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Clinical presentation

Between 2003 and 2010, 111 adult patients with unilateral thalamic tumors underwent
surgical resection at our hospital. This group included 71 males and 40 females (ratio:
1.8:1). In 51/111 patients (45.9 %), the tumor was on the left side. The mean age
at presentation was 33.4?±?13.2 years (range, 18–64 years) and the mean duration of
symptoms was 3.6?±?6.4 months (range, 0.25–19 months). For 28/111 patients (25 %),
the tumor was present for less than 1 month prior to diagnosis, for 55/111 patients
(50 %) the tumor was present for 1–2 months prior to diagnosis, and for 28/111 patients
(25 %) the tumor was present for more than 2 months prior to diagnosis. The symptoms
reported for the present cohort are listed in Table 1. The most common presentation was increased intracranial pressure (ICP) (72/111,
65 %), which was characterized by headaches, vomiting, and papilledema. Motor deficits
were also a common presentation (44/111, 40 %).

Table 1. Clinical features for 111 adults with unilateral thalamic tumors

All patients underwent MRI before surgery. Special attention was given to the volume
and location of each tumor. The mean tumor volume was 38.4?±?28.9 cm 3] (range, 4–140 cm 3]). Tumors were also divided into two major groups based on their location in the MR
images. Tumors with an epicenter in the thalamic region were in one group, while tumors
arising from the junction of the thalamus and cerebral peduncle—with most of their
mass being in the thalamic region—were included in the second group. In the first
group (?=?84), the tumor epicenter was located in the anterior thalamic nuclei (?=?20), the lateral nuclei (?=?7), the medial nuclei (?=?18), or the pulvinar (?=?39). In this group, the tumors also extended in the anterior or superior direction
towards the front horn of the lateral ventricle (?=?14), medially toward the third ventricle (?=?11), laterally toward the adjacent lobe or gyrus (?=?7), and posteriorly toward the parietal and temporal lobes (?=?29). In the second group (?=?27), the tumors originated from the thalamus and extended to the midbrain.

Tumor resection

According to the location of each tumor on the preoperative MR images, several surgical
approaches were used. In cases where the epicenter was located in the anterior thalamus
with/without anterior extension to the fontal horn of the lateral ventricle or callosum,
the anterior transcallosal approach was used, provided that the tumor extended toward
the lateral ventricle without causing injury to the hemisphere tissue or cortical
incision. In cases where the tumor extended too far laterally, a transfrontal approach
was used to reach the frontal horn of the lateral ventricle, then the ventricle floor
was incised and the tumor was exposed. A transcallosal approach was used in 13 cases
(12 %), while a transfrontal approach was used in 7 cases (6 %) (Fig. 1). In cases where the tumor epicenter was located in the medial thalamic region with
or without extension into the third ventricle, the transcallosal approach was used
(17, 15 %) (Fig. 2). A stereotactic biopsy was performed in a single case (0.9 %). In cases where the
tumor epicenter was located in the lateral thalamic region with/without lateral extension
to the basal ganglia, adjacent lobes, or gyrus, and when the tumor extended beneath
the temporal cortex, the trans-temporal middle gyrus approach was used. The transtemporal
approach was used in 7 cases (6 %) (Fig. 3). For tumors located in the pulvinar with posterior extension toward adjacent structures,
a transparieto-occipital transventricular approach was used. For this approach, the
cortex was incised from the border of the parieto-occipital lobes and the sulcus was
dissected to reduce cortical injury and reduce the risk of postoperative seizures
and hemianopsia. The transparieto-occipital approach was used in 37 cases (33 %) and
stereotactic biopsy was performed in two (Fig. 4).

Fig. 1. a Different surgical approaches to anterior thalamic tumors were showed in the diagram.
b An anaplastic astrocytoma arising from anterior thalamus was resected totally via
an anterior transcallosal approach. c Another anaplastic astrocytoma was resected totally via a transfrontal approach

Fig. 2. a Different surgical approaches to medial thalamic tumors were showed in the diagram.
b An anaplastic astrocytoma was resected totally via an anterior transcallosal approach.
The tumor extends medially to the third ventricle, as seen on the preoperative MR
image. The top of the tumor is exposed after an incision into the callosum

Fig. 3. a Different surgical approaches to lateral thalamic tumors were showed in the diagram.
b The anaplasia astrocytoma arose from the lateral part of the thalamus and was removed
by transtemproal approach subtotally

Fig. 4. a Different surgical approaches to thalamic tumors arising from pulvinar were showed
in the diagram. b A glioblastoma arose from the posterior part of the thalamus and extended posteriorly
to the lateral ventricle, and was removed totally via a transparieto-occipital approach.
The cortex was incised with the help of neuronavigation

For tumors arising from the junction of the thalamus and cerebral peduncle with most
of their mass located in the thalamic region, the transparieto-occipital approach
was used to remove the thalamic part of the tumor. The inferior part that slightly
extended to the cerebral peduncle was also exposed and removed. If the tumor occupied
the cisterna ambiens and extended inferiorly to the infratentorial area, the tumor
could be exposed by elevating the temporal lobe and making a tentorial incision via
a subtemporal approach. If the tumor extended to the thalamic and peduncle to a similar
extent, the transtemporal approach was a good choice for both regions. Overall, the
transparieto-occipital approach was used in 16 cases (14 %), the transtemporal approach
was used in 2 cases (2 %), the subtemporal approach was used in 6 cases (6 %) (Fig. 5), and a stereotactic biopsy was performed in 3 cases (3 %).

Fig. 5. a Different surgical approaches to thalamic tumors arising from junction of pulvinar
thalamus and cerebral peduncle were showed in the diagram. b An astrocytoma was removed subtotally via a transtemporal approach. The tumor arose
from the junction of thalamus and cerebral peduncle and extended to both sides equally,
and both parts were well exposed via the transtemporal approach. c The inferior part of another astrocytoma was well exposed and removed via a subtemporal
approach. The postoperative MR image shows that some residual tumor was still present
in the thalamic region

Based on both the surgical findings and post-operative MRI findings, complete tumor
resection was achieved in 29 cases (26.1 %), subtotal resection was achieved in 54
cases (48.6 %), and partial resection was achieved in 21 cases (18.9 %). In Table 2, data regarding tumor location and the extent of resection are summarized. Taken
together, these results indicate that it was difficult to achieve total and subtotal
resection when tumor infiltration reached the midbrain.

Table 2. Extent of resection based on the anatomic location of the 111 adult unilateral thalamic
tumors

Perioperative morbidity and mortality

Five patients died during the perioperative period, two as a result of coma and three
as a result of cerebral swelling and infarction. Table 3 summarizes the postoperative clinical features of the other 106 patients upon discharge.
For sensory function, visual ability, and ICP, 80/106 cases (84.9 %), 100/106 cases
(94.4 %), and 100/106 cases (94.4 %) showed no decrease or improvement in these functional
categories, respectively. Regarding motor deficits, only patients with preoperative
motor deficits (?=?44) could be evaluated for improvement in motor deficits, yet all 106 patients
could be evaluated for deterioration of motor deficits. Therefore, preoperative motor
deficits were found to improve following surgery in 15/44 cases, while motor deficits
deteriorated in 23/106 cases (Table 3). For the latter, myodynamic muscle strength was also found to slightly recover in
15 of these cases within 3 months. A significant functional decrease in patients with
deteriorated motor deficits was observed when the intra-operative electrophysiological
monitor was used (18 cases in non-electrophysiological stage vs. 5 cases in electrophysiological
stage). In addition, new sensory deficits were detected in 16 cases (13 cases in non-electrophysiological
stage vs. 3 cases in electrophysiological stage), while a significant increase in
ICP was found in 6 cases (these patients underwent cranial decompression), and hemianopia
developed in 6 cases. Other complications included speech disorders, memory disorders,
involuntary movements, spasticity, seizures, and behavioral problems, which were observed
individually or in combination in 16 cases.

Table 3. Postoperative clinical features of 106 adults with unilateral thalamic tumors

Perioperative hydrocephalus was encountered before and after surgical resection. In
42 cases where hydrocephalus was identified preoperatively, four patients underwent
ventriculo-peritoneal (VP) shunt placement surgery at another hospital for treatment
of severe ICP symptoms. In 28 of the remaining 38 cases, the hydrocephalus improved
without VP shunt placement after tumor resection. In the other 10 cases, the hydrocephalus
did not improve and eventually a VP shunt was required. After tumor resection, ventricle
enlargement was observed in six patients that did not exhibit preoperative hydrocephalus,
including five patients who required a VP shunt and one patient who underwent placement
of an external ventricular drain.

Histopathological findings, adjuvant treatment, and survival analysis

Histopathology confirmed the following tumor types in the present series: 88 astrocytomas,
5 oligodendrogliomas, 12 oligoastrocytomas, 3 ependymomas, 2 gangliogliomas, and 1
primary neuroectodermal tumor (Table 4). Of these tumors, 50 were high-grade and 61 were low-grade. All patients with high-grade
tumors or progressive low-grade tumors completed postoperative radiotherapy and/or
chemotherapy, except for five patients who died during the perioperative period. In
addition, 20 patients were lost to follow-up. Of the remaining 86 patients, 40 had
high-grade tumors and 44 had low-grade tumors.

Table 4. Histological classification of adult unilateral thalamic gliomas of the present cohort
(?=?111)

Only 18 patients were alive at the time of the last follow-up (mean follow-up duration,
37.3 months; range, 6–98 months). The median survival times for patients with low-
and high-grade tumors were 40 and 12 months, respectively. The 1- and 3-year survival
rates of patients with low-grade tumors were 94.7 %?±?3.6 % and 57.7 %?±?8.1 %, respectively,
which were higher than those of patients with high-grade tumors (43.2 %?±?7.5 % and
6.8 %?±?3.8 %, respectively; P??0.001). The median survival period was longer for patients who underwent total
or subtotal resection compared with those who only underwent partial resection or
biopsy (28 vs. 12 months, respectively). The median survival period of patients with
high-grade tumors who underwent total/subtotal resection was 5.5 months longer than
for patients who only underwent partial resection or biopsy and adjuvant therapy (14.5
vs. 9 months, respectively). The median survival period of patients with low-grade
tumors who underwent total/subtotal resection was 12 months longer than for patients
who only underwent partial resection or biopsy (12 vs. 30 months, respectively) (Table 5). Compared with previously published series, the survival rate of the present series
of adult thalamic tumor patients was lower than that of pediatric patients with either
high-grade or low-grade tumors, yet was higher than that reported by Kelly et al.
for an adult cohort with high-grade tumors (Table 6). However, the number of poor outcomes indicate that thalamic tumors in adults need
to be further studied.

Table 5. Comparison of the present series with other published series of thalamic tumors

Table 6. The indications and complications of different surgical approaches to thalamic tumors

Multivariate Cox regression analysis was performed to identify variables that independently
affected survival (e.g., extent of tumor resection, tumor volume, age, duration of
symptoms, preoperative KPS score, histological findings). The results showed that
the extent of tumor resection (total/subtotal resection compared with partial resection/biopsy,
p?=?0.005), preoperative KPS score (KPS score???70 compared with??70, p?=?0.003) and histological results (high-grade vs. low-grade tumors, p?=?0.01) were correlated with patient survival.