Intracranial schwannoma accounts for between 5 and 8% of intracranial tumors, whereas intracerebral schwannoma, a rare disease, accounts for <1% of intracranial schwannoma. A total of 84 cases previously reported within China and elsewhere were reviewed and summarized (Table I) (1–56). Gibson et al (5) reported a case of a 6-year-old male with a schwannoma in the temporal lobe that was surgically resected successfully for the first time in 1966. Erongun et al (33) summarized 35 cases (including the 1996 case), the youngest patient was 4 years old, whereas the oldest patient was 63 years old, with a median age of 21 years; the number of males and females was 18 and 17, respectively. Furthermore, brain schwannomas were predominantly identified in children and young people, including 26 patients <30 years old, accounting for 74.3% of total cases. Andrade et al (37) summarized and analyzed 55 cases reported in 2002, including 31 males and 24 females; the proportion of men was slightly higher at a male/female ratio of 1.29:1. Additionally, the median age was 21 years, and the age demonstrated a bimodal distribution, with 40 cases <30 years, accounting for 72.7% of total cases. The median age of the 36 cases with supratentorial tumors was 18 years, with a male/female ratio of 1.31:1, whereas the median age of patients with subtentorial tumors was 45 years, with a male/female ratio of 1.25:1. Patients with supratentorial intracerebral schwannomas were typically younger, whereas patients with subtentorial intracerebral schwannomas were older; however, no significant difference was identified between the incidence in men and women irrespective of supratentorial or subtentorial intracerebral schwannoma. A total of 84 cases reported within China and elsewhere were reviewed and analyzed, including 47 males and 37 females with a male/female ratio of 1.27:1. Furthermore, the youngest case was 6 months old, whereas the oldest case was 84 years old, with a median age of 23 years. Notably, the age demonstrated a bimodal distribution, including 55 cases <30 years, accounting for 65.5% of total cases. Additionally, the median age of the 61 cases with supratentorial intracerebral schwannomas was 21 years; however, the median age of patients with subtentorial intracerebral schwannomas was 48 years (Fig. 5). Therefore, this suggests that intracerebral schwannoma occurred at no specific age and demonstrated bimodality, with a peak at ~20 years; however, the age of the majority of patients was <30 years. Furthermore, the proportion of males was higher compared with females, which is consistent with the characteristics of intracranial tumors. Additionally, the incidence of supratentorial intracerebral schwannoma was increased at a younger age (median of 21 years), whereas the incidence of subtentorial intracerebral schwannoma was increased at an older age (median of 48 years). However, the present case report describes a 12-year-old female who was diagnosed with a subtentorial schwannoma in the brainstem. To the best of our knowledge, this present case report is the second to diagnose the disease in a patient ≤12 years of age.

The majority of intracerebral schwannomas are supratentorial, which typically occur in the superficial sections of the brain parenchyma or near the ventricle; however, previous studies have demonstrated that these are likely to occur in the frontal and temporal lobes of the cerebral hemisphere, as well as within the cerebellar hemisphere, cerebellar vermis and the fourth ventricle (4,39). Erongun et al (33) summarized that 27/35 cases (77.1%) with supratentorial intracerebral schwannomas occurred at a younger age with a distribution of 9 cases in the frontal lobe, 5 cases in the parietal lobe, 5 cases in the temporal lobe, 3 cases in the top occipital lobe, 1 case in the frontotemporal lobe and 1 case in the cerebral hemisphere. Andrade et al (37) demonstrated that 36/55 cases (65.45%) had supratentorial intracerebral schwannomas, including 13 cases in the frontal lobe, 12 cases in the temporal lobe, 9 cases in the parietal lobe, 1 case in the occipital lobe and 1 case in the cerebral hemisphere. Furthermore, of the 19 cases with subtentorial intracerebral schwannomas, 6 were located in the brainstem, and 13 were in the cerebellar hemisphere and vermis. In addition, Consales et al (50) provided further evidence for the distribution of intracerebral schwannoma and summarized 12 cases in 2010, including 3 cases in the frontal lobe, 4 cases in the temporal lobe, 1 case in the parietal lobe, 2 cases in the cerebellum, 1 case in the brainstem and 1 case in the hypothalamus. In total, 84 cases (Fig. 6) were summarized, including 61 cases of supratentorial intracerebral schwannomas (72.6%), of which 24 were in the frontal lobe, 17 were in the temporal lobe, 12 were in the parietal lobe, 6 were in the occipital lobe and 2 were in the hypothalamus. Furthermore, 15 cases with subtentorial intracerebral schwannomas were in the cerebellar hemisphere and 8 cases were in the brainstem. Therefore, it can be concluded that intracerebral schwannomas are primarily supratentorial, typically located in the frontotemporal lobe, whereas subtentorial intracerebral schwannoma accounts for <33% of the total intracerebral schwannomas, of which schwannomas within the brainstem exhibit an increased incidence. It is inferred that this part is close to the cranial nerves of the brainstem, which may be associated with the origin of intracerebral schwannoma.

Intracerebral schwannoma has no specific clinical manifestation, and it is not classified by age. Its main clinical manifestations include epilepsy, increased intracranial pressure and local neurological dysfunction. Clinical manifestations in 84 patients were summarized and analyzed. The primary manifestations for patients <25 years old were headaches and epilepsy; however, elderly patients primarily suffered from acute local neurological dysfunction.

Results obtaining from imaging analysis demonstrated that characteristics of intracerebral schwannomas were similar to those of normal intracranial schwannomas. A typical imaging feature (57) of intracranial schwannomas was cystic masses with a clear boundary. Tumors were primarily located in the superficial part of the brain parenchyma, or the brain parenchyma near the ventricle with calcification. Additionally, edema was observed in the surrounding brain tissue, and the solid part of the tumor was homogeneously enhanced. However, not all intracranial schwannomas presented with cystic degeneration. It has been previously reported that 25.7% of tumors presented with cystic degeneration; however, calcification was rare (33). Results obtained from imaging analysis of the 12-year-old female included cystic mass lesions in the brainstem parenchyma, in which MRI T1 sequence and MRI T2 sequence mixed signal solid signal shadows were observed on the posterior capsule wall, and long T1 and short T2 signal shadows were observed in the tumor parenchyma. A combination of the aforementioned imaging results with high-density head computer tomography results demonstrated calcified shadow, deformation of the brainstem and cerebellar tissues around the tumor due to compression and mild edema. Parenchyma was strengthened following enhancement. Thus, no significant difference was reported between intracerebral schwannoma and ordinary schwannoma in MRI; however, there was a difference in the pathogenic site of origin (57).

The origin of the intracerebral nerve sheath remains unclear. It is well-documented that Schwann cells do not exist in the brain parenchyma; they are primarily in the choroidal tissues of the subarachnoid space, and the intracranial peripheral vascular plexus of the ventricle. Certain researchers believe that specific soft membrane cells have the potential to transform into Schwann cells, which are the origin of intracerebral schwannomas (58). Although the development of intracerebral schwannomas remains unclear, the majority of researchers claim that intracerebral schwannomas originate from the subarachnoid space and peripheral venous plexus (59). Nerve fibers of the trigeminal nerve that dominate the dura mater are considered to be the origin of intracerebral schwannomas near to the dural convexity; however, certain intracerebral schwannomas are located deep in the brain parenchyma and peripheral vascular plexus of the cerebral arteries. This is because the majority of intracerebral schwannomas are located in superficial sections of the brain surface or near the ventricle adjacent to the brain surface. Therefore, Schwann cells in the peripheral venous plexus of the subarachnoid space may proliferate inward and further transform into intracerebral schwannomas (60,61). Several previous studies have investigated molecular markers and confirmed that Schwann cells originate from neural crest cells. SRY-related HMG-box 10 (SOX10) exists throughout the maturation process, activator protein 2α (AP2α) exists in the precursor stage prior to neural crests transforming into Schwann cells and cadherin-19 exists only in the precursor stage of Schwann cells. Brain fatty acid-binding protein and P0 markers exist in the precursor stage and later stages of Schwann cell maturation. GFAP and S-100 are expressed in the immature stage of Schwann cells but not in Schwann cell precursors. Early developmental markers including paired box (PAX)3 and PAX7 are often associated with malignancy, whereas AP2α and markers of late SOX10 are present in relatively benign tumors including schwannomas and gangliomas. Notably, PAX3 and PAX7 are present in the mesoderm, whereas AP2α and SOX10 are expressed in the ectoderm. However, IHC staining of intracerebral schwannomas revealed S-100 (+), GFAP (−) and EMA (−). Neural crest cells directly differentiate into Schwann cell precursors that further transform into immature Schwann cells, which at the stage of fetal birth differentiate into medulla or demyelinated Schwann cells (60–63). Therefore, it has been suggested in previous studies that neural crest cells trapped in the brain at the stage of embryonic development are the cause of the occurrence of intracerebral schwannomas (64). Russel and Rubinstein (1) considered that mesenchymal cells with a soft membrane and Schwann cells exhibit tissue similarity, and the histological transformation may lead to schwannomas of the central nervous system.

Intracranial schwannoma accounts for ~8% of intracranial tumors and is not age-specific; however, previous results suggest a peak incidence at an age between 40 and 60 years, without sex orientation in the incidence rate. However, intracerebral schwannoma is a rare disease and accounts for <1% of intracranial schwannomas. In addition, the number of males is greater compared with the number of females, which may be due to the fact that, overall, more male patients are diagnosed with intracranial tumors compared with females. Typical schwannomas have two types of tissue conformations: The dense Antoni A and the loose Antoni B (65). Histopathological analysis of the 12-year-old case revealed a staggered arrangement of sparse and dense areas of the Schwann cell, which was associated with local focal calcification. Tumor cells were oval with small nuclei; however, the mitotic figure was difficult to observe. IHC staining demonstrated that S-100 was expressed in tumor cells, negative expression of EMA and GFAP was able to distinguish meningiomas and gliomas, and the proliferation index of Ki-67 was not increased (1% of positive expression) indicating that tumor cell proliferation was slow.

The prognosis for the majority of cases reviewed in the present case report was classified as being good; however, 3 cases (23,33,42) demonstrated a markedly high level of malignancy (spread to other organs) and Rodriguez et al (23) reported 1 case of moderate malignancy (intracranial relapse), and, despite reoccurrence of the tumor, the prognosis was good following a second round of surgery. Bruner (24) reported a patient who succumbed 5 months after surgery due to postoperative secondary meningitis. Erongun et al (33) reported a 4-year-old female who presented with a tumor in the left parietal lobe and a high level of malignancy, as demonstrated using postoperative pathological analysis. Furthermore, the patient received surgery three times within an 8-month period and died from complications generated from having multiple surgeries 1 month after the last operation. The 5-year follow-up on the 12-year-old female revealed no reoccurrence of the tumor and also the neurological dysfunction of the patient had improved.