In this study, the overall rate of complications due to EB and/or ETV was 5% (5 patients), which is consistent with previous reports, indicating the safety of EB and/or ETV [4, 22, 23, 28]. However, intratumoral hemorrhage was observed in two patients; both of these patients were in the ETV-alone group and were diagnosed with AT/RT. There was no other tumors developed intratumoral hemorrhage after ETV. To our knowledge, this is the first report to demonstrate the risk of intratumoral hemorrhage due to AT/RT after ETV for obstructive hydrocephalus. Considering that ETV did not directly damage the tumors, AT/RTs may themselves pose a high risk for intratumoral hemorrhage.
Efficacy of ETV as CSF flow diversion followed by tumor resection
Several authors have reported that the CSF flow-diverting procedure through EVD or shunt surgery for hydrocephalus makes the subsequent tumor excision more difficult and hazardous [11, 36]. Ideally, performing emergency surgery for hydrocephalus and tumor removal at the same time would be better. However, in the clinical setting, performing early tumor removal via craniotomy may not be possible. For such cases, performing CSF flow-diverting surgery before craniotomy would be a better choice. Furthermore, treating hydrocephalus by ETV could improve the general condition of patients. Corticosteroid therapy, EVD, and VPS placement have been performed as useful treatments for intracranial hypertension [27, 29]. Although corticosteroids may help reduce the posterior fossa swelling, EVD is required, and there remain severe risks due to the increased ICP, such as deterioration in the level of consciousness or visual affection due to papilledema [6]. EVD is commonly used to control ICP for obstructive hydrocephalus, but in the case of pediatric patients, maintaining them in the supine position is often difficult, which may cause difficulty in management until surgery. Precraniotomy VPS placement has several problems, such as upward herniation, infection, shunt malfunction, and abdominal complication [2, 8, 9, 15, 25]. Therefore, there have been increasing reports on the efficacy of ETV performed as preoperative CSF flow diversion followed by tumor resection [5, 10, 32, 34, 35].
Intratumoral hemorrhage due to preoperative CSF flow diversion followed by tumor resection
There are few reports on intratumoral hemorrhage after EVD, and the actual frequency remains unknown. To the best of our knowledge, the literature reports three cases of medulloblastoma, one case of germ cell tumor, and one case of astrocytoma [7, 13, 33, 36].
On the other hand, El-Gaidi MA et al. reported that 1 (1.1%) of 87 patients and 4 (1.9%) of 214 patients developed intratumoral hemorrhage of posterior fossa tumors after ETV and VPS placement, respectively [6]. Two patients died before tumor resection, and no information on pathology was available. One patient who underwent ETV was a 1.5-year-old boy in whom the subsequent craniotomy revealed astrocytoma. Two patients who underwent VPS placement were a 10-month-old boy and an 8-year-old girl in whom the subsequent craniotomy revealed ependymoma and medulloblastoma, respectively [6].
Kasilwal MK et al. also reported a case of a patient with postoperative (VPS) intratumoral hemorrhage who had hydrocephalus with a basal ganglionic tumor [16]. The cause of the intratumoral hemorrhage was described as a sudden decrease in ICP due to ventricular tapping, resulting in the disturbance of the dynamic balance between the various intracranial contents and causing an increase in cerebral blood flow and vascular congestion [16]. Moreover, the immaturity, fragility, and structural abnormality of tumor vessels were reported as causes of the hemorrhage [6]. In other words, intracranial hemorrhage is induced when the changes in ICP act on vulnerable blood vessels in the tumor.
In the present study, we detected intratumoral hemorrhage only in patients with AT/RT. Hence, AT/RT-specific properties were believed to be the cause.
AT/RT
AT/RTs are rare malignant intracranial tumors, representing only 1.3% of primary central nervous system (CNS) tumors in the pediatric population and 6.7% of CNS tumors in children younger than 2 years of age. These tumors have been categorized into grade 4 of the WHO classification of nervous system tumors published in 2000 [17, 30]. Loss of INI-1 expression is a characteristic feature of AT/RTs.5 Loss of BRG-1, the product of SMACA4 gene, is rarely observed in patients with AT/RTs [12]. According to the WHO classification of nervous system tumors published in 2016, the diagnosis of AT/RTs requires confirmation of such characteristic molecular defects [21].
Regarding the imaging characteristics of AT/RTs, studies have reported heterogeneity of lesions, intratumoral hemorrhage, hyperintensity on DWI, lower ADC values, presence of a tumor with off-midline location, and peripheral cystic components [14, 15, 18, 26, 37]. Chan et al. reported that the areas of hemorrhage suggest a vascular tumor, and AT/RTs are hypervascular tumors [3]. Hypervascular tumors have been demonstrated to have massive hemorrhage, and gross total resection is sometimes difficult [24]. A study reported a case of partial resection due to difficulty in reaching the edge of the tumor within the left lateral ventricle and the vascular nature of the tumor, which later developed an uncontrollable postoperative hemorrhage [3]. We preoperatively diagnosed two patients with AT/RT based on brain MRI findings. As the tumors were expected to be easily hemorrhagic, we decided to perform craniotomy at a later date and performed ETV alone for the treatment of hydrocephalus. During the procedure, extreme caution was taken to avoid touching the tumor. Unfortunately, intratumoral hemorrhage postoperatively developed.
Comparison between AT/RTs and medulloblastomas
There are some previous reports of medulloblastoma or glioma with intratumoral hemorrhage after ETV, but there are no reports of AT/RTs [6]. The majority of AT/RTs exhibit a complex histological pattern, such as choroid plexus carcinoma, germ cell tumor, ependymoma, glioblastoma, or embryonal tumor [1]. Before 2016, positive staining of rhabdoid cells with antibodies to epithelial membrane antigen was used to distinguish AT/RTs from other embryonal tumors [31]. Therefore, patients with AT/RTs may have been included in the category of those with postoperative intratumoral hemorrhage diagnosed with medulloblastoma or high-grade glioma among infant patients in previous reports. In the present study, INI-1 expression was confirmed in all the previous cases of medulloblastoma to clearly distinguish them from those with AT/RTs. Table 3 shows the results of comparison between these cases. The longer duration of operation was influenced by the longer duration until endoscopic introduction in the AT/RT group because of the patients being infants. Although the number of patients was small because of the rarity of the tumor, the incidence of intratumoral hemorrhage after ETV was higher in patients with AT/RTs than in those with medulloblastomas. As there were no patients with intratumoral hemorrhage among patients with any other malignant tumors, we would like to emphasize that ETV for AT/RTs is associated with a higher risk for intratumoral hemorrhage than that for other tumors.
Preventing intratumoral hemorrhage
To summarize, intratumoral hemorrhage may be caused by a sudden decrease in ICP, and it is more likely to be observed in cases of AT/RTs than in cases of other brain tumors.
In endoscopic procedures, ICP decreases to the same level as that of atmospheric pressure when sheath is inserted, which may pose a risk of developing intratumoral hemorrhage [38]. In contrast, in EVD, a sudden decrease in ICP could be prevented by taking precaution during ventricular tapping. Moreover, the one-way ball valve (Acty valve II, Kaneka Medix, Japan) set at high pressure can release pediatric patients from constraint during ventricular drainage [20]. Therefore, in patients with suspected AT/RTs in preoperative examination, EVD at high pressure may be preferable for ICP control.
Limitation
There were very few patients with AT/RTs to be statistically examined. We were unable to examine INI-1 expression before 2010 in tumors other than embryonal tumors. Moreover, previous studies have demonstrated intratumoral hemorrhage in not only medulloblastomas but also other high-grade gliomas. The difference between the findings of the present study and those of previous research is unclear because of the lack of detailed description. However, to our knowledge, this is the first report to describe the risk of hemorrhage due to ETV in patients with AT/RTs.