A dermoid cyst in the fourth ventricle of an adult patient: a case description emphasizing diagnostic challenges and surgical management

Introduction

Intracranial dermoid cysts (IDCs) are rare, benign, congenital lesions caused by embryological malformations during neural tube closure (in the fifth to sixth gestational week) (1). In adults, IDCs frequently rupture, causing severe complications, including hydrocephalus and chemical meningitis (2). Thus, early, accurate diagnosis and surgical intervention are essential in clinical practice.

We present an exceptionally rare case of a fourth ventricular dermoid cyst initially misdiagnosed as an astrocytoma. Through retrospective analysis integrating preoperative imaging features with histopathological findings, this study systematically examined the diagnostic challenges of lipid-deficient dermoid cysts in the fourth ventricle. Our objectives were to delineate characteristic imaging patterns and optimize differential diagnostic strategies, ultimately enhancing preoperative diagnostic accuracy and informing surgical planning.

Case presentation

A 55-year-old male presented to our neurosurgery clinic with a 2-month history of persistent headaches and intermittent nausea without vomiting. Initial cranial computed tomography (CT) revealed a fourth ventricular cystic mass containing septations and calcifications (Figure 1A). Subsequent magnetic resonance imaging (MRI) revealed a fourth ventricular lesion with internal septations and peripheral cerebellar edema on axial T1/T2-weighted sequences (Figure 1B,1C), while diffusion-weighted imaging (DWI) showed no restricted diffusion (Figure 1D). Mild enhancement of septations and cyst walls was observed on post-contrast T1-weighted axial, coronal, and sagittal images (Figure 1E-1G). The radiographic features were initially interpreted as indicative of a low-grade astrocytoma.

Figure 1 Preoperative and postoperative imaging findings in a 55-year-old male. (A) An axial CT image showed a cystic mass in the fourth ventricle. (B,C) Axial T1- and T2-weighted magnetic resonance images showed a fourth ventricular lesion with internal septations (arrow) and (B) peripheral cerebellar edema. (D) DWI showed that there was no diffusion restriction in the lesion. (E-G) Axial, sagittal, and coronal contrast-enhanced T1-weighted images revealed subtle marginal enhancement. (H) A postoperative CT scan confirmed almost complete resection of the fourth ventricular tumor. (A,H) CT; (B-G) MRI. CT, computed tomography; DWI, diffusion-weighted imaging; MRI, magnetic resonance imaging.

Following unremarkable preoperative laboratory investigations, the patient underwent suboccipital craniotomy on February 12, 2025. Postoperative CT (Figure 1H) confirmed near-complete resection with only minimal residual cyst wall remaining. During surgery, surgeons identified abundant keratinized material in the lesion (Figure 2A). Histopathological analysis (Figure 2B,2C) established the definitive diagnosis of a dermoid cyst. The cyst wall was lined by keratinizing stratified squamous epithelium and contained skin adnexal structures, including sebaceous glands, representing ectodermal derivatives. The adjacent stroma showed scattered small vascular structures and focal lymphocytic infiltration, indicating limited mesodermal components. The cyst lumen was filled with lamellated keratinous debris.

Figure 2 Gross and histopathological findings of a fourth ventricular dermoid cyst. (A) Intraoperative view during posterior fossa craniotomy showed a cystic cavity filled with keratinous material (arrow). (B) The cyst wall was lined by keratinizing stratified squamous epithelium (arrow), and the lumen contained lamellated keratinous debris (double arrow). Focal lymphocytic infiltration was present in portions of the cyst wall (hollow arrow). (C) In another representative area, skin adnexal structures were identified in the cyst wall, including lobules of mature sebaceous glands (arrow). The adjacent stroma contained vascular structures (hollow arrows). Scale bar =100 µm; hematoxylin and eosin staining (B,C).

All the procedures in this case were performed in accordance with the ethical standards of the institutional and/or national research committee(s), and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this article and the accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Dermoid cysts are congenital developmental lesions that arise from the sequestration of surface ectoderm during embryonic fusion, resulting in cysts that contain skin adnexal structures and occasionally mesodermal elements. These rare entities constitute 0.04–0.7% of all intracranial neoplasms (3) and demonstrate a slight male predilection with a bimodal age distribution, predominantly affecting children <10 years and adults aged 30–50 years (4,5). Notably, our 55-year-old patient falls outside this predominant age distribution, representing an atypical presentation that expands current epidemiological understanding.

Dermoid cysts typically exhibit indolent growth with benign biological behavior, though rare malignant transformation has been documented (1). These lesions demonstrate heterogeneous clinical manifestations, with literature-reported incidence rates of 32.6% for seizures, 26.5% for headaches, and 16.3% for cerebral ischemic events presenting with sensorimotor deficits (6). Cyst rupture may precipitate chemical meningitis characterized by signs of meningeal irritation (7). The patient in this case presented solely with a headache, attributable to fourth ventricular obstruction by the tumor mass. This anatomical compromise resulted in obstructive hydrocephalus and subsequent intracranial hypertension due to cerebrospinal fluid pathway disruption.

IDCs predominantly localize to the posterior fossa, affecting approximately two-thirds of cases, with a predilection for the midline and paramedian cerebellar regions (8,9). Other reported sites include subdural/extradural occipital spaces, pontine areas, frontal lobe surfaces, and parasellar/sellar regions (10,11). Ventricular involvement is exceptionally rare, with only one prior case documented in the third ventricle (12), and only one case reported in the fourth ventricle exhibiting characteristic fatty components (13). Notably, the present case constitutes the first reported instance of a radiologically fat-deficient dermoid cyst confined to the fourth ventricle, expanding both the topographic spectrum and imaging diagnostic considerations for these lesions. Table 1 summarizes the basic clinical information of previously reported cases of IDCs in the ventricles.

Histopathological confirmation remains definitive for IDCs, classically demonstrating a stratified squamous epithelial lining with associated cutaneous adnexa (sebaceous glands, hair follicles, and eccrine structures) and vascular networks, accompanied by pathognomonic luminal contents, including adipose tissue, cholesterol crystals, keratin debris, and hair shafts, often with calcifications (14). In the present case, microscopic examination demonstrated cyst walls lined by keratinizing stratified squamous epithelium with skin adnexal structures, including sebaceous glands, along with scattered small vascular structures (Figure 2B,2C). The cyst lumen contained lamellated keratinous debris. No definite adipose tissue was identified in the examined sections, and focal peripheral lymphocytic infiltration suggested an associated inflammatory response. These histopathological findings were consistent with the imaging findings.

IDCs are radiologically characterized as midline round or oval lesions with viscous fluid and fatty components, classically demonstrating hypodensity on CT, T1 hyperintensity, well-defined margins, and non-enhancement (6,15-17). In this case, the preoperative misdiagnosis of an astrocytoma arose from four atypical features: (I) inflammatory adhesions mimicking cerebellar vermis parenchymal tumors; (II) cystic architecture with septations, calcified walls, and mild enhancement overlapping with low-grade gliomas (18); (III) perilesional edema suggestive of infiltrative growth; and (IV) the absence of radiographic fat/cholesterol content.

Postoperative analysis integrating histopathological and imaging data provided five critical insights: (I) anatomic predilection: the fourth ventricle’s midline location aligned with dermoid cyst pathogenesis, despite being reported only once previously (13); (II) vascular correlation: histologically confirmed microvasculature in cyst walls (Figure 2B) corresponded to observed mild enhancement, consistent with Onoda and Neugroschl’s findings (19,20); (III) inflammatory pathogenesis: adhesion and perilesional edema reflected inflammatory infiltration, as documented by Wang et al. (21); (IV) calcification mechanism: Watanabe et al.’s model of calcium deposition in dermal appendages supported the consideration of dermoid cysts in calcified midline cysts (22,23); and (V) microscopic fat: no microscopic adipocytes were identified in our specimen (Figure 2B), in contrast to previous reports describing fat below imaging detection thresholds (24,25). These findings have important clinical implications. Specifically, fourth ventricular cystic lesions exhibiting septal calcification, mild enhancement, and ill-defined margins—even without microscopic fat—require the inclusion of lipid-deficient dermoid cysts in differential diagnoses. Preoperative recognition enables optimized surgical strategies to mitigate chemical meningitis risks and improve patient outcomes.

Fourth ventricular cystic masses with calcification require differentiation from dermoid cysts among tumors such as epidermoid cysts, low-grade astrocytomas, rosette-forming glioneuronal tumors (RGNTs), ependymomas, and neurocysticercosis. Epidermoid cysts, which are more common than dermoid cysts in this region, exhibit “growth-along-cleft” patterns, typically demonstrating restricted diffusion (DWI hyperintensity) and variable T1 hyperintensity due to cholesterol or protein-rich contents—features absent in dermoid cysts (26). Low-grade astrocytomas often display cystic degeneration and mural calcification secondary to vascular degeneration, with mild enhancement that can overlap with lipid-poor inflammatory dermoid cysts, complicating differentiation (27). RGNTs frequently manifest as multi-cystic lesions in the fourth ventricle, often with calcification and characteristic “pepper-like” transverse-layered enhancement, differing from dermoid cysts in enhancement patterns (28). Ependymomas, which primarily affect children, show downward “plastic” growth in the fourth ventricle and moderate enhancement, differing from dermoid cysts in both growth pattern and enhancement degree (29). Neurocysticercosis, associated with undercooked meat consumption, presents as intraventricular calcified cysts with vascularized walls, prominent perilesional inflammation, moderate mural enhancement, and severe edema, facilitating differentiation via clinical history and imaging findings (30).

The therapeutic goal for dermoid cysts is complete surgical resection of the cyst wall and contents. MRI plays a critical role in delineating lesion extent and neurovascular relationships, enabling the preoperative evaluation of radical resection feasibility (31,32). Standard surgical protocols involve cyst wall incision for intracapsular decompression, followed by microsurgical dissection of the cyst wall from adherent neurovascular structures (32,33). When dense adhesion between the tumor capsule and critical neural/vascular tissues occurs, subtotal resection with residual adherent fragments is recommended to minimize iatrogenic complications (31,32,34). In the present case, subtotal resection was performed via a suboccipital craniotomy with an obex approach due to brainstem adherence, preserving functionally critical regions. Postoperative recovery featured significant headache alleviation and the absence of IDC recurrence on follow-up CT, with no clinical evidence of brainstem dysfunction to date.

Conclusions

Fourth ventricular dermoid cysts are extremely rare and may present without obvious macroscopic fat, leading to diagnostic confusion with other cystic tumors of the posterior fossa. In the present case, the combination of a calcified, multiloculated cystic lesion, mild enhancement, and absence of diffusion restriction was ultimately decisive for the correct diagnosis. A “lipid-deficient” dermoid cyst should thus be considered in the differential diagnosis of atypical fourth ventricular masses, especially when imaging and clinical findings are discordant. Early recognition of this entity can improve preoperative counseling, guide the extent of surgical resection, and help minimize procedure-related complications such as chemical meningitis.

Acknowledgments

None.

Footnote

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1-2748/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this case were in accordance with the ethical standards of the institutional and/or national research committee(s), and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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