4.1 Intracranial Teratoma

Teratoma is the most prevalent germ cell tumor and accounts for the majority of prenatally diagnosed brain tumors [13]. Although many cerebral teratomas used to be identified only during postmortem examinations, they are now more frequently detected through routine prenatal US at around GA 27 weeks [14]. Fetal MRI can further characterize the morphology and accurately describe the lesion extent in more detail. Fetal intracranial teratomas can differ substantially in both size and weight [15] and usually have a more aggressive MRI presentation than postnatal teratomas. These teratomas often present as heterogeneous masses that vary in size and, in some cases, occupy a substantial portion of the intracranial region. They often contain cystic, solid, and calcified elements [16]. Although intralesional fat is a characteristic feature of teratomas, it is often difficult to detect through prenatal imaging.

Cassart et al. [3] demonstrated that MRI has a higher sensitivity than US for detecting teratoma heterogeneity because of its superior contrast resolution, which can identify the presence of tissue from all three germ cell layers within these tumors. Furthermore, teratomas commonly have cysts and may sometimes be entirely cystic and correspond to necrotic lesions. These types of cysts are uncommon in other tumor types.

In addition to cysts, the heterogeneous appearance of this tumor may also result from hemorrhagic components. These components are readily identified on T1 and T2* sequences, although extensive intraparenchymal hemorrhage can complicate their differential diagnosis. Because hematomas have different sizes, shapes, and signals in a short period from the first examination, whereas teratomas may not, a follow-up examination is usually required to obtain additional findings [17]. Nonetheless, prenatal MRI is capable of accurately characterizing teratomas as well as several other types of fetal intracranial tumors.

Because teratomas can often be large lesions, US is often not the best option for assessing tumor extension. MRI offers a superior evaluation of tumor extension thanks to its wider field of view and enhanced contrast resolution [18]. The accurate assessment of the extent of the tumor and its impact on surrounding structures is essential for assessing prognosis, determining the feasibility of surgical resection, and evaluating potential postoperative outcomes. The size of the tumor may have a greater effect on prognosis than its histological nature. Large or rapidly growing tumors are frequently associated with poorer outcomes, whereas tumors < 3 cm that are detected in late pregnancy tend to have more favorable postpartum prognoses.

4.2 Astrocytoma

Astrocytoma is the primary type of glial tumor. The most common fetal astrocytoma is glioblastoma multiforme; however, other forms, such as low-grade or anaplastic astrocytoma and desmoplastic infantile astrocytoma, can also occur [19]. In both fetal and postnatal MRI, congenital glioblastoma multiforme tumors typically appear isointense or slightly hyperintense to the brain on T1-weighted images and isointense on T2-weighted images. These tumors may also show signs of hemorrhage and necrosis [20]. The prenatal diagnosis of congenital intracranial astrocytomas, and especially anaplastic astrocytomas, has received limited attention until recently. Although fetuses with anaplastic astrocytoma tend to have a better prognosis compared to those with other congenital intracranial tumors, the imaging characteristics of these tumors often overlap, and a definitive diagnosis relies on pathological examination.

Fetal astrocytomas typically appear as large ventricular masses resulting in midline structure displacement, obstructive hydrocephalus, and prominent cranial deformities [21]. As illustrated by Huang et al. [20] and other clinical observations, congenital anaplastic astrocytoma with intratumoral hemorrhage generally appears as a low signal on T1-weighted images and exhibits heterogeneous isointensity or a high signal on T2-weighted images. Fetal MRI may also be helpful for determining the exact localization of the remaining brain structures and tumors.

The reported GA at diagnosis before delivery varies from 31 to 42 weeks (mean 35.9 weeks), which is later than that for other congenital brain tumors. However, these tumors can proliferate quickly. Survival rates vary, from 20% for high-grade lesions to 90% for low-grade lesions, with an overall average survival rate of 46%. Huang et al. therefore proposed that cesarean delivery should be performed if anaplastic astrocytoma is detected prenatally [20]. This is particularly important, and postpartum interventions should be considered.

4.3 Craniopharyngioma

Craniopharyngiomas are primarily diagnosed in children within the first 2 decades of life, representing 8%–10% of all intracranial tumors in this age range [22, 23]. Although craniopharyngioma is rarely detected during the fetal period, the use of advanced, noninvasive diagnostic techniques such as US and MRI means that an increasing number of cases are being identified in utero. Fetal MRI is particularly crucial because it aids in determining the optimal timing for a safe pregnancy termination [24]. Moreover, based on the morphological features and location of a tumor, clinicians can predict its possible histopathological characteristics. Craniopharyngiomas are challenging to differentiate from other solid suprasellar masses, including tumors (such as teratomas, astrocytomas, and hamartomas) or malformations (including hypothalamic malformations), because they often present with similar imaging characteristics [9].

4.4 Choroid Plexus Tumor

Choroid plexus tumors (CPTs) are neuroectodermal papillary growths that arise from the epithelium of the ventricular choroid plexus [25]. Although CPTs are rare, they represent 42% of cerebral tumors in neonates [26], and patient prognosis varies substantially depending on histological classification. CPPs are more common than choroid plexus carcinomas (CPCs), and lower-grade tumors are more frequent than higher-grade tumors. CPTs typically present with rapid perinatal hydrocephalus, which is a key indicator that should prompt clinicians to perform neuroimaging [4].

Prenatal examinations at GA 18–20 and 27–31 weeks are particularly important to screen for fetal central nervous system disorders [27]. Fetal MRI is probably the most useful of the radiological procedures that can provide high-quality images for surgery. In particular, MRI provides more accurate morphology during the early stages of gestation, allowing for early diagnosis, surgical planning, and treatment initiation. Another advantage of MRI for distinguishing among the different types of CPTs is the ability to use specialized techniques. MRI in prenatal diagnosis also serves to differentiate intracranial tumors from hematomas as early as mid-gestation and to detect regions of necrosis [28]. Magnetic resonance spectroscopy (MRS) can identify a lack of creatine and the neuronal/axonal marker N-acetylaspartate, thereby aiding in the distinction between CPPs and CPCs. Choline and lactate levels are reportedly higher in CPCs than in CPPs, whereas inositol levels are significantly higher in CPPs [29].

4.5 Medulloblastoma

Congenital medulloblastoma is an exceptionally rare brain tumor in children, accounting for 15%–20% of all cases [29]. To our knowledge, only one case has been reported in which this kind of tumor was identified antenatally through MRI. Korostyshevskaya et al. [11] reported a rare MRI finding of fetal medulloblastoma, accompanied by postnatal follow-up and treatment. During GA Week 31, a pregnant woman underwent routine fetal MRI that revealed a midline cerebellar lesion measuring ≤ 2 cm in size with mild T2 low signal and T1-defined high signal. In addition, quantitative MRI was performed, including ADC and fast MPF mapping. The lesion exhibited notably reduced ADC and elevated MPF.

This case highlighted the effectiveness of the fast MPF mapping technique for characterizing fetal intracerebral lesions. Initially developed for the quantitative analysis of brain myelin formation, MPF mapping has recently been applied to evaluate the early stages of fetal myelin development [30, 31]. Elevated MPF in tumor tissue is most likely caused by collagen deposition, which is typical of connective tissue ameloblastomas. This condition is characterized by an overproduction of collagen-rich reticular fibers that occupy the extracellular space. The contrast of a tumor on MPF and ADC maps in the fetal brain may reflect its histopathological origins, particularly in relation to collagen content and cell density.

4.6 Ependymoma

Fetal ependymoma is rare and accounts for only 2%–3% of all congenital brain tumors. The first and only case of ependymoma associated with Down syndrome was discovered incidentally during an autopsy of a female fetus in a 42-year-old woman following the termination of a pregnancy in GA Week 19 [32]. Among the different ependymoma subtypes, the anaplastic form is the most common and is classified as a World Health Organization Grade III lesion. Most case reports describe mesenchymal ventricular meningiomas, which are characterized by their large size, supratentorial location, lobulated shape, and frequent calcifications. Additionally, the lesion may extend into the posterior cranial fossa. Fetal ependymomas are typically linked to a poor prognosis [33].

4.7 Atypical Teratoid/Rhabdoid Tumors

ATRTs are highly aggressive World Health Organization Type IV embryonal tumors and are predominantly diagnosed in children under the age of 3 years [34]. Imaging typically reveals these tumors as large, heterogeneous neural masses featuring a mix of solid, cystic, and necrotic areas distributed across different regions. Given their highly complex cytoarchitecture, the MRI features of ATRT are similar to those of medulloblastomas. The timely and accurate diagnosis of ATRT is crucial because aggressive and active treatment is necessary to alter its natural progression [35].

4.8 Tuberous Sclerosis

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder that occurs in approximately 1 in 6000 individuals [36]. Most cases occur de novo, and a TSC diagnosis is sometimes considered in the case of prenatal cardiac tumors (unique or multiple) [37]. The ability of fetal MRI to detect cardiac transverse myxoma and other key features, such as cortical nodules (dysplasia) or subventricular nodules, has led researchers [38] to conclude that fetal MRI is an ideal component of diagnostic testing in early fetuses with suspected TSC. Goergen et al. reported that, in fetuses with confirmed TSC who underwent MRI, the probability of abnormal cranial findings varied significantly with GA [39]. This study emphasizes the capability of fetal MRI to diagnose TSC in fetuses (GA ≤ 24 weeks) and stresses the importance of considering TSC when fetal hemimegalencephaly, macrocephaly, or tumor-like brain lesions are detected.

4.9 Other Tumor-Like Masses

Tumor-like masses, including subcortical heterotopias, arachnoid cysts, vein of Galen aneurysms (VGAM), periventricular leukomalacia, and subdural hemorrhage, must be considered in the differential diagnosis of congenital brain tumors. Giant subcortical heterotopia is a rare condition that is characterized by a mass-like nodular conglomerate of dysplastic gray matter, which can replace large areas of cerebral lobes or even entire hemispheres. MRS can be helpful for revealing the absence of spectral abnormalities, indicating a hamartomatous rather than neoplastic nature [40].

The prenatal diagnosis of VGAM is usually performed in the late stages of pregnancy [41]. In recent years, fetal MRI has been demonstrated to be superior to color Doppler US for the diagnosis of VGAM. The arterial blood supply and involved veins of VGAM are relatively easily observed on single-shot turbo spin-echo images (black blood sequence) [42]. The majority of prenatal intracranial hemorrhages originate in the germinal matrix (approximately 67%), followed by the cerebral or cerebellar parenchyma, choroid plexus, and subdural and subarachnoid spaces. In rare instances, severe intracranial hemorrhage during fetal development—often caused by hematologic disorders such as vitamin K deficiency—may resemble malignant hemorrhagic tumors (e.g., ATRTs) [43]. However, follow-up imaging typically reveals a substantial decrease in the size of a hemorrhagic lesion as a result of clot shrinkage.

4.10 Pregnancy Management Options

The main approach for treating perinatal brain tumors is surgery, often beginning with the placement of a shunt. In some cases, chemotherapy is administered thereafter. Surgery can also provide a histological specimen to allow for an accurate diagnosis.

4.11 Clinical Prospects and Future Directions

The diagnosis of fetal intracranial tumors currently relies heavily on classical MRI sequences such as T1- and T2-weighted imaging, which provide excellent anatomical resolution and are essential for initial lesion detection and characterization. In the cases presented in the current review, T2-weighted imaging was emphasized because of its ability to clearly delineate the anatomical features of lesions. However, new sequences such as diffusion-weighted imaging, susceptibility-weighted imaging, and MRS play a crucial supplementary role in refining the diagnostic process. For example, diffusion-weighted imaging offers insights into cellular density and diffusion restriction, susceptibility-weighted imaging is highly sensitive to hemorrhage and calcifications, and MRS provides metabolic information that can aid in tumor characterization. Nevertheless, it is important to acknowledge that these advanced sequences are not yet universally available or routinely applied in all clinical settings, which may limit their widespread adoption. Looking ahead, the integration of new sequences, including the sequences introduced in the present review, holds significant promise for improving diagnostic accuracy and prognostic assessment. Future research should focus on validating the clinical utility of these sequences as well as on exploring their potential for differentiating tumor types, predicting histological grades, and guiding treatment decisions. Furthermore, the combination of advanced imaging techniques with artificial intelligence-based analysis may revolutionize prenatal diagnostics by enabling automated lesion detection and characterization.