A Rare Case of Coexisting Middle Ear Salivary Gland Choristoma and Lipoma

Abstract

Middle ear salivary gland choristoma (SGCh) is an exceptionally rare benign tumor characterized by middle ear malformations accompanied by unilateral conductive hearing loss. Early diagnosis remains particularly challenging, and surgical excision constitutes the primary therapeutic approach. We present a 13-year-old male with congenital hearing impairment diagnosed with SGCh and surgically managed. This report describes the first documented case of SGCh coexisting with middle ear lipoma, analyzing its clinical presentation, imaging differential diagnostic challenges, and surgical management strategy to advance precise diagnostic and therapeutic interventions.

Introduction

Middle ear salivary gland choristoma (SGCh) refers to ectopic salivary gland tissue within the middle ear cavity, commonly involving the ossicular chain with potential facial nerve proximity. Most patients present with conductive hearing loss despite intact tympanic membranes. To our knowledge, Taylor and Martin first described this entity in 1961, ¹ with only approximately 50 cases reported to date. We report a rare case of SGCh coexisting with middle ear lipoma, successfully treated via complete surgical resection with favorable postoperative outcomes. This study reviews existing literature on both pathologies and explores their clinical and embryological correlations.

Case Report

A 13-year-old male patient was diagnosed with left-sided congenital hearing loss at birth during neonatal hearing screening. The exact screening date was not recorded, and no further evaluation or treatment was performed for more than 10 years. He presented to our hospital on June 24, 2023, due to persistent hearing loss affecting daily life and study. The patient was of Han Chinese ethnicity. There was no family history of congenital hearing loss, middle ear malformation, or genetic syndromes. His general growth and development were normal for his age, with no evidence of developmental delay or other congenital anomalies. No subsequent intervention was pursued during the course of the disease, and the hearing deficit remained stable without progression, otalgia, otorrhea, or tinnitus.

Physical examination showed intact bilateral tympanic membranes. Tuning fork tests indicated left-sided conductive hearing loss (Weber test left-deviated, Rinne test negative, Schwabach test positive, Gelle test positive). Pure-tone audiometry revealed a 60 dB air-bone gap in the left ear, with normal hearing in the right ear. Tympanometry showed Type As curves bilaterally. High-resolution temporal bone CT revealed a soft-tissue density mass in the left mesotympanum attached to the incus long process, with an unclear stapes structure. Based on the congenital presentation, conductive hearing loss, and CT findings, a provisional diagnosis of congenital middle ear cholesteatoma was established.

Following the provisional diagnosis of middle ear cholesteatoma and exclusion of surgical contraindications, the patient underwent endoscopic transcanal tympanotomy under general anesthesia on July 27, 2023. A postauricular incision was made to elevate the tympanomeatal flap, followed by dissection of the fibrous annulus and anterior reflection of the tympanic membrane to access the mesotympanum. Intraoperative exploration revealed a smooth-surfaced, yellowish-white mass localized in the posterosuperior tympanic cavity, with the facial nerve coursing inferolaterally to the lesion. Subsequent atticotomy demonstrated extension of the mass to the posterior segment of the horizontal facial nerve, displaying granular surface projections. The lesion enveloped the stapes superstructure, which exhibited preserved mobility despite stapedial deformity, while incudal hypoplasia was observed with intact malleus mobility. The encapsulated mass, containing amorphous yellowish material with crystalline inclusions, was meticulously excised in toto with careful preservation of the facial nerve. Partial removal of the overhanging facial canal bone facilitated exposure of the stapes footplate. Ossiculoplasty was then performed using autologous tragal cartilage to reconstruct the ossicular chain, followed by anatomical repositioning of the tympanic membrane to restore middle ear integrity (Figures 1 and 2).

Figure 1.

Axial CT showing soft tissue density in left tympanic cavity

Figure 2.

Histopathology: 2a: Mature adipocytes confirming lipoma;2b:Salivary acini with pseudostratified ciliated epithelium (H&E, ×100)

The patient experienced an uncomplicated postoperative recovery. Following systematic postoperative assessment, the patient showed no wound erythema or infection, no otorrhea, an intact tympanic membrane without perforation, and no intracranial or extracranial complications such as gustatory disturbance, facial nerve paralysis, or vertigo. Significant subjective hearing improvement was reported on postoperative day 1. Pure-tone audiometry at 2 weeks postoperatively demonstrated a left ear air conduction threshold averaging 40 dB, with an air-bone gap of approximately 20 dB, reflecting marked improvement compared to preoperative baselines. At the 1-year follow-up, audiometric evaluation revealed sustained progress: the left ear air conduction threshold stabilized at 38 dB, with a persistent air-bone gap of 28 dB. This slight widening of the air-bone gap was attributable to a mild elevation in bone conduction threshold, while air conduction remained stable. These findings effectively rule out ossicular prosthesis migration, and the change most likely reflects subtle cartilage resorption and audiometric variability. Serial otoscopic and radiological assessments confirmed no evidence of recurrent middle ear pathology. Although persistent hearing loss remained in the left ear, the overall auditory function exhibited substantial recovery relative to preoperative status.

Histopathological examination of the excised specimen identified normal salivary gland tissue admixed with mature adipose tissue, devoid of neoplastic or cholesteatomatous features. At the 1-year postoperative follow-up, no evidence of recurrent middle ear mass was observed.

Discussion

Heterotopic salivary gland tissue (HSGT) is most frequently reported in the head and neck region, with documented cases involving the pituitary gland, external auditory canal, mastoid, thyroglossal duct, tongue, thyroid and its capsule, parathyroid glands, and sternoclavicular joint. Salivary gland choristoma of the middle ear remains exceptionally rare, with only approximately 50 cases reported since the initial description by Taylor et al in 1961. Epidemiologic analysis of these cases reveals characteristic features: a female predominance, unilateral involvement (left-to-right ratio ∼7:1), and an age range spanning from 9 months to 52 years. ² Notably, the current case involved a male patient within this age spectrum, presenting with unilateral left-sided disease, aligning with the established clinical profile of this entity.

Beyond the aforementioned epidemiological characteristics, middle ear salivary gland choristoma typically manifests as conductive hearing loss in the affected ear, accompanied by ossicular chain anomalies and a soft tissue density mass within the tympanic cavity on mastoid/temporal bone computed tomography (CT), with potential concurrent facial nerve paralysis. Notably, a subset of patients may present with concurrent congenital anomalies, including microtia, ³ alopecia, auricular swelling, external auditory canal malformations, ⁴ Dandy–Walker syndrome, ⁵ branchio-renal syndrome, ⁶ and developmental delays. Although the pathogenesis of middle ear salivary gland choristoma remains debated, accumulating evidence implicates aberrant differentiation of the first and second branchial arches during fetal development as a plausible mechanism. ⁷ In the current case, the patient exhibited left-sided conductive hearing loss, partial ossicular chain defects on mastoid CT, and a tympanic cavity soft tissue mass, aligning with typical clinical and imaging characteristics of this entity. However, no associated congenital anomalies were identified, underscoring that while embryogenic developmental anomalies are considered central to choristoma formation, concurrent congenital anomalies constitute non-obligatory features. This case provides novel evidence supporting the theory of pluritissular choristoma arising from localized embryogenic aberrations, emphasizing the clinical imperative to investigate potential composite malformations in cases of middle ear dysplasia.

The diagnosis of salivary gland choristoma of the middle ear currently lacks established diagnostic criteria. Given its non-specific clinical manifestations and exceptional rarity, careful differentiation from cholesteatoma is imperative during diagnostic evaluation to avoid misclassification. Thin-slice temporal bone CT remains the most widely used preoperative imaging modality; however, it lacks specificity in distinguishing soft-tissue density lesions. On temporal bone CT, cholesteatomas typically present as soft-tissue masses within the middle ear cavity and mastoid with adjacent bony erosion — a feature shared by granulomas, cholesterol granulomas, and chronic suppurative otitis media. ⁸ In this case, reliance solely on preoperative temporal bone CT led to diagnostic misclassification,as MRI was not performed initially due to the high clinical and radiological suspicion for congenital cholesteatoma, the most common cause of pediatric congenital conductive hearing loss, and the incremental value of DWI MRI was not fully appreciated at the time. Retrospective analysis of analogous cases indicates distinct MRI characteristics: middle ear cholesteatomas demonstrate T1-weighted isointensity/hypointensity, T2-weighted hyperintensity, and restricted diffusion (DWI hyperintensity), whereas salivary gland choristomas typically demonstrate T1-weighted hyperintensity, T2-weighted hyperintensity, and unrestricted diffusion (DWI hypointensity). ⁹ Together, these findings indicate that preoperative MRI with DWI sequence should be routinely added to temporal bone CT to improve diagnostic accuracy and prevent misdiagnosis in children with congenital middle ear soft-tissue lesions. Based on this evidence, preoperative temporal bone MRI may enhance diagnostic accuracy in differentiating these entities. Histopathological examination remains the gold standard for confirming salivary gland choristoma of the middle ear.

Although no reported cases or theoretical evidence suggest malignant transformation of middle ear salivary gland choristomas, surgical management must balance diagnostic confirmation with facial nerve preservation due to the tumor’s common proximity to the facial nerve. In this case, complete tumor excision was prioritized as the lesion showed no direct facial nerve involvement. Postoperatively, the patient exhibited no facial palsy, with sustained facial nerve integrity confirmed at 1-year follow-up. Concurrent ossiculoplasty with partial ossicular replacement prosthesis (PORP) implantation yielded favorable outcomes: hearing thresholds improved by 20 dB HL at 2 weeks post-surgery, with further audiological gains maintained at 1 year. Retrospective analysis of 11 similar cases performing ossiculoplasty^3,6,10-18 revealed hearing improvement in 6 patients.^12-16 For cases with stapedial anomalies precluding ossicular reconstruction, bone-anchored hearing aids (BAHA) remain a viable alternative.^6,17 Based on these findings, complete resection is strongly recommended for salivary gland choristomas without neural compromise, ¹⁹ as combined tumor excision and ossiculoplasty optimizes postoperative hearing rehabilitation and quality of life. ²

Notably, histopathological examination in this case revealed adipose tissue components within the lesion. Middle ear lipomas remain exceptionally rare, with only eight documented cases reported since the first description in 1985. Luetje et al identified fat deposition adjacent to the vertical segment of the facial nerve in the mastoid region in 17% of 240 cadaveric temporal bones, suggesting this anatomical distribution may represent a potential origin for lipomatous development. Tono et al further observed fibroconnective tissue interspersed with small adipocyte nests in fetal and pediatric epitympanic recess specimens, postulating that residual embryonic mesenchymal remnants might undergo adipose differentiation, thereby contributing to middle ear lipoma formation. Given the coexistence of salivary gland choristoma in this pediatric case, we hypothesize that concurrent ectopic implantation of both salivary gland precursors and adipocyte precursors during ossicular and facial nerve embryogenesis may lead to the development of this composite choristoma through postnatal differentiation processes.

Conclusion

This report details the first documented instance of coexisting salivary gland choristoma and lipoma within the middle ear, illustrating the diagnostic complexities inherent in pediatric conductive hearing loss of congenital origin. Preoperative assessment, relying exclusively on high-resolution computed tomography, initially misclassified the lesion as cholesteatoma—a limitation reflecting the modality’s inherent challenges in distinguishing soft-tissue pathologies. Definitive histopathology revealed benign ectopic salivary tissue admixed with mature adipocytes, suggestive of concurrent embryogenic aberrations during ossicular development. Complete microsurgical excision with tailored ossiculoplasty yielded substantial and sustained auditory gains, achieving a 20 dB HL improvement at one-year follow-up without recurrence or neural compromise. These findings advocate for incorporating diffusion-weighted magnetic resonance imaging as an adjunct diagnostic tool to improve differentiation from cholesteatoma, alongside a multidisciplinary paradigm emphasizing radical resection with functional preservation in managing embryological dysplasias.