2026 Volume 13 Pages 77-84
Choroid plexus cysts are typically benign lesions found within the ventricular system during prenatal imaging and are usually asymptomatic. Intraparenchymal choroid plexus cysts, especially in adults, are exceptionally rare, with very few reported cases. This case report aims to present a rare instance of a symptomatic, intraparenchymal choroid plexus cyst in an adult patient and to discuss the diagnostic and surgical considerations involved. We present the case of a 50-year-old man with complaints of lower extremity weakness and imbalance who was found to have a bilobulated cyst in the frontal cortex causing significant mass effect and midline shift. The patient underwent cyst fenestration through endoscope-assisted open craniotomy, with marked postoperative reduction in cyst size and resolution of neurological symptoms. Histopathology confirmed the diagnosis of a choroid plexus cyst. This case highlights the importance of considering rare pathologies such as choroid plexus cysts in the differential diagnosis of cystic brain lesions with mass effect in adults.
The choroid plexus is a tissue of the central nervous system composed of blood vessels lined by specialized epithelium made up of ependymal cells. It resides within the ventricular system of the brain, particularly in the innermost meningeal layer, the pia mater. The choroid plexus has many functions, including, but not limited to, the production of cerebrospinal fluid (CSF) and contribution to the formation of the blood-CSF barrier.1) The choroid plexus has components that derive from 2 embryonic origins, the neuroectoderm and mesoderm.1) Like many tissues in the body, the neuroectoderm can sometimes develop cysts, which are fluid-filled sacs that can develop due to a variety of causes, including obstruction, injury, tumors, and many more. These cysts are often benign but can produce a significant intracranial mass effect. Neuroectodermal cysts include arachnoid cysts, choroid plexus cysts (CPCs), and glioependymal/ependymal cysts.2) CPCs are small fluid-filled sacs containing CSF and are among the most common congenital abnormalities of the choroid plexus.3) In adult patients, diagnosis usually follows the incidental discovery of CSF density on computed tomography (CT) or magnetic resonance imaging (MRI).2,4) The differential diagnosis of these cysts includes ependymal cysts, epidermoid cysts, arachnoid cysts, porencephalic cysts, villous hyperplasia of the choroid plexus, subacute in-utero intraventricular hemorrhage, and hydatid cysts secondary to echinococcal infection.5,6) Since the choroid plexus resides within the ventricles of the brain, its cysts are typically expected to occur somewhere throughout the ventricular system, most commonly in the glomus of the lateral ventricles.3) These lesions are typically benign and asymptomatic but, in rare cases, may present with symptoms later in life, with some documented cases reporting symptoms at 30, 60, and 65 years of age.7) Due to the exceedingly low prevalence of these cysts, information regarding typical management approaches is scarce.
We report a 50-year-old male factory worker with hypertension who presented with a 7-8-month history of left-sided limb weakness and tremor, and progressive imbalance for the past 3-4 months. Neurological examination revealed mild left lower extremity weakness (4/5); the physical exam was otherwise unremarkable. A non-contrast head CT revealed a bilobular cystic mass with CSF-like density measuring approximately 62 × 52 × 55 mm located in the right frontal cerebral cortex, causing a 15 mm leftward midline shift (Figure 1A and B). MRI similarly revealed 2 adjacent cystic lesions in the right frontal region (Figure 2A-D). The preliminary differential diagnosis included porencephalic cyst, arachnoid cyst, choroidal cyst, and hydatid cyst. These findings were further evaluated using MR cisternography (Figure 3A-D). The external orientation of the choroid plexus and eventual protrusion out of the ventricular system is believed to underlie the cyst's development (Figure 3A). The patient underwent endoscope-assisted open craniotomy with intraoperative neuromonitoring for cyst resection and fenestration. Under general anesthesia, the patient was positioned supine with the head rotated 90°, and an inverted question mark-shaped skin incision was made. A frontoparietal craniotomy was performed due to the preliminary diagnosis of a hydatid cyst, which could not be definitively diagnosed preoperatively. We avoided retraction of the brain to access and remove the cyst with the walls intact and instead used an endoscope for access and fenestration. This was only done after direct visualization confirmed the cyst was not hydatid. Although neuroendoscopy is commonly used for CSF circulation disorders, intracranial cysts, and tumors, it is inappropriate for hydatid cysts because rupture may cause dissemination, recurrence, or anaphylaxis.8,9) An open craniotomy was therefore the best initial approach to ensure safe exposure and prevent inadvertent rupture during exploration. Using neuronavigation and intraoperative ultrasound, the cyst was localized, and its walls were dissected under the microscope. No evidence of echinococcal infection was found. Adherent portions of the cyst wall were biopsied, the remaining tissue was coagulated, and both cysts were fenestrated. An ostomy was created into the lateral ventricle, and CSF flow was confirmed endoscopically. All layers were closed anatomically. Postoperative (Post-op) MRI showed a reduction of the cyst to 53 × 43 × 52 mm, a 5 mm decrease in midline shift, and communication between the cyst lumen and the ventricle (Figure 2), with regression of mass effect. On post-op day 28, neurological examination was normal with no residual deficits. Histopathological examination revealed a cyst wall composed of a single layer of flattened cuboidal epithelial cells adjacent to glial parenchyma (Figure 4). Immunohistochemistry showed diffuse pancytokeratin and S100 positivity (Figure 5A and B), consistent with an epithelial origin and suggestive of choroid plexus differentiation. Cyst-lining cells were negative for glial fibrillary acidic protein (GFAP) and epithelial membrane antigen (EMA), helping to exclude a glial or ependymal origin. No features of malignancy were identified, and the Ki-67 index was low. Overall findings were consistent with a CPC. On post-op day 27, non-contrast CT revealed marked cyst reduction. Written informed consent has been obtained from the patient to publish this paper.
Non-contrast axial (A) and coronal (B) CT images of the head showing a large, bilobulated cystic lesion in the right frontal lobe measuring approximately 62 × 52 × 55 mm (AP × T × CC), with CSF-like density and no internal enhancement. The lesion exerts significant mass effect on the surrounding parenchyma, compresses the right lateral ventricle, and results in a 15 mm leftward midline shift.
CT: computed tomography; CSF: cerebrospinal fluid
Preoperative axial (A) and coronal (B) T2-weighted MRI scans revealing two adjacent, well-demarcated cystic structures in the right frontal cerebral cortex. The cysts demonstrate hyperintense signals consistent with CSF, with marked mass effect including compression of the right lateral and third ventricles, and a midline shift similar to that seen on CT. Postoperative axial (C) and coronal (D) T2-weighted MRI scans taken on post-op day 1, showing reduced cyst dimensions (53 × 43 × 52 mm) and decreased midline shift (10 mm). Communication between the cyst and the lateral ventricle is visible, confirming the success of the fenestration.
CT: computed tomography; MRI: magnetic resonance imaging; CSF: cerebrospinal fluid
Cisternography images in the axial (A and B), coronal (C), and sagittal (D) planes. Image (A) shows the contiguous relationship between the cyst (red arrow) and the ventricular system (black asterisks). The choroid plexus (yellow arrow) can be seen extending in the direction in which the cyst grew.
High magnification (×200) H&E stain depicting the cyst wall lined by a single layer of flattened, cuboidal epithelial cells characteristic of choroid plexus epithelium.
H&E: hematoxylin and eosin
Immunohistochemical staining with Pan-Cytokeratin (A) and S100 (B) showing diffuse cytoplasmic positivity in the cyst-lining epithelial cells.
CPCs are typically benign, intraventricular lesions discovered incidentally, particularly in pediatric patients.10,11) However, ectopic intraparenchymal cysts are exceedingly rare. A summary of reported CPC cases is available in Table 1.7,12,13) Azzam et al.12) described a similar supratentorial, non-ventricular cyst in an adult, lined partially by choroid plexus tissue, confirming the possibility of ectopic origins. Like their case, our lesion exhibited no ventricular communication, emphasizing the need to consider intraparenchymal CPCs in atypical locations. Radiologically, CPCs often mimic CSF on both CT and MRI.10,11) In one 53-year-old patient, a cyst obstructing the foramen of Monro appeared CSF-isointense on T1 and hyperintense on T2, a finding attributed to protein content.10) This mirrors our patient's imaging, which was iso- to hyperattenuating on CT and CSF-like on MRI. These imaging characteristics are nonspecific and may resemble a variety of other intracranial lesions, including arachnoid cysts, ependymal cysts, neuroglial (glioependymal) cysts, hydatid cysts, cystic neoplasms or metastases, among others. The diagnosis of CPCs with imaging alone is therefore challenging, and immunohistochemical staining plays an essential role in reaching a definitive diagnosis. A summary of immunohistochemical and histopathological differences between CPCs and other cystic lesions is available in Table 2.2,14-19) The lining of CPCs stains similarly to normal choroid plexus epithelium, positive for vimentin, cytokeratin, S100, transthyretin, and synaptophysin, and negative for GFAP and EMA.2) This is consistent with the immunohistochemical profile seen in our patient's case, whose biopsy results were positive for cytokeratin and S100 (Figure 5), but negative for GFAP and EMA. Symptomatic cases may progress to hydrocephalus or focal mass effect requiring intervention. Jeon et al.11) reported a large intraventricular CPC successfully treated with neuroendoscopic fenestration in a young adult, recommending minimally invasive surgery as first-line when feasible. In our case, concerns about a possible hydatid cyst and the lesion's bilobulated, frontal-parenchymal location led us to choose an open microsurgical fenestration. This approach allowed safe drainage and decompression, resulting in rapid neurological improvement and a favorable radiologic outcome. Unlike most reported CPCs, which are small, incidental, and intraventricular, our case involved a symptomatic, bilobulated, intraparenchymal CPC in an adult, causing midline shift and motor deficits. Such a presentation aligns with Azzam's adult ectopic cyst12) but is unique in terms of morphology, location, and outcome. To date, only a handful of intraparenchymal CPCs have been reported in the literature. Our case appears to represent one of the largest documented intraparenchymal CPCs with frontal-lobe localization and symptomatic mass effect, based on available case literature.12,20) Numerous publications discussing extraventricular or intraparenchymal choroid plexus abnormalities are available; however, this literature is primarily composed of research around choroid plexus neoplasms, namely papillomas21-31) and carcinomas,32-35) not cysts. Several cases have been reported of intraparenchymal cysts that contained ectopic choroid plexus, but were not classified as CPCs.36-39) Intramedullary spinal CPCs have also been reported in the literature.40,41)
Summary of Other Reported Choroid Plexus Cysts (CPCs) (7,12,13)
| Reported cases | Patient | Clinical Presentation | Size | Location | Histopathology | Immunohistochemistry |
|---|---|---|---|---|---|---|
| GFAP: glial fibrillary acidic protein; EMA: epithelial membrane antigen | ||||||
| Intraparenchymal Choroid Cyst, 1990 (13) | 74-year-old woman | Progressive cognitive, gait disturbance, right-sided weakness. | 3 × 4 cm | Left frontoparietal region | Cyst wall lined by cuboidal, non-ciliated epithelium with small papillae and small clusters of vessels. | Not reported |
| Intracerebral cyst due to ectopic choroid plexus: case report, 1981 (12) | 32-year-old woman | Increased temporal lobe epilepsy episodes, two major nocturnal seizures. | Not reported | Right frontotemporal region | The cyst wall is lined in part by a thin band of poorly myelinated white matter and in part by flattened/cuboidal epithelium. | Not reported |
| Extraventricular choroid cysts, 1993 (7) | 38-year-old woman | 3-year history of worsening right-sided headaches, episodes of loss of consciousness, and volitional tremor of the left hand. | Not reported | Right parieto-occipital region | Cyst wall lined by flat non-ciliated cuboidal epithelium with occasional intracellular vacuolization. | Positive markers: cytokeratin, S-100, vimentin, EMA, and prealbumin. Negative markers: GFAP. |
| Extraventricular choroid cysts, 1993 (7) | 60-year-old man | Progressive right hemiparesis; pronounced spastic paresis of the right limbs. | Not reported | Left parietal lobe | ||
| Extraventricular choroid cysts, 1993 (7) | 65-year-old woman | One-month history of instability, left hemiparesis; examination showed spastic paresis of the left limbs and left homonymous hemianopsia. | Not reported | Right parieto-occipital region | ||
Comparison of Clinical and Imaging Differences with Other Cystic Lesions (2,14-19)
| Pathology | Origin | Histopathology | Immunohistochemistry | Imaging characteristics | Clinical presentation |
|---|---|---|---|---|---|
| CPC: choroid plexus cyst; CSF: cerebrospinal fluid; CT: computed tomography; DWI: diffusion-weighted imaging; EMA: epithelial membrane antigen; FLAIR: fluid-attenuated inversion recovery; GFAP: glial fibrillary acidic protein; GMS: Grocott-Gomori methenamine silver; ICH: intracranial hemorrhage; ICP: intracranial pressure; MRI: magnetic resonance imaging; N/A: not applicable | |||||
| Choroid Plexus Cyst (CPC) | Cyst of the choroid plexus containing CSF (2). | Cyst wall lined by cuboidal to columnar epithelium (2). | Positive markers: vimentin, cytokeratin, S-100, transthyretin, synaptophysin. Negative markers: EMA, GFA (2). | CT/MRI: CSF density/ signal (2). | Common in fetuses (associated with trisomy 18). Usually asymptomatic; may cause hydrocephalus. Incidental in adults (2). |
| Epidermoid cyst | Inclusion of ectodermal elements during neural tube closure (17). | Cyst lined by stratified squamous epithelium (18). | Keratin markers are positive, but staining is not needed for diagnosis (18). | CT/MRI: CSF-like density/signal. MRI (DWI): restricted diffusion (key distinguishing feature) (17). | Slowly expanding mass; headaches(most common), cranial nerve deficits, cerebellar signs, raised ICP (17). |
| Arachnoid cyst | Arachnoid membrane (2) | CSF-filled spaces lined by meningothelial cells and an outer collagenous membrane (2). |
Positive markers: EMA. Negative markers: cytokeratin, GFAP, transthyretin, synaptophysin (2). | MRI (FLAIR/DWI): low signal; no enhancement (2). | Often asymptomatic. Headache most common; it may cause hydrocephalus or nonspecific mass-effect symptoms (2). |
| Ependymal cyst | Neuroepithelial cysts lined by ependymal cells (16). | Ciliated or attenuated ependymal lining resting on a fibrous layer (16). | Positive markers: GFAP, S-100. Negative markers: EMA, cytokeratin, carcinoembryonic antigen (16). | CT: hypodense, well-circumscribed cyst. MRI: large unilocular cyst; isointense to CSF on T1-weighted images and FLAIR, hyperintense on T2-weighted images; no enhancement (16). | Mostly asymptomatic and discovered incidentally. The most common symptom is headache (16). |
| Porencephalic cyst | CSF accumulation within the brain parenchyma (15). | CSF-filled hemispheric cavity lined by gliotic white matter, no epithelial lining (15). | N/A | CT: well-defined hypodense cyst. MRI: CSF-signal cavity with gliotic wall/gliosis (15). | Cerebral palsy, seizures, intellectual disability, learning difficulties (neuronal loss), raised ICP, focal deficits, etc (15). |
| Hydatid cyst | Echinococcus granulosus infection (19). | Cyst wall with outer acellular laminated membrane, germinal membrane, and protoscolices(which contain hooklets) attached to the membrane (14). | Positive markers: hooklets are acid-fast positive on Ziehl-Neelsen stain; hooklets also stain with GMS (14). | MRI: well-circumscribed spherical non-enhancing intra-axial cyst containing CSF-isointense fluid. | Symptoms depend on size and location: focal neurological deficits, headaches, raised ICP, hydrocephalus, and papilloedema (19). |
In summary, this case reinforces the importance of including CPCs in the differential diagnosis of cystic, CSF-like brain lesions located outside the ventricular system, even in adults. When symptomatic or causing mass effect, timely surgical intervention, whether endoscopic or open, can yield excellent outcomes. Our experience suggests that image-guided fenestration or resection is an effective treatment strategy in such contexts, provided histopathological confirmation is obtained.
ConclusionsThis case highlights the diagnostic challenge and clinical importance of recognizing CPCs as a rare cause of mass effect in adult patients, particularly when located outside the ventricular system. While CPCs are typically benign and intraventricular, this report adds to the limited literature on symptomatic intraparenchymal CPCs in adults. In such presentations, neuroimaging alone may be insufficient for diagnosis, and histopathological confirmation is essential. Surgical intervention, whether endoscopic or open, can lead to excellent functional and radiological outcomes when performed in a timely manner. Clinicians should include CPCs in the differential diagnosis of large, CSF-like parenchymal lesions, especially in patients presenting with unexplained neurological deficits.
Conception or design of the work: Berkay Ayhan, Hüseyin Ömer Semiz, Zeyad Kamar
Data collection: Berkay Ayhan, Zeyad Kamar
Data analysis and interpretation: Hüseyin Ömer Semiz, Zeyad Kamar, Ülker Karagece Yalçın, Tuğçe Aycan Akbal Ersöz
Drafting the article: Zeyad Kamar
Critical revision of the article: Berkay Ayhan, Hüseyin Ömer Semiz
Patient management, surgical planning, and execution: Berkay Ayhan, Hüseyin Ömer Semiz
Other (study supervision, funding, materials, etc): Ülker Karagece Yalçın, Tuğçe Aycan Akbal Ersöz
All authors (Berkay Ayhan, Hüseyin Ömer Semiz, Zeyad Kamar, Ülker Karagece Yalçın, Tuğçe Aycan Akbal Ersöz) reviewed the results and approved the final version of the manuscript.
All authors have no conflict of interest.
Ethics Approval: No institutional ethics approval was required for this case report
Patient Consent: Obtained
ChatGPT (OpenAI) was used to assist in refining the language and clarity of the manuscript. All content was reviewed and edited by the authors, who take full responsibility for the accuracy and integrity of the final text.
