (Figure
Utilizing the park bench position, a left paramastoidsuboccipital craniectomy was performed. A yellow mass the size o f a large walnut was immediately identified in the cerebellopontine angle as the left cerebellar hemisphere was retracted medially. The tumor incorporated portions of seventh, eighth, and ninth cranial nerves and was juxtaposed to the postero-superior aspect of the trigeminal nerve (first and second divisions) producing some displacement of these structures (Figure 5). The tumor was surgically separated from the fifth nerve and debulked, but intrinsic fibrous septa, abundant blood vessels, and adherence to the cranial nerves and brainstem precluded total resection. During the surgical manipulation, the eighth nerve, which merged with the lesion, became more attenuated. A pathological report of fibroadipose tissue consistent with lipoma was returned. The patient did well postoperatively with complete alleviation of head and facial pain. Subsequently, he experienced a significant decline in left auditory function and eventually developed some recurrent dizziness.
Discussion
Incidence Address reprint requests to: George B. Udvarhelyi, M.D., Johns
Hopkins Medical Institutions, Hampton House 255, 624 N. Broadway, Baltimore, Maryland 21205. © 1985 by ElsevierSciencePublishing Co., Inc.
Intracranial lipomas are rare lesions in both autopsy and CT experience. Vonderahe et al [ 13] reported 4 among 0090-3019/85/$3.30
Cerebellopontine Angle Lipoma
Surg Neurol 1985;23:134-8
135
Figure 3. Sagittally reconstructed image at the level of the anterior clinoid demonstrates the opposition of the lipoma to the posterior aspect of the petrous ridge.
Figure 1. Reversed axial C T image at the level of the internal auditory canals demonstrates a fat-density lesion lying in the cerebellopontine angle cistern. The lesion has remarkably little mass effect for its size: there is no apparent displacement of the tonsils or vallecula. 5000 autopsies. In neuropathological autopsy series, their influence is higher (9 in 1956 tumor cases from 4290 neurosurgical autopsies) [1]. Kazner et al [5] reported only 11 from 17,500 CT examinations. Zimmerman et Figure 2. Wide-windowed C T image demonstrates no evidence of bone erosion of internal auditory canal asymmetry.
al [15] found 10 cases among 700 intracranial tumors diagnosed by CT scans (1.3%). Most intracranial lipomas occur in the pericallosal cistern and may be associated with other cerebral malformations, particularly hypoplasia of the corpus callosum [10]. Krainer's series [7] lists the following additional characteristic locations for lipoma: ambient and quadrigeminal cisterns, interpeduncular fossa cisterns, suprasellar and perihypophyseal cisterns, olfactory cistern, sylvian cistern, cerebellopontine angle cistern, cisterna magna, tela choroidea of the lateral and third ventricles, their choroid plexus, and associated cisternal vela. Whereas lipoma of the pericallosal cistern is frequently associated with neurological abnormalities (especially convulsive seizures), these may be attributed to associated dysgenetic abnormalities (heterotopias, microcephaly, polymicrogyria, etc.). Pericallosal cistern lipomas have been discovered in neurologically normal people (e.g., Budkha [1] case 11). Nonetheless, with the ex-
Figure 4. Coronal computed reconstruction demonstrates that the lesion is entirely infratentorial and immediate(~ adjacent to the medial aspect of the petrous ridge. ~..... ~ii¸
. ~i~i ~ i!~ ¸¸~¸
7ii!¸~¸¸
~
~!
136
Surg Neurol 1985 ;23:134-8
Rosenbloom et al
Figure 5. Intraoperative photograph. T = tumor; C = cerebellum; arrow =attenuated 7th and 8th nerves; asterisk = lower cranial nerves; note branches of antero-inferior cerebellar artery above the tumor and impingement of the superior-medial portion of the tumor on the 5 th cranial nerve.
ception of pericallosal cistern lipoma, intracranial lipomas are usually incidental findings and are not associated with neurological symptoms unless they produce hydrocephalus. Cerebellopontine angle lesions have a higher incidence o f focal neurologic findings (especially eighth nerve dysfunction) than other intracranial lipomas (except pericallosal cistern lipomas). At least 9 of 12 were symptomatic (Table 1). These lesions occur predominantly on the left (10 of 12 cases) and in males (9 of 12 cases). T h e age o f presentation also varies widely, 17 months [2] to 77 years [ 1], with no distinguishable peak.
Radiologic
Differential
Diagnosis
Prior to CT scanning, no useful method for differentiating lipoma preoperatively from other cerebellopontine angle masses was available. Radiographic studies have sh~own enlargement o f the internal auditory canal, characteristic o f acoustic neuromas, in four lipomas [3,9,14]. Symmetric internal auditory canals are reported in one previous case [8]. Cisternography (iodinated contrast or gas) is reported in five cases. Nonfilling o f the internal auditory canal, cisternal mass, or cisternal obliteration (Fukui) was shown in all o f these [3,8,9,14], although the mass was not detected on an
initial study in one case [9]. Vertebral angiography has been reported as unremarkable or showing only mass effect in two cases [4,8]. In one patient, a dilated, tortuous distal anterior-inferior cerebellar artery, ipsilateral to the lesion, was described [3]. Computed tomography studies of cerebellopontine angle lipomas have been reported in this and in three previous cases [2,4,8]. In the single negative CT study [8], an ~ 11-mm tumor was discovered surgically. The type of CT scanner and quality of the CT examination are not described. Lipomas o f the cerebellopontine angle have been identified on CT previously in two cases. Faerber and Wolpert [2] demonstrated a very large, fatdensity tumor extending into the middle fossa from the cerebellopontine angle. N o surgical confirmation is available in this case. Graves and Schemm [4] demonstrated a 1.5-cm tumor measuring - 2 5 to - 4 5 Hounsfield units which was operated upon and confirmed. The present case appears to be the first examined with a highresolution x-ray CT unit (Siemens DR3). Although the CT appearance of the cerebellopontine angle lipoma is characteristic, there are differential considerations. Low-density lesions of the cerebellopontine angle include: cystic acoustic neuromas, cystic or fatty meningiomas, epidermoids, arachnoid cysts, cystic or necrotic metastases, and dermoids (see Table 2). Nonlipomatous fatty tumors such as hibernomas do not seem to appear in the cerebellopontine angle. Acoustic neuroma, by far the commonest cerebellopontine angle tumor, characteristically demonstrates CT numbers higher than those of fat and usually brighter on intravenous enhancement. Most cause widening of the internal auditory canal. Meningiomas, the second most common masses in the cerebellopontine angle, are usually hypodense lesions. When necrotic or cystic, they may appear hypodense, but usually heterogeneously so, and are associated with at least minimal intravenous enhancement. The CT numbers are characteristically higher than those of fat. Lipomatous infiltration was demonstrated histologically in 5% or 6 of 131 consecutive meningiomas reviewed by Russell et al [11]. The CT appearance of these tumors was atypical in four cases, but none was sufficiently hypodense to suggest a fatty component on CT. The third most common cerebellopontine angle tumor, epidermoid, may also present as a low-density lesion on CT. In the report by Zimmerman et al [15], of 27 intracranial tumors o f maldevelopmental origin (12 lipomas, 10 epidermoids, 4 dermoids, and 1 teratoma), intracranial fat was detectable by low CT number in lipomas, dermoids, and the teratoma, but not in their cases of epidermoid. Only 3 of 35 dermoids were described as partially fatty in combining several series. Epidermoids were of cerebrospinal fluid equivalent den-
C e r e b e l l o p o n t i n e A n g l e Lipoma
T a b l e 1.
Surg N e u r o l 1985;23:134-8
137
Clinical Features of CerebellopontineAngle Lipoma
Source
Age/sex
l. Klob [6] (1859)
Autopsy or surgical
M
2. Stefan [12] (1933)
40/F
A
3. Budka [1] (1974)
77/M
A
4. Budka [1] (1974)
26/F
5. Faerber [2] (1976)
17 mos/M
Symptoms
Radiographic findings
Bright's disease 8th nerve dysfunction TB meningitis No pertinent clinical symptoms Head trauma
Pathology Fatty tumor Olive-sized lesion Fat cells infiltrating meninges Calcification in adjacent brain Hypertrophy of nerves within the tumor Plaque of mixed tissue in pontine gray matter Lipomatous infiltration of 8th
5th and 8th nerve dysfunction
nerv~2
CT: Fatty tumor extending from CPA to suprasellar cistern Skull x-ray: bone erosion Vertebral angio: dilated AICA PEG: L CPA tumor PEG: L CPA tumor
Not described
6. Fukui [3] (1977)
28/F
S
8th nerve dysfunction
7. Winther [ 14] (1978)
50/M
S
8th nerve dysfunction
8. Olson [9] (1978)
42/M
S
TB meningitis 8th nerve dysfunction
Polytome: bone erosion Posterior fossa myelogram
None
Thinly encapsulated tumor attached to arachnoid of left cerebellar hemisphere and brainstem Fatty tumor infiltrating 7th to 10th cranial nerves with a thin capsule laterally but not medially. Adherent brainstem Unencapsulated 7.5-mm tumor
Abbreviations: CPA - cerebellopontine angle; PEG - pneumoencephalogram; L - left; AICA = antero-inferior cerebellar artery.
sity i n 9 o f 2 0 l e s i o n s [ 1 5 ] a n d i n 17 o f 2 5 c a s e s i n t h e literature. Two were partially calcified; their hypodensity w a s a t t r i b u t e d t o a d m i x t u r e o f h y p e r d e n s e k e r a t i n -
T a b l e 2.
ized, proteinaceous debris and hypodense cholesterin (with or without calcification) due to saponification. A r a c h n o i d cysts a r e usually c o n s i d e r e d t h e f o u r t h m o s t
Computed Tomography of Hypodense CerebellopontineAngle Lesions."Differential Diagnosis C T Density
Fat Content
Calcium
Enhancement
Effect on Bone
Acoustic schwannoma Meningioma
Heterogeneous; usually isodense Usually hyperdense
None
Uncommon
Usually present
Rare
Frequent
Usually present
Epidermoid
Usually CSF density; may be heterogeneous; thin wall usually Usually CSF density; thin wall Usually mixed density; thick wall usually
Seen in 3 of 35 cases on CT None
Seen in 2 of 35 cases
Not present
Erodes IAC; may erode petrous ridge May produce hyperostosis; erosion unusual May erode bone
None
Not present
May erode bone
Not present
May be associated with transcalvarial sinus tract
Cystic or necrotic lesions usually have thick, nodular walls Fatty; uniform
None
In 6 of 9 cases reported may be dental elements Rare
Present
May erode bone
Present
Not reported
None
May erode bone (4 of 6 cases)
Arachnoid cyst Dermoid
Metastasis
Lipoma
Partially fatty in 3 of 4 cases
Abbreviations: CT = computed tomography; 1AC = internal auditory canal.
138
Surg N e u r o l 1985;23:134-8
common cerebellopontine angle tumor. Characteristically of cerebrospinal fluid density, they may occasionally be slightly denser and may remodel the adjacent bone. Fatty components or calcification are not concomitants. Dermoid tumors are rare in the cerebellopontine angle and tend to occur in the midline. Calcification on CT scanning was noted in six of nine cases [15] and ectodermal and mesodermal elements (hair, sebaceous glands, apocrine glands) contributed to the focal hypodensity of"fat" on CT [15]. The heterogeneous density of these lesions and their rarity beyond the midline aid the diagnostician. Summary Cerebellopontine angle lipomas are rare. Characteristics for consideration in the differential diagnosis of hypodense lesions on x-ray CT scanning were discussed. The clinical presentation of these lesions is characteristic of a cerebellopontine angle mass. Their excision is difficult because of adherence to cranial nerves and the brainstem and infiltration of blood vessels. The surgical objectives are often limited to decompression even using the operating microscope.
R o s e n b l o o m et al
3. 4.
5.
6. 7. 8.
9. 10. 11.
12.
13. 14.
References 1. Budka H. Intracranial lipomatous hamartomas (intracranial "lipomas"). Acta Neuropathol (Berl) 1974;28:205-22. 2. Faerber EN, Wolpert SM. The value of computed tomography
15.
in the diagnosis of intracranial lipoma. J Comput Assist Tomogr 1978;2:297-9. Fukui M, Tonaka A, Kitamura K, Okudera T. Lipoma of the cerebellopontine angle. Case report. J Neurosurg 1977;46:544-7. Graves VB, Schemm GW. Clinical characteristics and CT findings in lipoma of the cerebellopontine angle. Case report. J Neurosurg 1982;57:839-41. Kazner E, Stochdorph O, Wende S, Grumme T. Intracranial lipoma. Diagnostic and therapeutic considerations. J Neurosurg 1980;52:234-45. KlobJ. Zur Pathologie der Fettgeschwulste. Z Gesell Arzte Wien 1859;673-45. Krainer L. Die Hirn- und Ruckenmarkslipome. Virchows Arch Pathol Anat 1935;295:107-42. Mattern WC, Blatmer RE, WerthJ, Shuman R, Block S, Liebrock LG. Eighth nerve lipoma. Case report. J Neurosurg 1980;53:397400. Olson JE, Glassock ME, Britton BH. Lipomas of the internal auditory canal. Acta Otolaryngol 1978:104:431-6. Russell DS, Rubinstein LJ. Pathology of the nervous system. 2nd ed. Baltimore: Williams & Wilkins Co., 1963. Russell EJ, George AE, Kricheff I1, Budzilovich G. Atypical computed tomographic features of intracranial meningioma. Radiology 1980;135:673-82. Stefan H. Lipom lokalisiert im Kleinhirnbruckenwinkel als Nebenbefund einer tuberculosen Meningitis mit histologischem Befund. Z Gesamte Neurol Psychiatr 1933;145:445-53. Vonderahe AR, Niemer WT. Intracranial lipoma. A report of four cases. J Neuropathol Exp Neurol 1944;3:344-54. Winther LK, Reske-Nielsen E. Intracranial lipoma. Report of a case and differentiation from other tumors of cerebellopontine angle. J Laryngol Otol 1978;92:351-6. Zimmerman RA, Bilaniuk LT, Dolinskas C, Cranial computed tomography of epidermoid and congenital fatty tumors of maldevelopmental origin. Comput Tomogr 1979;3:40-50.
Surg Neurol 1985;23:134-8
Cerebellopontine Angle Lipoma Shelley B. Rosenbloom, M.D., Benjamin S. Carson, M.D., Henry Wang, M.D., Arthur E. Rosenbaum, M.D., and George B. Udvarhelyi, M.D. Departments of Neuroradiology and Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
Lipomas rarely occur intracranially. Moreover, the cerebellopontine angle is one of the more unusual sites of such hamartomas. Of the 11 reported cases, all but three caused symptoms related to compression of the cranial nerves in the cerebellopontine angle. Only three separate cases have been studied by computed tomography, and in one the fat density was not recognized. This report deals with the clinical presentations, surgical management, and radiologic assessment of these lesions.
1) matching the density o f the orbital fat. N o enhancement was detected. The fourth ventricle was in the midline; the lack of mass effect on the ventricle suggested a soft tumor. The internal auditory canals were symmetric and there was no erosion of bone (Figure 2). Coronal and sagittal computer reconstructions demonstrated that the lesion was confined to the infratentorial compartment and abutted the posterior wall of the petrous ridge (Figures 3 and 4). Left vertebral angiography was unremarkable except for possible medial displacement of the left anterior inferior cerebellar artery.
KEY WORDS: Cerebellopontine angle tumor; Lipoma; Computed tomography; Differential diagnosis; Radiologic assessment; Surgical management
Surgery
Rosenbloom SB, Carson BS, Wang H, Rosenbaum AE, Udvarhelyi GB. Cerebellopontine angle lipoma. Surg Neurol 1985;23:134-8.
Clinical Presentation A 28-year-old man presented with chronic left-sided dull and persistent supraorbital and maxillary headaches. H e had had episodes of nausea and dizziness for 1 year. T h e r e was no history of hearing loss. Physical examination disclosed minimal left ptosis and sensory impairment in the ophthalmic and mandibular distribution of the fifth cranial nerve on the left side of the face. The left pupil was slightly smaller than the right, but both reacted normally to light and on accommodation. The neurological examination was otherwise unremarkable, including auditory and cerebellar functions. Laboratory auditory and vestibular testing showed a partial paralysis of the left semicircular canal vestibular reflex. Radiologic Assessment Computed tomography (CT) scans performed before and after intravenous enhancement demonstrated a hypodense lesion in the left cerebellopontine angle (Figure
Utilizing the park bench position, a left paramastoidsuboccipital craniectomy was performed. A yellow mass the size o f a large walnut was immediately identified in the cerebellopontine angle as the left cerebellar hemisphere was retracted medially. The tumor incorporated portions of seventh, eighth, and ninth cranial nerves and was juxtaposed to the postero-superior aspect of the trigeminal nerve (first and second divisions) producing some displacement of these structures (Figure 5). The tumor was surgically separated from the fifth nerve and debulked, but intrinsic fibrous septa, abundant blood vessels, and adherence to the cranial nerves and brainstem precluded total resection. During the surgical manipulation, the eighth nerve, which merged with the lesion, became more attenuated. A pathological report of fibroadipose tissue consistent with lipoma was returned. The patient did well postoperatively with complete alleviation of head and facial pain. Subsequently, he experienced a significant decline in left auditory function and eventually developed some recurrent dizziness.
Discussion
Incidence Address reprint requests to: George B. Udvarhelyi, M.D., Johns
Hopkins Medical Institutions, Hampton House 255, 624 N. Broadway, Baltimore, Maryland 21205. © 1985 by ElsevierSciencePublishing Co., Inc.
Intracranial lipomas are rare lesions in both autopsy and CT experience. Vonderahe et al [ 13] reported 4 among 0090-3019/85/$3.30
Cerebellopontine Angle Lipoma
Surg Neurol 1985;23:134-8
135
Figure 3. Sagittally reconstructed image at the level of the anterior clinoid demonstrates the opposition of the lipoma to the posterior aspect of the petrous ridge.
Figure 1. Reversed axial C T image at the level of the internal auditory canals demonstrates a fat-density lesion lying in the cerebellopontine angle cistern. The lesion has remarkably little mass effect for its size: there is no apparent displacement of the tonsils or vallecula. 5000 autopsies. In neuropathological autopsy series, their influence is higher (9 in 1956 tumor cases from 4290 neurosurgical autopsies) [1]. Kazner et al [5] reported only 11 from 17,500 CT examinations. Zimmerman et Figure 2. Wide-windowed C T image demonstrates no evidence of bone erosion of internal auditory canal asymmetry.
al [15] found 10 cases among 700 intracranial tumors diagnosed by CT scans (1.3%). Most intracranial lipomas occur in the pericallosal cistern and may be associated with other cerebral malformations, particularly hypoplasia of the corpus callosum [10]. Krainer's series [7] lists the following additional characteristic locations for lipoma: ambient and quadrigeminal cisterns, interpeduncular fossa cisterns, suprasellar and perihypophyseal cisterns, olfactory cistern, sylvian cistern, cerebellopontine angle cistern, cisterna magna, tela choroidea of the lateral and third ventricles, their choroid plexus, and associated cisternal vela. Whereas lipoma of the pericallosal cistern is frequently associated with neurological abnormalities (especially convulsive seizures), these may be attributed to associated dysgenetic abnormalities (heterotopias, microcephaly, polymicrogyria, etc.). Pericallosal cistern lipomas have been discovered in neurologically normal people (e.g., Budkha [1] case 11). Nonetheless, with the ex-
Figure 4. Coronal computed reconstruction demonstrates that the lesion is entirely infratentorial and immediate(~ adjacent to the medial aspect of the petrous ridge. ~..... ~ii¸
. ~i~i ~ i!~ ¸¸~¸
7ii!¸~¸¸
~
~!
136
Surg Neurol 1985 ;23:134-8
Rosenbloom et al
Figure 5. Intraoperative photograph. T = tumor; C = cerebellum; arrow =attenuated 7th and 8th nerves; asterisk = lower cranial nerves; note branches of antero-inferior cerebellar artery above the tumor and impingement of the superior-medial portion of the tumor on the 5 th cranial nerve.
ception of pericallosal cistern lipoma, intracranial lipomas are usually incidental findings and are not associated with neurological symptoms unless they produce hydrocephalus. Cerebellopontine angle lesions have a higher incidence o f focal neurologic findings (especially eighth nerve dysfunction) than other intracranial lipomas (except pericallosal cistern lipomas). At least 9 of 12 were symptomatic (Table 1). These lesions occur predominantly on the left (10 of 12 cases) and in males (9 of 12 cases). T h e age o f presentation also varies widely, 17 months [2] to 77 years [ 1], with no distinguishable peak.
Radiologic
Differential
Diagnosis
Prior to CT scanning, no useful method for differentiating lipoma preoperatively from other cerebellopontine angle masses was available. Radiographic studies have sh~own enlargement o f the internal auditory canal, characteristic o f acoustic neuromas, in four lipomas [3,9,14]. Symmetric internal auditory canals are reported in one previous case [8]. Cisternography (iodinated contrast or gas) is reported in five cases. Nonfilling o f the internal auditory canal, cisternal mass, or cisternal obliteration (Fukui) was shown in all o f these [3,8,9,14], although the mass was not detected on an
initial study in one case [9]. Vertebral angiography has been reported as unremarkable or showing only mass effect in two cases [4,8]. In one patient, a dilated, tortuous distal anterior-inferior cerebellar artery, ipsilateral to the lesion, was described [3]. Computed tomography studies of cerebellopontine angle lipomas have been reported in this and in three previous cases [2,4,8]. In the single negative CT study [8], an ~ 11-mm tumor was discovered surgically. The type of CT scanner and quality of the CT examination are not described. Lipomas o f the cerebellopontine angle have been identified on CT previously in two cases. Faerber and Wolpert [2] demonstrated a very large, fatdensity tumor extending into the middle fossa from the cerebellopontine angle. N o surgical confirmation is available in this case. Graves and Schemm [4] demonstrated a 1.5-cm tumor measuring - 2 5 to - 4 5 Hounsfield units which was operated upon and confirmed. The present case appears to be the first examined with a highresolution x-ray CT unit (Siemens DR3). Although the CT appearance of the cerebellopontine angle lipoma is characteristic, there are differential considerations. Low-density lesions of the cerebellopontine angle include: cystic acoustic neuromas, cystic or fatty meningiomas, epidermoids, arachnoid cysts, cystic or necrotic metastases, and dermoids (see Table 2). Nonlipomatous fatty tumors such as hibernomas do not seem to appear in the cerebellopontine angle. Acoustic neuroma, by far the commonest cerebellopontine angle tumor, characteristically demonstrates CT numbers higher than those of fat and usually brighter on intravenous enhancement. Most cause widening of the internal auditory canal. Meningiomas, the second most common masses in the cerebellopontine angle, are usually hypodense lesions. When necrotic or cystic, they may appear hypodense, but usually heterogeneously so, and are associated with at least minimal intravenous enhancement. The CT numbers are characteristically higher than those of fat. Lipomatous infiltration was demonstrated histologically in 5% or 6 of 131 consecutive meningiomas reviewed by Russell et al [11]. The CT appearance of these tumors was atypical in four cases, but none was sufficiently hypodense to suggest a fatty component on CT. The third most common cerebellopontine angle tumor, epidermoid, may also present as a low-density lesion on CT. In the report by Zimmerman et al [15], of 27 intracranial tumors o f maldevelopmental origin (12 lipomas, 10 epidermoids, 4 dermoids, and 1 teratoma), intracranial fat was detectable by low CT number in lipomas, dermoids, and the teratoma, but not in their cases of epidermoid. Only 3 of 35 dermoids were described as partially fatty in combining several series. Epidermoids were of cerebrospinal fluid equivalent den-
C e r e b e l l o p o n t i n e A n g l e Lipoma
T a b l e 1.
Surg N e u r o l 1985;23:134-8
137
Clinical Features of CerebellopontineAngle Lipoma
Source
Age/sex
l. Klob [6] (1859)
Autopsy or surgical
M
2. Stefan [12] (1933)
40/F
A
3. Budka [1] (1974)
77/M
A
4. Budka [1] (1974)
26/F
5. Faerber [2] (1976)
17 mos/M
Symptoms
Radiographic findings
Bright's disease 8th nerve dysfunction TB meningitis No pertinent clinical symptoms Head trauma
Pathology Fatty tumor Olive-sized lesion Fat cells infiltrating meninges Calcification in adjacent brain Hypertrophy of nerves within the tumor Plaque of mixed tissue in pontine gray matter Lipomatous infiltration of 8th
5th and 8th nerve dysfunction
nerv~2
CT: Fatty tumor extending from CPA to suprasellar cistern Skull x-ray: bone erosion Vertebral angio: dilated AICA PEG: L CPA tumor PEG: L CPA tumor
Not described
6. Fukui [3] (1977)
28/F
S
8th nerve dysfunction
7. Winther [ 14] (1978)
50/M
S
8th nerve dysfunction
8. Olson [9] (1978)
42/M
S
TB meningitis 8th nerve dysfunction
Polytome: bone erosion Posterior fossa myelogram
None
Thinly encapsulated tumor attached to arachnoid of left cerebellar hemisphere and brainstem Fatty tumor infiltrating 7th to 10th cranial nerves with a thin capsule laterally but not medially. Adherent brainstem Unencapsulated 7.5-mm tumor
Abbreviations: CPA - cerebellopontine angle; PEG - pneumoencephalogram; L - left; AICA = antero-inferior cerebellar artery.
sity i n 9 o f 2 0 l e s i o n s [ 1 5 ] a n d i n 17 o f 2 5 c a s e s i n t h e literature. Two were partially calcified; their hypodensity w a s a t t r i b u t e d t o a d m i x t u r e o f h y p e r d e n s e k e r a t i n -
T a b l e 2.
ized, proteinaceous debris and hypodense cholesterin (with or without calcification) due to saponification. A r a c h n o i d cysts a r e usually c o n s i d e r e d t h e f o u r t h m o s t
Computed Tomography of Hypodense CerebellopontineAngle Lesions."Differential Diagnosis C T Density
Fat Content
Calcium
Enhancement
Effect on Bone
Acoustic schwannoma Meningioma
Heterogeneous; usually isodense Usually hyperdense
None
Uncommon
Usually present
Rare
Frequent
Usually present
Epidermoid
Usually CSF density; may be heterogeneous; thin wall usually Usually CSF density; thin wall Usually mixed density; thick wall usually
Seen in 3 of 35 cases on CT None
Seen in 2 of 35 cases
Not present
Erodes IAC; may erode petrous ridge May produce hyperostosis; erosion unusual May erode bone
None
Not present
May erode bone
Not present
May be associated with transcalvarial sinus tract
Cystic or necrotic lesions usually have thick, nodular walls Fatty; uniform
None
In 6 of 9 cases reported may be dental elements Rare
Present
May erode bone
Present
Not reported
None
May erode bone (4 of 6 cases)
Arachnoid cyst Dermoid
Metastasis
Lipoma
Partially fatty in 3 of 4 cases
Abbreviations: CT = computed tomography; 1AC = internal auditory canal.
138
Surg N e u r o l 1985;23:134-8
common cerebellopontine angle tumor. Characteristically of cerebrospinal fluid density, they may occasionally be slightly denser and may remodel the adjacent bone. Fatty components or calcification are not concomitants. Dermoid tumors are rare in the cerebellopontine angle and tend to occur in the midline. Calcification on CT scanning was noted in six of nine cases [15] and ectodermal and mesodermal elements (hair, sebaceous glands, apocrine glands) contributed to the focal hypodensity of"fat" on CT [15]. The heterogeneous density of these lesions and their rarity beyond the midline aid the diagnostician. Summary Cerebellopontine angle lipomas are rare. Characteristics for consideration in the differential diagnosis of hypodense lesions on x-ray CT scanning were discussed. The clinical presentation of these lesions is characteristic of a cerebellopontine angle mass. Their excision is difficult because of adherence to cranial nerves and the brainstem and infiltration of blood vessels. The surgical objectives are often limited to decompression even using the operating microscope.
R o s e n b l o o m et al
3. 4.
5.
6. 7. 8.
9. 10. 11.
12.
13. 14.
References 1. Budka H. Intracranial lipomatous hamartomas (intracranial "lipomas"). Acta Neuropathol (Berl) 1974;28:205-22. 2. Faerber EN, Wolpert SM. The value of computed tomography
15.
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