Inner Ear Signal Abnormalities of Adjacent Intracranial Lipochoristoma
======================================================================

* John C. Benson
* Matthew L. Carlson
* Karl R. Khandalavala
* Girish Bathla
* Paul J. Farnsworth
* Jamie J. Van Gompel
* John T. Wald
* John I. Lane

## Graphical Abstract

![Figure1](http://www.ajnr.org/https://ajnr-sso.highwirestaging.com/content/ajnr/early/2025/04/10/ajnr.A8603/F1.medium.gif)

[Figure1](http://www.ajnr.org/content/early/2025/04/10/ajnr.A8603/F1)

## Abstract

**BACKGROUND AND PURPOSE:** Inner ear signal abnormalities commonly develop in cases of vestibular schwannoma and are associated with hearing loss. Whether such signal alterations occur in other masses of the internal auditory canal (IAC), however, remains unknown. Here, we assessed inner ear signal abnormalities of lipochoristomas, historically termed “lipomas,” involving the IAC and cerebellopontine angle (CPA).

**MATERIALS AND METHODS:** A retrospective review was completed of patients with an MRI of an IAC and/or CPA intracranial lipochoristoma. The signal intensity of the ipsilateral labyrinthine structures was both subjectively and objectively compared with the contralateral side on FLAIR, FSE, T2 sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE sequence) and gradient recalled-echo (CISS) images by 2 neuroradiologists. Any initial disagreements were resolved by joint review to establish a consensus.

**RESULTS:** Fourteen patients were included. The average age was 53.1 (SD, 11.7) years, and 6 patients (42.9%) were women. Twelve of 14 (86%) of the lipochoristomas were in the IAC; the remaining masses were in the CPA. Regarding subjective assessment of abnormal labyrinthine signal, there was perfect interobserver agreement using FLAIR and T2 SPACE images; the Fleiss κ for CISS images was 0.7379. After consensus review, abnormal signal was noted in the adjacent labyrinthine structures in most cases on FLAIR (75%) and T2 CISS (73%); only 8% of patients had abnormal signal on T2 SPACE. Objective measurements of the cochlear signal similarly demonstrated relatively increased ipsilateral signal on FLAIR (*P* = .011) and relatively decreased signal on T2 CISS (*P* = .046). No significant difference was noted between ipsilateral and contralateral measurements on T2 SPACE (*P* = .093).

**CONCLUSIONS:** Abnormally increased FLAIR signal and decreased T2 CISS signal are present in most ipsilateral labyrinthine structures in patients with IAC and/or CPA lipochoristomas. Thus, these labyrinthine signal alterations are not exclusively restricted to vestibular schwannomas.

## ABBREVIATIONS:

CPA
:   cerebellopontine angle
IAC
:   internal auditory canal
PTA
:   pure tone average
VS
:   vestibular schwannoma
WRS
:   word recognition score

SUMMARY

#### PREVIOUS LITERATURE:

This is the first study to specifically assess inner ear signal alterations of adjacent lipochoristomas. Prior studies have focused on other tumors, particularly vestibular schwannomas.

#### KEY FINDINGS:

Inner ear signal abnormalities are present on multiple MRI sequences of ipsilateral IAC and/or CPA lipochoristomas.

#### KNOWLEDGE ADVANCEMENT:

Labyrinthine signal alterations are not exclusively seen with vestibular schwannomas, possibly changing our understanding of the biomechanism of such findings.

Intracranial lipochoristomas, historically termed “lipomas,” are considered congenital malformations, arising from aberrant differentiation of the meninx primitiva. Growth of these lesions may coincide with somatic growth, for example during puberty; however, growth of lesions during adulthood is exceptional.1,–,3 Furthermore, they characteristically engulf or surround coursing nerves and vessels, as opposed to benign tumors that typically push adjacent anatomy along the tumor capsule edge. Approximately 10% of intracranial lipochoristomas occur in the internal auditory canal (IAC).4 Symptoms associated with lipochoristomas in the IAC and/or cerebellopontine angle (CPA) are uncommon. Despite a propensity for nongrowth, lesions in these locations paradoxically present with progressive sensorineural hearing loss, rotatory vertigo, tinnitus, and, less commonly, other forms of cranial neuropathy.5 The imaging appearance of intracranial lipochoristoma is pathognomonic: The masses appear as fat-density masses on CT and have signal intensities that mimic macroscopic fat on all MRI sequences including subtracting with fat-suppression technique.6,7 

Recently, there has been growing interest in the assessment of labyrinthine structures of the IAC and/or CPA masses. Abnormalities of inner ear structures have long been specifically studied in vestibular schwannomas (VSs), the most common type of CPA tumor.8 VSs are commonly associated with signal alterations in the ipsilateral labyrinthine structures, which classically demonstrate decreased signal intensity on high-resolution T2 images and increased signal on postcontrast T2 FLAIR images.9,10 A recent study also found signal alterations in the ipsilateral perilymphatic fluid in the setting of adjacent meningiomas.11 These signal alterations are of clinical importance because they are associated with the degree of ipsilateral hearing loss.12,13 The pathophysiology of these changes remains incompletely understood and may include increases in proteins and metabolites, elevated blood-labyrinthine barrier permeability, and/or tumor “shedding.”13,14

To date, however, our knowledge of inner ear signal changes of adjacent masses remains essentially restricted to VSs. It remains unknown whether the phenomenon of inner ear signal alterations also occurs with other masses such as lipochoristomas and meningiomas. The presence or absence of inner ear abnormalities related to other masses would further our understanding of the underlying biomechanism by which signal alterations arise. Thus, this study set out to assess whether abnormal signal intensities are observed in the ipsilateral inner ear structures of patients with IAC and/or CPA lipochoristomas.

## MATERIALS AND METHODS

### Patient Selection

This study was performed following approval by the local institutional review board. A retrospective review was completed of suspected intracranial lipochoristomas located in the IAC or CPA between 2007 and 2023. Included patients had dedicated IAC MRI available for review. The diagnosis of lipochoristoma was based on the imaging appearance on MRI, with intralesional signal intensity matching macroscopic fat on all sequences, including fat-saturated sequences. Patients were excluded if the diagnosis of lipochoristoma could not be confidently established during the final review (*n* = 2) or if imaging was substantially degraded by artifacts (eg, motion) (*n* = 0). In addition, 1 patient was excluded for having both a CPA lipochoristoma and a presumed intralabyrinthine schwannoma. Demographic information and clinical history were assessed using a retrospective review of the electronic medical record.

### MRI Parameters

All examinations were performed on a 3T scanner with multichannel phased array coils (either a 32- or a 64-channel head coil). The dedicated IAC sequences reviewed included an axial 3D T2 sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE; Siemens) sequence (TR = 1300 ms, TE = 184 ms, data matrix = 320 × 320, acquisition time = 3:55 minutes) and/or axial CISS (TR = 4700 ms, TE = 200 ms, data matrix = 192 × 192, acquisition time = 4:46 minutes) and an axial 3D postcontrast FLAIR (TR =5 000 ms, TE = 379 ms, data matrix = 192 × 192, acquisition time = 4:29 minutes). The field of view for every sequence was 150 mm.

### Imaging Review

Independent retrospective reviews were performed by 2 Certificate of Added Qualification–certified neuroradiologists with >20 and >5 years’ experience in temporal bone research and interpretation (J.I.L. and J.C.B., respectively). Reviewers were blinded to the audiogram results. All lipochoristomas were evaluated on the basis of location (IAC, CPA), laterality, and size. Size was recorded as the largest diameter in any measured axis. It was also noted whether lesions partly or completely occluded the IAC.

Inner ear signal alterations were assessed on high-resolution T2 SPACE and/or CISS and FLAIR images. Because these examinations were performed during multiple years, there was some variability in terms of whether high-resolution T2-weighted images were performed using FSE (eg, T2 SPACE) or GRE (eg, T2 CISS) images. For T2 SPACE/CISS and FLAIR sequences, the reviewers subjectively compared the signal intensity of the inner ears ipsilateral to the lipochoristoma with the contralateral side. The inner ear signal was considered abnormal if it was relatively decreased compared with the contralateral side on T2 SPACE or T2 CISS images, or relatively increased on FLAIR images. Any interobserver disagreements regarding the presence or absence of inner ear signal abnormalities were resolved by consensus.

In addition, the signal intensity of the ipsilateral and contralateral cochlea was objectively measured by a signal Certificate of Added Qualification–certified neuroradiologist (J.C.B.) on T2 (SPACE and/or CISS) and FLAIR images, using the average measured signal intensity within the ROI (Fig 1). To obtain these ROI measurements, we assessed images either in a direct axial plane or in a slightly reformatted near-axial plane to optimize visualization of the cochlea. The ROI was placed near the apex of the cochlea to maximally measure of the inner ear fluid while minimizing the measurement of the modiolus and adjacent osseous structures. Each ROI circle was manually created to match the cochlear size; a standardized ROI circle size was used.

![FIG 1.](http://www.ajnr.org/https://ajnr-sso.highwirestaging.com/content/ajnr/early/2025/04/10/ajnr.A8603/F2.medium.gif)

[FIG 1.](http://www.ajnr.org/content/early/2025/04/10/ajnr.A8603/F2)

FIG 1. 
Methodology for measuring signal intensity of the ipsilateral cochlea, shown here on axial 3D T2 SPACE (*A*) and postcontrast FLAIR (*B*) images. A lipochoristoma is seen in the left IAC. Circumf indicates circumference; min, minimum; max, maximum, dia, diameter. 

### Audiometric Data

To assess the association with hearing, we compared subjective and objective measures of signal alterations with the closest available audiogram corresponding to the MRI study. Both pure tone average (PTA) and word recognition score (WRS) were collected and evaluated. Associations with imaging findings and hearing loss were explored, including the 4-frequency PTA (0.5, 1, 2, 3 kHz) and WRS.

### Statistical Analyses

Means (SDs) of observed abnormalities were calculated for all categoric variables. The frequency of observed abnormalities was calculated for all categoric variables. Statistical calculations were performed using BlueSky Statistics software (Bluesky Statistics). A paired Student *t* test was used to compare continuous variables. The Fleiss κ was used to calculate interobserver agreement with categoric variables. The threshold for statistical significance was set to *P* < .05.

## RESULTS

Fourteen patients met the inclusion criteria and were included in the final cohort of this study (Table 1). The average age was 53.1 (SD, 11.7) years; 6 patients (42.9%) were women. Most (8/14; 64.3%) intracranial lipochoristomas were located on the left side. Twelve of 14 (85.7%) lipochoristomas were located in the IAC, while the remaining 2 (14.3%) were located in the CPA. All but 1 lesion partly or completely occluded the IAC. The average size, based on maximum measured diameter, was 7.4 (SD, 6.1) mm. All except 1 patient (92.9%) had T2 SPACE imaging available for review. Twelve of 14 (85.7%) included patients had IAC FLAIR images (with 7/12 postcontrast FLAIR and the rest noncontrast FLAIR), and 11/14 (78.6%) had CISS images for review.

View this table:
[Table 1:](http://www.ajnr.org/content/early/2025/04/10/ajnr.A8603/T1)

Table 1: 
Demographics of the included cohort

Of the inner ear structures assessed on IAC FLAIR, 3D T2 SPACE, and T2 CISS, a total of 3 interobserver disagreements occurred. All 3 disagreements were on 3D T2 GRE images, with the Fleiss κ calculated at 0.7379. Perfect interobserver agreement was noted on FLAIR and T2 SPACE interpretations.

After consensus review, ipsilateral labyrinthine signal alterations were most commonly observed on IAC FLAIR images, with 9/12 (75.0%) patients noted to have increased signal in the adjacent inner ear structures. Eight of 11 (72.7%) had relatively decreased labyrinthine signal on 3D T2 CISS images. Only 1 patient (1/13; 7.7%) had decreased/abnormal signal in the ipsilateral inner ear on 3D T2 SPACE images (Fig 2). No subjective inner ear signal alterations were seen in the patients in whom the lesion did not obstruct the IAC, though only CISS sequences were available for review.

![FIG 2.](http://www.ajnr.org/https://ajnr-sso.highwirestaging.com/content/ajnr/early/2025/04/10/ajnr.A8603/F3.medium.gif)

[FIG 2.](http://www.ajnr.org/content/early/2025/04/10/ajnr.A8603/F3)

FIG 2. 
Evaluation of the inner ear structures on axial T2 SPACE (*A* and *B*) and postcontrast 3D FLAIR (*C* and *D*). A lipochoristoma is noted in the left IAC (*arrows*). The inner ear signal intensity subjectively increases on 3D FLAIR images (*dashed ovals*).

Objective measurements of the labyrinthine structures showed that FLAIR signal was, on average, greater in the ipsilateral cochlea than on the contralateral side (64.8 [SD, 32.8] and 48.8 [SD, 21.1], respectively; *P* = .011). Signal on 3D GRE images was decreased in the ipsilateral cochlea compared with the contralateral side (3548.6 [SD, 3351.8] and 4112.7 [SD, 3806.3], respectively; *P* = .046). On T2 SPACE images, the ipsilateral and contralateral cochlea measured 480.4 (SD, 133.3) and 514.8 (SD, 128.8), respectively. This difference approached, but did not reach, statistical significance (*P* = .093).

The average time between MRI and the audiogram was 387 (SD, 1052) days (median, 9 days). The larger lesion side was associated with PTA dB values of 0 = 0.0016 and decreased WRS percentages (*P* < .001). If one allowed for the single patient with subjectively abnormal values noted on T2 SPACE images, the average ipsilateral PTA was higher in the patient with subjectively abnormal ipsilateral labyrinthine signal (72.0) than in those with a subjectively normal ipsilateral signal (31.6) (*P* = .027). There were no significant differences noted between subjective ipsilateral inner ear signal and audiogram results (Table 2). Objectively, no statistically significant associations were noted between the inner ear signal (calculated as a ratio between ipsilateral and contralateral structures) and the PTA/WRS audiogram results (*P* values ranged between .19 and .76).

View this table:
[Table 2:](http://www.ajnr.org/content/early/2025/04/10/ajnr.A8603/T2)

Table 2: 
Associations between subjective ipsilateral inner ear abnormalities and audiogram testing PTA and WRS

## DISCUSSION

This study sought to assess whether inner ear signal alterations are present in patients with intracranial lipochoristoma located in the IAC or CPA. The results indicate that such abnormalities are observed in most patients on both IAC FLAIR images and T2 CISS images. Specifically, the signal in the inner ears ipsilateral to the lipochoristoma is relatively hypointense to the contralateral structures on T2 CISS and relatively hyperintense to the contralateral side on FLAIR. On T2 SPACE images, subjective differences are rarely noted, though the objectively measured signal intensities did approach a statistically significant difference. Overall, there was little relationship noted between the signal alterations and audiograms; subjectively abnormal signal in the ipsilateral inner ear on T2 SPACE was associated with poorer PTA results, though this result must be interpreted in the context of only a single patient with subjectively abnormal T2 SPACE signal.

The most immediate impact of this study is that it shows, for the first time, that inner ear signal alterations of intracranial masses are not restricted to VSs and meningiomas. As noted above, VSs have long been known to be associated with abnormal-appearing ipsilateral labyrinthine structures, with signal that is similarly hyperintense on FLAIR and hypointense on high-resolution T2-weighted images.15 More recently, in fact, our understanding of inner ear changes of an ipsilateral VS has become more nuanced. It is now known, for example, that more abnormal signal intensities in the inner ear are associated with larger and more solid VSs.16 VSs causing mass effect on the adjacent brainstem also have more abnormal inner ear signal alterations, possibly owing to greater tumoral size.17

Symptomatic CPA and/or IAC lipochoristomas have been reported, though descriptions of labyrinthine signal alterations in the setting of these masses are sparse. Filli et al,18 for example, described an IAC lipochoristoma associated with ipsilateral hearing loss but did not describe any corresponding abnormalities in the adjacent inner ear. Thus, it remains unknown whether symptoms related to these lipochoristomas are due to mass effect or the observed inner ear abnormalities.

Most interesting, 1 hypothesis within the VS literature is that inner ear signal changes reflect protein products that are shed by the tumor and accumulate in the fundus and labyrinth. One aspect of lipochoristomas that is particularly relevant is that they are a congenital malformation and generally do not grow and therefore presumably might behave differently than a VS. Although further investigation is required, the findings in this study might suggest that the tumors are not implicated in “toxic protein shedding” but merely block perilymph/CSF circulation of the inner ear and fundus. If this suggestion is indeed true, we would expect to see similar findings with other lesions that may “block” the IAC or porus acusticus, such as meningiomas or osteomas. It would also not fully explain the idea that nonoccluding lesions (ie, those that are smaller than the cross-section diameter of the IAC) are also commonly associated with progressive hearing loss).

Overall, the results seem to indicate that the observed signal alterations have little, if any, effect on hearing function. Nevertheless, it remains to be seen whether the signal abnormalities observed in the ipsilateral labyrinthine structures have prognostic value, particularly in terms of future hearing loss. Again, our knowledge of this subject remains essentially restricted to patients with VSs. For example, is it known that labyrinthine enhancement can precede cochlear obliteration after VS resection.19 Wagner et al20 found an association between inner ear signal intensity on T2 CISS sequences and vertigo symptoms. Signal alterations are also associated with hearing function. Yamazaki et al,21 for example, found that postcontrast 3D FLAIR signal intensity in the ipsilateral inner ear structures was associated with hearing level. Jones et al22 similarly found that abnormal cochlear T2 CISS signal is associated with greater degrees of hearing loss in conservatively managed patients with VSs. These signal alterations may resolve following successful hearing-preservation surgeries.23 However, the expected evolution of signal alterations after surgery may depend on the surgical approach used.24

This study has several limitations. Its small patient cohort did not allow statistical control for potential founders. The time interval between MRI and audiometric data acquisition was also variable and skewed. Also, different types of MRI sequences were used; T2 SPACE and/or CISS were obtained variably, sometimes in different examinations. In addition, the potential for selection bias in this cohort may exclude relevant patient populations and thus limits the generalizability of the findings. Next, because these patients were scanned during a wide time span, changes in MRI technology and techniques may have affected differences in subjective findings and measured signal intensities. Also, the relatively long average time difference between the audiograms and MRIs could impact the interpretation of the results. Next, there was heterogeneity of the FLAIR images, with some obtained without and others with contrast. In addition, data regarding the current and/or future hearing disabilities of the included patients were not obtained as part of this study. Consequently, as stated above, our capability of assessing the clinical impact of the observed signal alterations remains limited at this time. Finally, although the masses represented presumed intracranial lipochoristomas based on their imaging characteristics, no histologic tissue was available for review; thus, they did not represent pathologically proved lipochoristomas.

## CONCLUSIONS

Abnormal signal, increased on FLAIR and decreased on T2 CISS, is present in most ipsilateral labyrinthine structures in patients with intracranial lipochoristomas located in the IAC or CPA. The ipsilateral inner ear signal on T2 SPACE, conversely, is nearly always subjectively normal and not statistically different on objective measurements. These results indicate that labyrinthine signal alterations in the setting of intracranial masses are not exclusively seen with VSs. Further research may be useful to decipher whether these observations correspond to hearing ability and/or portend future hearing loss. Additionally, these data may implicate IAC blockage with labyrinthine metabolite buildup as a cause of sensorineural hearing loss, rather than tumor protein shedding.

## Footnotes

*   [Disclosure forms](https://www.ajnr.org/sites/default/files/additional-assets/Disclosures/May%202025/0914.pdf) provided by the authors are available with the full text and PDF of this article at [www.ajnr.org](http://www.ajnr.org).

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*   Received September 13, 2024.
*   Accepted after revision October 16, 2024.


*   © 2025 by American Journal of Neuroradiology