Infiltrating Lateral Skull Base Pleomorphic Adenoma with Lower Cranial Nerve Palsies: A Case Report and Literature Review of a Rare Entity
Kalpesh Hathi MD* 1, Reshma Ghedia MBBS 1, Bullock M MD, FRCSC 2, Taylor SM MD, FRCSC 1, Nael Shoman MD, FRCSC 1
*Correspondence to: Kalpesh Hathi MD, Division of Otolaryngology – Head and Neck Surgery, Halifax. Nova Scotia, Canada, QEII Health Sciences Centre, 3rd Floor Dickson Building, 5820 University Avenue, Halifax, Nova Scotia, Canada, B3H 1Y9.
Copyright.
© 2026 Kalpesh Hathi, This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received: 29 July 2026
Published: 11 August 2026
DOI: https://doi.org/10.5281/zenodo.21886974
Abstract
A 42-year-old man with a previous benign parotid mass resection, presented with ipsilateral cranial nerve VII, VIII, X, and XII palsies. MRI revealed a 7.5x4.1x2.5 cm mass involving the deep parotid, pre-styloid parapharyngeal space, jugular foramen, petrous apex, and internal auditory canal.
The patient underwent mastoidectomy, petrous apicotomy, and biopsy of skull base mass. Histology was consistent with pleomorphic adenoma. The imaging, cranial palsies and rapid progression were concerning for malignancy, and multidisciplinary discussion felt this to represent carcinoma ex-pleomorphic adenoma (CXPA). Treatment with radiotherapy was initiated.
This case highlights an unusual anatomical spread of a salivary gland tumour extending to the skull base and presenting with lower cranial nerve palsies.
Introduction
Most parotid masses are benign (~75-80%) [1]. Pleomorphic adenoma (PA) is a benign salivary gland tumour and accounts for ~70% of benign parotid masses [1,2].
Carcinoma ex-pleomorphic adenoma (CXPA) is an epithelial or myoepithelial malignancy arising from the malignant transformation of a previously benign PA [3]. The risk of malignant transformation to a CXPA is low at ~2-5% [3]. CXPA often develops as a rapid increase in growth of a previous PA, or as a recurrence of the mass following PA resection or previous radiotherapy, and rarely de novo [4].
Only one previous report of a destructive lateral skull base benign PA without cranial nerve involvement is published [7].
Case Presentation
An otherwise previously healthy 42-year-old man was referred to the otolaryngology-head and neck surgery for left-sided hearing loss and tinnitus over the past two months. This was followed by rapid progression to vertigo, imbalance, headaches, and left-sided facial nerve palsy progressing quickly over two to four days. The patient had a history of imaging and an FNA for a benign parotid mass, leading to a partial parotidectomy and lymph node resection in a different country one year prior. His post-operative course was uneventful.
On examination, he had a left lower motor facial palsy graded as House-Brackmann grade 5/6. A Weber’s tuning fork test lateralized to the right, suggesting a sensorineural hearing loss on the left side, which along with his history of vertigo, was in keeping with a vestibulocochlear palsy. He also had left hypoglossal palsy with his tongue deviating towards the ipsilateral side. Further, he had an absent gag reflex.
Upper airway flexible endoscopy showed no nasopharyngeal lesion and an immobile left vocal cord in keeping with left vagus nerve involvement. He had evidence of a previous modified Blair incision and no palpable cervical lymphadenopathy. Micro-otoscopy revealed a normal external auditory canal and tympanic membrane with no middle ear effusion.
The patient initially underwent a CT scan which showed a large, heterogeneously enhancing soft tissue mass centered at the left petrous apex, extending inferiorly and posteriorly involving the occipital bone and superiorly reaching the internal auditory canal (Figure 1). The mass was visible in the posterior parotid and through the stylomandibular tunnel into the pre-styloid parapharyngeal space. There was thinning and dehiscence of the carotid canal. The tumour did abut the left cerebellar hemisphere and the posterior aspect of the left cavernous sinus, without infiltration. No cervical lymphadenopathy was identified.
Following this, a multiplanar-enhanced MRI was performed, demonstrating an isointense mass on T1 imaging, which was heterogeneous but predominantly dark on T2 (Figure 2). The study also showed the tumour extending into the deep parotid lobe and herniating into the pre-styloid parapharyngeal space. The mass was 7.5x4.1x2.5 cm in size. The tumour was present below the stylomastoid foramen (causing CN VII palsy), extended into the internal auditory canal (causing CN VIII palsy), the jugular foramen (causing CN X palsy) and the hypoglossal canal (causing XII palsy). The low signal intensity, destructive pattern was compatible with a malignant parotid tumor consistent with T4bN0 radiological staging.
Given the location of this tumor extending laterally within the temporal bone, we elected to obtain tissue from the petrous apex portion of this lesion via an infra-labyrinthine retro-facial approach. Intra-operatively, a friable mass with a flesh-like appearance and mild vascularity was encountered, and multiple tissue pieces were taken for pathological diagnosis (Figure 3).
The pathology results suggested a PA, consisting of myxoid/chondromyxoid stroma and an epithelial component of the epithelial and myoepithelial cells with tubule formation. No significant atypia, mitotic activity, or necrosis (Figure 4a-c).
The patient tolerated the biopsy well, had no adverse effects and is currently undergoing radiotherapy, which is being tolerated well.
Discussion
This case highlights the diagnostic challenge associated with CXPA. CXPA is found within salivary tissue, which is a combination of both benign PA and CXPA components, and the exact proportion of each varies [1-3]. Thus, when taking biopsies of these masses, the pathology may return as PA; however, this may be due to the biopsy targeting a foci of benign tissue or missing foci of carcinoma [8]. It is important to consider the clinical presentation; in this case, the destructive nature of the lesion and cranial nerve involvement led to a multidisciplinary team favouring a diagnosis of CXPA.
A literature search revealed only one previous case of an invasive lateral skull base benign PA without cranial nerve involvement; this is the first CXPA of this nature reported [7]. In the previous case, the tumour was managed surgically [7]. In the present case, the rapid progression with multiple lower cranial nerve involvement galloping within two months was highly in keeping with an aggressive malignant tumor. We employed a surgical approach to obtain tissue for diagnosis and then the patient underwent radiation therapy for definitive management to avoid any delay for further tissue sampling of a lesion that, if malignant was non-operable due to the tumor extending within the petrous apex, abutting the lower cranial nerves and neurovasculature, making an intent at curative surgery unrealistic, with a high risk of morbidity. Radiotherapy as a nonsurgical modality has been shown to be effective in controlling or curing recurrent tumours in patients with a high risk of further recurrence [9,10].
References