After admission, cranial CT examination showed a low-density round-like occupying lesion in the fourth ventricle, with surrounding calcification, compression of the aqueduct, symmetrical enlargement of the third ventricle and lateral ventricles, suggesting obstructive hydrocephalus (Figure 1). MRI examination showed a round-like cystic tumor measuring approximately 4.8 cm × 4.8 cm × 4.0 cm in the fourth ventricle (Figure 1). The cystic portion of the lesion showed slightly high signal in T1-weighted image and obvious high signal in T2-weighted image. The cystic portion of the lesion was slightly high signal in T1-weighted image, and it was obviously high signal in T2-weighted image, and there was no obvious enhancement in the enhanced scan, and the fourth ventricle was narrowed and fissured by the compression. There was no extension of the lesion to the saddle region or suprasellar region, and the anatomy of the pituitary stalk, pituitary proper and optic cross was clear with normal signal (Figure 1). There was no intracranial multifocal lesion, and no supratentorial area occupation was seen. Combined with the imaging manifestations, cystic tumor of the fourth ventricle was initially considered, and further differential diagnosis was needed. Preoperatively, we mainly considered ventricular meningioma, intraventricular epidermoid cyst or atypical glioma and ectopic craniopharyngioma.

The patient was placed in the prone position under general anesthesia, and a median suboccipital craniotomy was performed. Under the microscope, the fourth ventricle was entered through the cerebellar hiatus, and the tumor was revealed after opening the cerebellar plexus. The lesion was located in the cavity of the fourth ventricle, and the cystic part was obviously tense. Firstly, we punctured and aspirated the “brown greasy fluid”, and the shiny crystals could be seen under the microscope. The cystic wall was separated from the solid part and resected. The cystic wall tumor was gray, tough, and partially adhered to the tissue at the base of the fourth ventricle, with clear boundaries. On the basis of fully protecting the medulla oblongata and the conduit orifices, the entire lesion was gradually resected. No obvious hemorrhage or brainstem injury was observed during the operation. Postoperative CT and MRI showed that the tumor had been completely resected and the fourth ventricle was well reconstructed (Figure 2). After surgery, the patient awoke well, with no new neurological deficits, and his gait returned to normal. No hydrocephalus was found in the repeat cranial CT, and the external drain was removed on the 4th day after surgery.

Intraoperative samples were taken and sent for pathologic examination; microscopically, basal fenestrated arrangement of squamous cells with papillary growths, interstitial laxity, and abundant vascularity were seen. Abundant wet keratin deposition, focal calcification and cholesterol clefts were seen. Immunohistochemistry suggested CK-P (+) and strong nuclear positivity of β-catenin cells, which supported adamantinomatous type of craniopharyngioma (Figure 3). The Ki-67 proliferation index was about 10%, and there was no anisotropy or active mitosis.

The patients recovered well after surgery without complications such as low sodium or pituitary dysfunction. No tumor recurrence was seen in the 3-month postoperative review. The patient’s life status is good and her neurological function score is perfect, she has resumed her normal life and work.

Craniopharyngiomas typically originate in the sella turcica region, but although rare, ectopic occurrences have been documented in the literature. These ectopic craniopharyngiomas may be found in locations such as the clivus, nasopharynx, third ventricle, cerebellopontine angle, and fourth ventricle (9). Regarding the formation mechanism of primary craniopharyngiomas of the fourth ventricle, the commonly accepted hypothesis is the embryonic developmental abnormality theory, i.e., during upward migration of the Rathke’s capsule, some of the epithelial cells are “lost” and remain in the subcapsular region, which later evolve into tumors (7). The epithelial chemotaxis hypothesis has also been proposed, in which neuroepithelial cells undergo chemotaxis in response to certain stimuli to form squamous epithelium, which in turn becomes tumorigenic (2). However, the latter has limited evidence and has not been widely supported (8). In our case, there was no history of any tumor in the saddle region or previous neurosurgery, and MRI showed clear anatomy and normal signal in the saddle region and suprasellar region, with no tumor extension, which clearly supported the diagnosis of “primary isolated fourth ventricle craniopharyngioma” (6). This is highly consistent with the case reported by Ahmed et al. in 2023 (4).

Typical craniopharyngiomas are imaged as mixed cystic and solid, with cystic fluid often high signal on T1-weighted images and high signal on T2-weighted images, and foci of calcification are clearly visible on CT (10). However, in cases of ectopic fourth ventricle, the imaging features are often atypical. Most cases in the literature have shown solid or inhomogeneous enhancement, with less cystic degeneration, which can be easily misdiagnosed as ventricular meningioma, astrocytoma, and intraventricular cyst (11). In this case, the image showed a cystic lesion within the fourth ventricle, and the calcified foci were clearly visible on CT, with slightly high signal in T1 and obviously high signal in T2, and no obvious enhancement was seen in the enhancement scan, suggesting that the inner part of the lesion contained high-protein or lipid components, which was close to the typical performance of craniopharyngiomas in saddle region (12). However, due to its special location, craniopharyngioma was not listed as the first choice of diagnosis before surgery, suggesting that the sensitivity of ectopic lesions should be improved in clinical work (13).

The pathology of this case was adamantinomatous type of craniopharyngioma with features including nests of squamous epithelial cells, stellate reticulation, wet keratins, and cholesterol clefts, positive immunohistochemical nuclei for β-catenin, and a low Ki-67 index (14, 15). This subtype is common in children and adolescents, but is also seen in adults and accounts for the majority of reported fourth ventricle cases (16, 17). In contrast, the papillary type tends to be adult-onset, with predominantly solid enhancement on the image, often accompanied by the BRAF V600E mutation; however, the papillary subtype is not present in all current reports of fourth ventricles (18).

The choice of surgical route for posterior cranial fossa tumors is very critical, and the suboccipital median approach combined with the cerebellar pallidum approach is the current standard strategy for the management of tumors in the fourth ventricle, which can protect the brainstem and cerebellar functional areas while fully exposing the tumor (19). In this case, complete resection was successfully achieved intraoperatively, and the postoperative recovery was good, suggesting high surgical safety and feasibility. It has been reported in the literature that if the tumor can be completely resected, the prognosis is usually good; if it is incompletely resected, the risk of recurrence is significantly increased, and it is recommended to cooperate with fractionated stereotactic radiotherapy (FSRT) or Gamma Knife therapy in the postoperative period (20, 21). There is no clear consensus in the current literature recommending whether ectopic craniopharyngiomas should routinely receive radiotherapy, but recurrences are mostly associated with intraoperative residuals (22).

Modern craniopharyngioma management emphasizes multimodal therapy and individualized strategies. International guidelines, such as those from the European Association of Neurological Surgeons (EANS) (23), emphasize balancing long-term tumor control with preserving patient quality of life, particularly hypothalamic function. Surgical resection remains the primary initial treatment modality, with the choice between endoscopic transnasal approaches or craniotomy determined by tumor origin, subtype, and extent of extension. For tumors with significant adhesion to critical structures like the hypothalamus, current trends favor avoiding aggressive radical resection to reduce severe complication risks. Instead, a strategy of surgical debulking followed by postoperative radiotherapy is increasingly adopted. Additionally, targeted drug therapies (e.g., BRAF/MEK inhibitors) offer new hope for recurrent or refractory cases (24).

As of 2024, eight cases of primary fourth ventricular craniopharyngiomas have been definitively reported, all without saddle extension or surgical history, and with a predominantly adamantinomatous type of pathology (22). The present case may be the ninth in the literature. A review of the literature suggests that this type of lesion, although rare, is not incidental and should be considered as one of the differential diagnoses for occupying lesions in the posterior cranial fossa, especially when imaging suggests mixed cystic-solid structures, lipoid-containing components, or calcifications (25, 26).