Ascending Perineural Spread of a Parotid Gland Adenoid Cystic Carcinoma Masquerading as a Local Recurrence of Skull Base Meningioma - Illustrative Case

Sep 29, 2026

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Skull base lesions form a complex interface where both intracranial and extracranial diseases may present, and extracranial tumors can mimic primary intracranial pathology. This case describes a 48-year-old woman with progressive right facial palsy and a remote history of tentorial meningioma resection. Imaging showed a residual tentorial meningioma and a homogeneously enhancing mass extending along the facial nerve without apparent parotid enlargement. Multiple biopsies identified adenoid cystic carcinoma originating from the parotid gland, managed with carbon-ion radiation therapy, with stability for 28 months post-surgery.

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CategoryHealthcare

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Case Report

NMC Case Report Journal 12, 541-545, 2025 Ascending Perineural Spread of a Parotid Gland Adenoid Cystic Carcinoma Masquerading as a Local Recurrence of Skull Base Meningioma: Illustrative Case Daisuke SATO,1 Satoru MIYAWAKI,1 Satoshi KIYOFUJI,1,2 Takuya YOSHIDA,1 Yudai HIRANO,1 Atsuhito NAKAYAMA,3 Masaki SUZUKI,3 Yuki SAITO,4 Taichi KIN,1,5 and Nobuhito SAITO1 1 Department of Neurosurgery, The University of Tokyo Hospital, Tokyo, Japan 2 Department of Neurosurgery, Fuji Brain Institute and Hospital, Fujinomiya, Shizuoka, Japan 3 Department of Pathology, The University of Tokyo Hospital, Tokyo, Japan 4 Department of Otolaryngology, The University of Tokyo Hospital, Tokyo, Japan 5 Department of Medical Information Engineering, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan Abstract The skull base is an intricate interface between the cranium and the face. Both intracranial and extracranial pathologies can occur at this location. Although the tumor origin is clear in most cases, certain extracranial tumors may mimic primary intracranial pathologies. A 48-year-old woman with a history of resection of a right tentorial meningioma 17 years earlier presented with worsening right facial palsy. No obvious enlargement of the parotid gland was noted. Imaging revealed a residual tentorial meningioma and a homogenously enhancing mass extending alongside the right facial nerve. The patient underwent several biopsies, and the diagnosis of adenoid cystic carcinoma arising from the parotid gland was made. She subsequently underwent carbon-ion radiation therapy and remained stable for 28 months after surgery. The representative case reiterates the importance of evaluating both intracranial and extracranial pathologies when a clinician encounters skull base tumors, especially those with perineural spreading. The tendency of meningiomas to involve the trigeminal nerve while sparing the facial nerve may provide a clue for the differential diagnosis. Keywords: parotid gland tumor, adenoid cystic carcinoma, perineural invasion, ascending perineural spread, meningioma Introduction The skull base represents the inferior aspect of the neurocranium and serves as an interface between the extracranial and intracranial compartments.1,2) Hence, not only do primarily intracranial pathologies involve the skull base, but extracranial pathologies may also invade and traverse the skull base, spreading intracranially.2) Adenoid cystic carcinoma (ACC) is a rare malignant tumor of extracranial origin that primarily involves the salivary glands.3) Biphasic glandular structures composed of abluminal myoepithelial cells and luminal ductal cells are characteristic of ACC.3-5) ACC demonstrates indolent, locally invasive growth with a high propensity for locoregional recurrence and metastasis.6-8) Although local temporal bone invasion by ACC has been described repeatedly,9-11) cases of ACC presenting as a solid intracranial mass are rarely reported, as far as our search revealed. We encountered a case of an occult parotid gland tumor without apparent enlargement, traveling along the facial nerve and presenting as a skull base tumor. Because the patient had previously undergone resection of a tentorial meningioma several years earlier, and swelling of the parotid gland was not evident, recurrence of the men- Received July 2, 2025; Accepted September 7, 2025 Copyright Ⓒ 2025 The Japan Neurosurgical Society This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives International License. 542 D. Sato et al. Fig. 1 MRI revealed a right tentorial meningioma (A). A slight residual tumor was observed after resection (B). Subtle regrowth of the residual tumor was noted 17 years after the initial surgery (C). A homogenously enhancing lesion (white arrow) involved the arcuate eminence (D) and extended along the facial nerve (E). The tumor (white arrow) extension reached the parotid gland (

FAQs

Why can an extracranial tumor mimic an intracranial skull base lesion?

The skull base is an interface between intracranial and extracranial compartments, so extracranial pathologies may invade and traverse it while spreading intracranially, imitating primarily intracranial disease.

What clinical presentation led to suspicion in this case?

The patient developed worsening right facial palsy over several months, with severe dysfunction of the right facial nerve and facial asymmetry, prompting neuroimaging and further evaluation.

How was the diagnosis of adenoid cystic carcinoma established despite no parotid enlargement?

Imaging showed a mass extending along the facial nerve and reaching the parotid gland without apparent parotid enlargement; multiple biopsies ultimately confirmed adenoid cystic carcinoma arising from the parotid gland.

Sep 29, 2026

Uploaded by Jiven