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. 2020 Sep 15;44(4):1833–1852. doi: 10.1007/s10143-020-01357-5

Spinal intramedullary schwannomas—report of a case and extensive review of the literature

V M Swiatek 1, K-P Stein 1, H B Cukaz 1, A Rashidi 1, M Skalej 2, C Mawrin 3, I E Sandalcioglu 1, B Neyazi 1,✉
PMCID: PMC8338859  PMID: 32935226

Abstract

Intramedullary schwannomas (IMS) represent exceptional rare pathologies. They commonly present as solitary lesions; only five cases of multiple IMS have been described so far. Here, we report the sixth case of a woman with multiple IMS. Additionally, we performed the first complete systematic review of the literature for all cases reporting IMS. We performed a systematic review of the literature in PubMed, EMBASE and Cochrane Central Register of Controlled (CENTRAL) to retrieve all relevant studies and case reports on IMS. In a second step, we analysed all reported studies with respect to additional cases, which were not identified through the database search. Studies published in other languages than English were included. One hundred nineteen studies including 165 reported cases were included. In only five cases, the patients harboured more than one IMS. Gender ratio showed a ratio of nearly 3:2 (male:female); mean age of disease presentation was 40.2 years; 11 patients suffered from neurofibromatosis (NF) type 1 or 2 (6.6%). IMS are rare. Our first systematic review on this pathology revealed 166 cases, including the here reported case of multiple IMS. Our review offers a basis for further investigation on this disease.

Keywords: Schwannoma, Spinal tumour, Intramedullary tumour, Review of the literature

Introduction

Within the group of central nervous system tumours, spinal tumours represent a minor fraction of 15% of all cases [1]. Spinal schwannomas represent about 10% of all spinal tumours [1]. Schwannomas occur most frequently within the intradural-extramedullary compartment [1]. The intramedullary location of schwannomas is a rare condition (0.3–1.5%) [2–4]. Furthermore, they commonly present as solitary lesions. To date, only five cases of multiple intramedullary schwannomas (IMS) have been described [5–9].

Here, we report a 6th case of a female patient with histologically proven IMS of the cervical spinal cord and an additional small lumbar localized lesion. Additionally, we performed the first complete systematic review of the literature searching PubMed, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) for all cases reporting IMS.

Case report

A 53-year-old woman presented with a 4-month history of progressive sensory deficits of the upper and lower limbs, without any further neurological symptoms. There were no neurofibromatosis (NF) stigmas and no history of genetic disorders or spinal injury.

Clinical presentation

Neurological examination revealed hypaesthesia of the first three fingers of the right hand, the right lateral lower leg and the right lateral foot edge. There was no paresis of the upper and lower limbs; the muscular tension was normal. The muscle stretch reflexes were normal and symmetrical. No pyramidal tract signs were present, nor spinal ataxia. The patient was defined as grade I according to the modified McCormick scale [10, 11].

Imaging findings and additional diagnostics

Magnetic resonance imaging (MRI) of the neurocranium and the cervical spine revealed a 9.3 × 19 mm intramedullary lesion at the level of C2/3, which was isointense on T1-weighted and had both hypo- and hyperintense components on T2-weighted images. The lesion showed intense heterogenous contrast enhancement and caused a massive perilesional spinal cord edema extending from the medulla oblongata to the level of C6 (Fig. 1).

Fig. 1.

Fig. 1

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a–c Preoperative MRI of the cervical spine in sagittal (a, b) and transverse (c) slides. T2-weighted images show a hypo- and hyperintense intramedullary lesion at the level of C2/3 (a). T1-weighted images show a heterogeneous gadolinium-enhanced tumour in the sagittal (b) and transverse (c) slides. d–f Preoperative MRI of the lumbar spine in sagittal (d, e) and transverse (f) slides. T2-weighted images show a hypointense lesion at the level of L2/3 (d). T1-weighted images show a homogenous gadolinium-enhanced tumour in the sagittal (e) and transverse (f) slides. g–i Postoperative MRI of the cervical spine in sagittal (g, h) and transverse (i) slides confirming the complete tumour resection

Combining the MRI findings and the neurological examination, we considered a preliminary diagnosis of intramedullary ependymoma. As a consequence, further investigations including a holospinal MRI and a lumbar puncture were carried out to examine the possible presence of drop metastasis. The holospinal MRI revealed a second small (3.4 × 4 mm) lesion at the level of L2/3. The lesion was isointense on T1-weighted and hypointense in T2-weighted images with homogenous contrast enhancement (Fig. 1). Cerebrospinal fluid examination showed no evidence of atypical, potentially malignant cells.

Operative findings and histopathology

The patient underwent uneventful microsurgical tumour resection through a posterior cervical approach and midline myelotomy with subsequent C2–C3 laminoplasty. Intraoperatively, the tumour appeared as a solid, yellowish mass comparable with a schwannoma. Complete tumour resection was achieved via meticulous microsurgical technique and ultrasonic aspiration. Intraoperative monitoring (somatosensory-evoked potentials) remained stable during the entire surgical procedure.

Microscopic examination of tissue samples obtained during surgery showed spindle-shaped cells, arranged in a typical fascicular pattern. Small areas consisted of a hypocellular myxoid structure. Old haemorrhages were frequently seen. Immunohistochemistry revealed a strong homogenous reaction for S-100 protein but was negative for epithelial membrane antigen. The proliferation rate (Ki-67 staining) was low (Fig. 2). Altogether, these findings were consistent with a histopathological diagnosis of a schwannoma.

Fig. 2.

Fig. 2

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Predominantly spindle cell tumour with fascicular (*) and small myxoid (#) areas (a). Strong immunopositivity for S-100 (b). Old haemorrhages in the tumour (c). Low proliferation rate of the tumour (Ki-67, d). Complete absence of EMA staining in the tumour (e)

Postoperative recovery

Immediately after the surgery, the sensory and motor functions of the patient were intact. During the inpatient stay, the patient had a veritable postoperative course; the sensory impairments remained unchanged. Postoperative MRI of the cervical spine confirmed complete removal of the intramedullary lesion. Interestingly, the massive spinal cord edema decreased almost completely within 10 days after surgery (Fig. 1). The patient was discharged to medical rehabilitation. Follow-up examination 4 months after surgery revealed favourable, unchanged neurological condition (modified McCormick scale: grade I).

Material and methods

For this study, no experiments on human subjects or animals have been carried out. We performed a systematic review of the literature in PubMed, EMBASE and CENTRAL up to January 1, 2020, to retrieve all relevant studies and case reports on IMS. We used the keywords “intramedullary” simultaneous with “schwannoma OR neurinoma”. Selection criteria were the following: (1) at least one histological proven IMS reported, (2) available clinical information of the patient and (3) peer reviewed publication in a journal or book chapter. Studies published in other languages than English were included in order to receive a complete review of all reported cases. Melanotic IMS were excluded because of their reclassification as a distinct entity in 2016 [12]. In a second step, for complete identification, all reported studies on IMS have been analysed regarding additional cases of IMS. Each case which was mentioned in these articles was analysed with respect to our inclusion criteria. If not already found via keyword search, the case was added to our systematic review (Fig. 3).

Fig. 3.

Fig. 3

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Workflow of the systematic review of the literature

Results

One hundred nineteen studies including 165 reported cases met our inclusion criteria. In only five cases, the patients harboured more than one IMS. Gender ratio was nearly 3:2 (male: female; 55.4% male; 39.2% female); mean age of disease presentation was 40.2 years (range 1 day–78 years); eleven patients suffered from NF (6.6%). A closer analysis of patients suffering from NF revealed that one patient had NF type 1, eight patients had NF type 2 and in two cases no information on the NF type was available. Most IMS were located in the cervical (45.8%) and thoracic (37.3%) spine; a smaller number was located in the cervicothoracic (6.2%), thoracolumbar (5.6%) and lumbar (2.3%) spine (Table 1).

Table 1.

Patients’ characteristics, preoperative neurological status, postoperative outcome and follow-up

Case No. Reference Patient Localization Symtpoms OP Recovery McCormick scale* Follow-up
Age Sex NF Vertebra Sensorysystem Motorsystem Autonomicnervous system Duration(months) PräOP PostOP Months McCormickscale* Tumourrecurrence
1 Penfield, 1932 [13] 12 M No C5 Yes Yes No 96 Yes n.a. n.a. n.a. n.a. n.a. n.a.
2 Rasmussen et al., 1940 [14] 12 M No C4–7 n.a. n.a. n.a. 48 Yes – n.a. n.a. n.a. n.a. n.a.
3 Roka, 1951 [15] 30 M No Cerv. n.a. n.a. n.a. 36 Yes n.a. n.a. n.a. n.a. n.a. n.a.
4 Rose, 1954 [16] 61 M NF 1 C5 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
5 Riggs/Clary, 1957 [17] 60 M No C4/5 Yes Yes Yes n.a. Yes – IV IV 24 n.a. No
6 Ramamurthi et al., 1958 [18] 35 M No T2 Yes Yes Yes 9 Yes + V III 48 III Yes
7 Scott/Bentz, 1962 [19] 46 F No T3 Yes Yes No 144 Yes o V V n.a. n.a. n.a.
8 McCormick et al., 1964 [20] 62 M No L2 No No No n.a. No (Autopsy) n.a. n.a. n.a. n.a. n.a. n.a.
9 Sloof, 1964 [9] 62 F No Cerv. Yes No No n.a. No (Autopsy) n.a. n.a. n.a. n.a. n.a. n.a.
Cerv.
Cerv.
10 Mason/Keigher, 1968 [21] 37 M No T8–10 Yes Yes No 3 Yes + III III 6 II No
11 Chigasaki/Pennybacker, 1968 [22] 75 F No T3 Yes Yes No 7 Yes – V V 6 n.a. n.a.
12 Van Duinen, 1971 [23] 24 F No C3 Yes Yes Yes 48 Yes + III IV 3 II No
13 Fabres et al., 1972 [24] 26 M No T2/3 Yes Yes No 13 Yes + IV IV n.a. n.a. n.a.
14 Cambier et al., 1974 [25] 60 M No C2–4 Yes Yes No 6 Yes – III IV 17 IV No
15 Wood et al., 1975 [26] 48 M No C3 Yes Yes No 3 Yes – IV IV 0 n.a. n.a.
16 Schmitt, 1975 [27] 68 M No L1 Yes Yes No n.a. No (autopsy) n.a. n.a. n.a. n.a. n.a. n.a.
17 Isu et al., 1976 [28] 30 F No C1 Yes Yes No 6 Yes n.a. III n.a. n.a. n.a. n.a.
18 Kumar/Gulati, 1977 [29] 24 F NF Cerv. Yes Yes No 12 Yes o V V n.a. n.a. n.a.
T7–9
19 Vailati et al., 1979 [30] 40 F No T8/9 No Yes No 12 Yes + IV IV 6 II No
20 Gegalian, 1979 [31] 37 F No T10/11 Yes Yes No n.a. Yes + IV IV 120 II No
21 Pardatscher et al., 1979 [8] 41 M No T2–8 Yes Yes Yes 6 Yes – IV III n.a. n.a. n.a.
T8 n.a.
22 Shalit/Sandbank, 1981 [32] 21 F No C2-T2 Yes Yes No 6 Yes + IV III 18 II No
23 Guidetti, 1967 [33], Cantore et al., 1982 [34] 54 F No C3–5 Yes Yes No 24 Yes + II I n.a. n.a. n.a.
24 57 M No T12–L1 No No No n.a. Yes + I I n.a. n.a. n.a.
25 Lesoin et al., 1983 [35] 45 F No C3–7 No No No 6 Yes + n.a. II n.a. n.a. n.a.
26 28 M No L1 No Yes Yes 50 Yes + n.a. III 11 II No
27 Rout et al., 1983 [36] 50 F No C3–5 Yes Yes Yes 60 Yes + III III 12 II No
28 Kang/Song, 1983 [37] 47 M No C3–6 Yes Yes No 12 Yes + IV III 6 II No
29 Bouchez et al., 1984 [38] 34 M No C2–7 Yes Yes No 12 Yes – II II 60 IV No
30 Drapkin et al., 1985 [39] 30 F No C3–5 Yes Yes No 46 Yes + II I 20 I No
31 Lesoin et al., 1986 [40] 75 M No T3–6 Yes Yes Yes 60 Yes + IV III 6 III No
32 Maruki et al., 1986 [41] 42 F No T7/8 Yes Yes No n.a. Yes + n.a. n.a. n.a. n.a. n.a.
33 Ross et al., 1986 [4] 67 F No C2–T1 Yes Yes Yes 48 Yes + II I 6 I No
34 36 M No C4/5 Yes Yes No 4 Yes ++ II I n.a. n.a. n.a.
35 Char/Cross, 1987 [42] 54 M No T3/4 Yes Yes Yes 1 Yes – II I 0 n.a. n.a.
36 Garen et al., 1988 [43] 30 F No C3–6 Yes Yes Yes 24 Yes + II II n.a. n.a. n.a.
37 Hida et al., 1988 [44] 72 F No T8/9 Yes Yes Yes 132 Yes n.a. n.a. n.a. n.a. n.a. n.a.
38 Okuda et al., 1988 [45] 23 M No Med.–C7 Yes Yes No n.a. Yes + IV III 6 III No
39 Gorman et al., 1989 [46] 15 F No C5/6 Yes Yes No 8 Yes + II III 5 II No
40 Sharma et al., 1989 [47] 10 M No C5 Yes Yes Yes 12 Yes + IV III 6 II No
41 Meisel et al., 1990 [48] 36 M No T9/10 Yes Yes Yes 36 Yes ++ III II 2 I No
42 Li/Holtas, 1991 [49] 67 F n.a. C2 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
43 Herregodts et al., 1991 [50] 49 F No T2 No Yes Yes 60 Yes + III III 2 II No
44 Jacquet et al., 1992 [51] 44 M No T12 – L1 No No No 5 Yes ++ I I n.a. n.a. n.a.
45 Morimoto et al., 1992 [52] 42 M No T7–9 No Yes No 13 Yes ++ II I n.a. n.a. n.a.
46 Benini et al., 1993 [53] 40 M No T7–9 Yes Yes Yes 36 Yes + III IV 5 II No
47 43 M No C5/6 Yes No Yes 60 Yes – I IV 12 IV No
48 Sekerci et al., 1993 [54] 30 F No T1–3 Yes Yes No 4 Yes o II IV 6 II No
49 Radhakrishnan et al., 1993 [55] 50 F No C2–5 Yes Yes No 60 Yes + IV II 12 II No
50 55 M No C4–6 Yes Yes No 12 Yes + II II 3 II No
51 Nicoletti et al., 1994 [56] 47 F No C3–5 No Yes No 6 Yes + V III 12 n.a. No
52 Duong et al., 1995 [57] 34 M No T5–7 No Yes No 18 Yes ++ II I 60 n.a. Yes
53 53 F No T11–L2 No Yes No 24 Yes – II V 36 V Yes
54 Melancia et al., 1996 [58] 39 F No T8 Yes Yes No 8 Yes + II n.a. 18 I No
55 Lee et al., 1996 [2] 31 F NF 2 C5–T3 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. 12 II n.a.
56 Bhayani/Goel, 1996 [6] 15 M NF C4/5 No Yes No 18 Yes + III II 2 I No
C5 No
57 Botelho et al., 1996 [59] 52 F No C4–6 Yes Yes No 48 Yes + III n.a. 12 II No
58 Innocenzi et al., 1996 [60] 44 M No C1–3 No Yes No 18 Yes ++ II II 24 I No
59 Bekar et al., 1997 [61] 40 M No C2–T1 Yes Yes Yes 60 Yes n.a. II III 12 III No
60 Beşkonakli et al., 1997 [62] 42 F No T8 Yes Yes No 12 Yes + III II 12 II No
61 Chitoku et al., 1998 [63] 26 M NF2 T4/5 Yes Yes No n.a. Yes o III III n.a. n.a. n.a.
62 Kotil et al., 1998 [64] 20 F NF 2 T10/11 n.a. n.a. n.a. n.a. Yes – n.a. n.a. 0 n.a. n.a.
63 Hejazi/Hassler, 1998 [65] 65 M No T12–L1 Yes Yes Yes 120 Yes ++ n.a. n.a. n.a. n.a. No
64 Binatli et al., 1999 [66] 9 M No C6–T1 Yes Yes Yes 4 Yes ++ II I 3 I No
65 Arellanes-Chávez et al., 2000 [67] 18 M No C2–5 No Yes No 36 Yes + II II n.a. n.a. n.a.
66 Riffaud et al., 2000 [3] 25 M No C1/2 Yes Yes No 12 Yes + III III 12 II No
67 Ogunbgo et al., 2000 [68] 24 M No C4–7 Yes Yes No 36 Yes + III n.a. 18 II No
68 Kodama et al., 2000 [69] 37 F No C3–5 Yes Yes No 108 Yes + n.a. n.a. n.a. n.a. n.a.
69 17 F No C1 Yes Yes Yes 12 Yes + n.a. n.a. n.a. n.a. n.a.
70 Patronas et al., 2001 [70] 26 n.a. NF 2 n.a. n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
71 Kono et al., 2001 [71] 59 M No T2 Yes Yes No 6 Yes + n.a. n.a. n.a. n.a. n.a.
72 Maira et al., 2001 [72] 69 M No C2 Yes Yes Yes n.a. Yes ++ III I 36 n.a. No
73 Sasaki et al., 2002 [73] 53 M NF 2 C5/6 Yes Yes No n.a. Yes + II II n.a. n.a. n.a.
74 Darwish et al., 2002 [74] 68 F No C3/4 Yes Yes No 108 Yes o II II n.a. n.a. n.a.
75 Brown et al., 2002 [75] 51 F No T3–8 Yes Yes No 24 Yes + III IV 6 III No
76 O’Brien et al., 2003 [76] 48 M No T11–L1 Yes Yes No 6 Yes ++ I I 6 I No
77 Colosimo et al., 2003 [77] 59 M No C2 Yes Yes No 12 Yes ++ n.a. n.a. 48 I No
78 47 F No T8 No Yes No 12 Yes + n.a. III 36 II No
79 Panagiotopoulos et al., 2004 [78] 71 M No T6 Yes Yes No 12 Yes ++ IV II 36 I No
80 51 M No T9/10 Yes Yes No 3 Yes + IV II n.a. n.a. n.a.
81 Siddiqui/Shah, 2004 [79] 13 F NF 2 Med.–C3 Yes Yes No 6 Yes + III n.a. 3 II No
82 Conti et al., 2004 [80] 28 F NF 2 C1 Yes Yes Yes n.a. Yes n.a. IV n.a. n.a. n.a. n.a.
83 31 F No C4–6 n.a. n.a. n.a. 72 Yes + n.a. n.a. n.a. n.a. Yes
84 44 M No T10 n.a. n.a. n.a. 36 Yes + n.a. n.a. n.a. n.a. No
85 Chavez-Lopez et al., 2004 [81] 40 M No C4–6 Yes Yes No 24 Yes + II I n.a. n.a. n.a.
86 El Malki et al., 2005 [82] 40 F No C1–6 Yes Yes No 84 Yes + n.a. n.a. 6 n.a. No
87 Amato et al., 2005 [83] 38 F No C4 Yes No No 1 Yes + n.a. n.a. 36 I No
88 Matsuyama et al., 2009 [84], Kim et al., 2005 [85] 72 F No T8/9 Yes Yes No 10 Yes + II II n.a. n.a. n.a.
89 Kyoshima et al., 2005 [86] 54 M No T9/10 Yes Yes Yes 48 Yes + II III 60 II No
90 Shenoy/Raja, 2005 [87] 29 M No C4–7 Yes Yes Yes 36 Yes + n.a. n.a. n.a. n.a. n.a.
91 Kahilogullari et al., 2005 [88] 38 F No T12–L2 Yes No No 7 Yes ++ I I n.a. n.a. n.a.
92 Ho et al., 2006 [89] 45 M No C5/6 No No No n.a. Yes + I I 4 I No
93 Mukerji et al., 2007 [90] 8 M No C5–7 Yes Yes Yes 6 Yes + V n.a. 18 I No
94 Hida et al., 2008 [91] 41 M No C1/2 Yes Yes Yes 6 Yes + n.a. n.a. n.a. n.a. n.a.
95 30 M No C5–7 Yes Yes No n.a. Yes + n.a. n.a. n.a. n.a. n.a.
96 Kim et al., 2009 [92] 11 F No T5/6 Yes Yes Yes 9 Yes – II IV 138 III No
97 Nicácio et al., 2009 [93] 40 M No C4–6 Yes Yes Yes 24 Yes + III III 24 III No
98 Hayashi et al., 2009 [94] 78 F No T11–L1 Yes Yes No 240 Yes o II III 10 III No
99 Ohtonari et al., 2009 [95] 29 M No T12–L1 No Yes Yes 8 Yes ++ II I n.a. n.a. n.a.
100 Adam et al., 2010 [96] 21 F No C2–5 Yes Yes No 18 Yes ++ II I 12 I No
101 46 F No T2–6 n.a. n.a. n.a. 6 Yes + III n.a. 48 n.a. No
102 Lyle et al., 2010 [97] 0 M No T2–Sacr. Yes Yes n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
103 Bernal-García et al., 2010 [5] 35 F No T1–5 Yes Yes Yes 36 Yes + III n.a. 204 II No
104 18 F NF 2 C5–7 Yes Yes No 24 Yes + III n.a. n.a. II No
Med.–C5 No
105 Teo et al., 2011 [98] 44 M No C5/6 Yes Yes No 24 Yes + II I n.a. n.a. n.a.
106 Ryu et al., 2011 [99] 68 M No T6/7 Yes Yes No 17 Yes + III III 1 II No
107 Vij et al., 2011 [100] 25 M No T10/11 Yes Yes Yes 36 Yes – III IV n.a. n.a. n.a.
108 Das et al., 2012 [101] 55 M No C2/3 No No No n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
109 Li et al., 2013 [102] 42 M No T10/11 Yes Yes Yes 18 Yes + IV IV 18 I No
110 Lee et al., 1999 [103], Lee et al., 2013 [104] 39 F No C4–7 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
111 41 F No C5/6 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
112 49 F No C5–7 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
113 46 F No T1/2 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
114 19 F No T6–8 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
115 42 M No T7/8 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
116 60 M No T7–10 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
117 44 M No T8/9 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
118 37 F No T9/10 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
119 78 M No T10/11 n.a. n.a. n.a. n.a. Yes + n.a. n.a. n.a. n.a. No
120 Eljebbouri et al., 2013 [105] 10 M No T7–9 Yes Yes Yes 6 Yes + III n.a. 18 I No
121 Wu et al., 2011 [106], Yang et al., 2014 [107] 52 M No C6–T4 No Yes Yes 120 Yes o III III 154 III No
122 41 F No C4–6 No Yes No 6 Yes ++ II III 140 I No
123 39 M No C3–5 Yes No No 12 Yes ++ I I 125 I No
124 35 M No C6 Yes No No 36 Yes ++ I II 114 I No
125 46 M No T3–5 Yes Yes No 12 Yes + III III 102 II No
126 61 M No C6/7 Yes No No 24 Yes ++ II I 94 I No
127 42 M No T10–12 Yes No No 24 Yes ++ III II 85 I No
138 31 M No C3/4 Yes No No 12 Yes ++ II I 78 I No
129 56 F No C5/6 Yes Yes No 36 Yes ++ II III 74 I No
130 60 F No T2/3 Yes No No 36 Yes ++ II I 65 I No
131 48 M No T9/10 Yes Yes Yes 144 Yes + III IV 58 III No
132 59 M No C1/2 Yes No No 36 Yes ++ I III 54 I No
133 50 F No C5/T1 Yes No No 24 Yes ++ II III 51 I No
134 57 M No C4–6 No No No 6 Yes ++ II II 47 I No
135 44 F No C5–7 No Yes No 48 Yes ++ II II 41 I No
136 44 M No T3 Yes Yes No 12 Yes ++ II II 24 I No
137 40 M No C3 Yes No No 2 Yes ++ II II 20 I No
138 34 M No T12 No Yes No 48 Yes ++ II II 16 I No
139 17 M No T6–8 Yes No No 12 Yes ++ II III 12 I No
140 38 M No T11 Yes No Yes 18 Yes ++ III II 6 I No
141 Yang et al., 2015 [108] 35 M No T11/12 Yes Yes Yes 24 Yes ++ II II 3 I No
142 Gupta et al., 2015 [109] 48 M No C3/4 Yes Yes No 5 Yes + III III 12 II No
143 Jagannatha et al., 2016 [110] 11 M No T11/12 Yes Yes Yes 12 Yes ++ III n.a. 6 n.a. No
144 Sun et al., 2017 [111] 24 M n.a. C1/2 Yes Yes Yes 6 Yes + II I n.a. n.a. n.a.
145 Nayak et al., 2017 [112] 28 M No T1–9 Yes Yes Yes 36 Yes + IV III n.a. n.a. n.a.
146 Gao et al., 2017 [113] 34–59 6 M 2 F No T8/9 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
147 No T9/10 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
148 No T10 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
149 No T4–6 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
150 No T10/11 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
151 No C6–T1 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
152 No C5/6 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
153 No C4–7 n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. n.a. n.a. n.a.
154 Karatay et al., 2017 [114] 30 F No T12/L1 No Yes No 2 Yes + II n.a. n.a. n.a. n.a.
155 Li et al., 2017 [115] 30 M No C3–5 No No No 1 No (autopsy) n.a. n.a. n.a. n.a. n.a. n.a.
156 Navarro Fernández et al., 2018 [116] 19 M No C6–7 Yes Yes No 36 Yes + IV IV 1 III No
157 Landi et al., 2018 [117] 8 F No T10/11 Yes Yes No 8 Yes ++ III II 84 I No
158 Singh et al., 2018 [118] 27 F No T12–L2 Yes Yes Yes 12 Yes + III III 6 III No
159 Wang et al., 2018 [119] 9 M No T8 Yes Yes No 6 Yes ++ II I 36 I No
160 Shi et al., 2019 [120] 42 F n.a. Cerv. n.a. n.a. n.a. n.a. Yes n.a. n.a. n.a. 36 n.a. n.a.
161 Dhake/Chatterjee, 2019 [121] 10 M No T10–12 Yes Yes Yes 6 Yes + III n.a. 216 V Yes
162 57 F No T9/10 Yes Yes No 24 Yes + IV n.a. 24 III Yes
163 Dai et al., 2019 [122] 34 M No C3/4 Yes Yes No 24 Yes ++ I I 12 I No
164 Sekar et al., 2019 [123] 37 F No C5–7 Yes Yes Yes 12 Yes n.a. II n.a. n.a. n.a. n.a.
165 Kelly et al., 2020 [124] 43 M No C4-T2 Yes Yes No 18 Yes + V V 3 IV No
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*Modified McCormick scale

n.a. information not available

NF neurofibromatosis

OP operation

We reviewed the included cases with respect to preoperative neurological status, the postoperative outcome and the follow-up, including tumour recurrence. In addition, we calculated the modified McCormick scale to determine the neurological status preoperatively and postoperatively. The analysis of preoperative neurological symptoms showed that sensory disturbance appeared in 67%, motor deficits in 68% and dysfunction of the autonomic nervous system, such as sphincter dysfunction, in 26% of the cases. The main duration of symptoms was 29 months. The preoperative neurological status according to the modified McCormick scale showed the following distribution: grade I (6%), grade II (27%), grade III (21%), grade IV (12%) and grade V (4%); in 30% of the cases, the preoperative modified McCormick scale was not determinable (Table 1).

Our review showed that 161 of 165 patients underwent surgery; in four cases, the diagnosis of IMS was made postmortem by autopsy. The analysis of the postoperative recovery revealed that complete recovery was achieved in 23%, symptom improvement in 51% and stable neurological condition in 4% of the cases. The neurological symptoms worsened in only 4% of cases and in another 4% the patient died after surgery. Information on the postoperative recovery was missing in 14% of the cases. The postoperative neurological status according to the modified McCormick scale showed the following distribution: grade I (16%), grade II (16%), grade III (19%), grade IV (10%) and grade V (3%); in 36% of the cases, the postoperative modified McCormick scale was not determinable (Table 1).

Additionally, we examined the postoperative outcome depending on the duration of symptoms. We defined “long duration of symptoms” as a duration of symptoms for more than 10 years. Patients with IMS and a duration of symptoms of < 10 years recovered completely in 23%, improved in 52% and were in stable neurological condition in 3% of cases; 5% these patients had worsening of symptoms and 4% died after operation. Patients with IMS and a duration of symptoms of ≥ 10 years recovered completely in only 17%, improved in 17% and were in stable neurological condition in 50%; none of these patients had worsening of symptoms or died after operation. Information on the postoperative outcome depending on the duration of symptoms was not determinable in 13% of the patients with a symptom duration < 10 years and in 16% of the patients with a symptom duration of ≥ 10 years.

The average duration of follow-up on a patient with IMS was 34 months. Tumour recurrence was only observed in 4% of the cases (Table 1).

Information on MRI images were available in only half of the cases. In the available T1-weighted images, most cases showed an isointense (18.1%) or hypointense (16.9%) imaging pattern; mixed (6.8%) and hyperintense (6.2%) patterns were observed less frequently. T2-weighted images showed in 23.2% a hyperintense, in 11.9% an isointense, in 8.5% a mixed and in 7.9% a hypointense pattern. All cases showed a gadolinium enhancement, which was homogenous in 32.8%, heterogenous in 18.6%, some cases showed only a circular (5.6%) and 2 cases were reported to only show minimal gadolinium enhancement (1.1%). 17.5% of the IMS showed a cystic component. Perifocal edema was observed in 22% of the cases; 20.9% of cases were associated with syringomyelia (Table 2).

Table 2.

Radiological findings

Case No. Reference Localization MRI
Vertebra T1 T2 GA CYS OE SYX
1 Penfield, 1932 [13] C5 n.a. n.a. n.a. n.a. n.a. n.a.
2 Rasmussen et al., 1940 [14] C4–7 n.a. n.a. n.a. n.a. n.a. n.a.
3 Roka, 1951 [15] Cerv. n.a. n.a. n.a. n.a. n.a. n.a.
4 Rose, 1954 [16] C5 n.a. n.a. n.a. n.a. n.a. n.a.
5 Riggs/Clary, 1957 [17] C4/5 n.a. n.a. n.a. n.a. n.a. n.a.
6 Ramamurthi et al., 1958 [18] T2 n.a. n.a. n.a. n.a. n.a. n.a.
7 Scott/Bentz, 1962 [19] T3 n.a. n.a. n.a. n.a. n.a. n.a.
8 McCormick et al., 1964 [20] L2 n.a. n.a. n.a. n.a. n.a. n.a.
9 Sloof, 1964 [9] Cerv. n.a. n.a. n.a. n.a. n.a. n.a.
Cerv. n.a. n.a. n.a. n.a. n.a. n.a.
Cerv. n.a. n.a. n.a. n.a. n.a. n.a.
10 Mason/Keigher, 1968 [21] T8–10 n.a. n.a. n.a. n.a. n.a. n.a.
11 Chigasaki/Pennybacker, 1968 [22] T3 n.a. n.a. n.a. n.a. n.a. n.a.
12 Van Duinen, 1971 [23] C3 n.a. n.a. n.a. n.a. n.a. n.a.
13 Fabres et al., 1972 [24] T2/3 n.a. n.a. n.a. n.a. n.a. n.a.
14 Cambier et al., 1974 [25] C2–4 n.a. n.a. n.a. n.a. n.a. n.a.
15 Wood et al., 1975 [26] C3 n.a. n.a. n.a. n.a. n.a. n.a.
16 Schmitt, 1975 [27] L1 n.a. n.a. n.a. n.a. n.a. n.a.
17 Isu et al., 1976 [28] C1 n.a. n.a. n.a. n.a. n.a. n.a.
18 Kumar/Gulati, 1977 [29] Cerv. n.a. n.a. n.a. n.a. n.a. n.a.
T7–9 n.a. n.a. n.a. n.a. n.a. n.a.
19 Vailati et al., 1979 [30] T8/9 n.a. n.a. n.a. n.a. n.a. n.a.
20 Gegalian, 1979 [31] T10/11 n.a. n.a. n.a. n.a. n.a. n.a.
21 Pardatscher et al., 1979 [8] T2–8 n.a. n.a. n.a. n.a. n.a. n.a.
T8 n.a. n.a. n.a. n.a. n.a. n.a.
22 Shalit/Sandbank, 1981 [32] C2-T2 n.a. n.a. n.a. n.a. n.a. n.a.
23 Guidetti, 1967 [33] Cantore et al., 1982 [34] C3–5 n.a. n.a. n.a. n.a. n.a. n.a.
n.a. n.a. n.a. n.a. n.a. n.a.
24 T12 – L1 n.a. n.a. n.a. n.a. n.a. n.a.
25 Lesoin et al., 1983 [35] C3–7 n.a. n.a. n.a. n.a. n.a. n.a.
26 L1 n.a. n.a. n.a. n.a. n.a. n.a.
27 Rout et al., 1983 [36] C3–5 n.a. n.a. n.a. n.a. n.a. n.a.
28 Kang/Song, 1983 [37] C3–6 n.a. n.a. n.a. n.a. n.a. n.a.
29 Bouchez et al., 1984 [38] C2–7 n.a. n.a. n.a. n.a. n.a. n.a.
30 Drapkin et al., 1985 [39] C3–5 n.a. n.a. n.a. n.a. n.a. n.a.
31 Lesoin et al., 1986 [40] T3–6 n.a. n.a. n.a. n.a. n.a. n.a.
32 Maruki et al., 1986 [41] T7/8 n.a. n.a. n.a. n.a. n.a. n.a.
33 Ross et al., 1986 [4] C2–T1 Iso. Hyper. n.a. n.a. n.a. n.a.
34 C4/5 n.a. n.a. n.a. n.a. n.a. n.a.
35 Char/Cross, 1987 [42] T3/4 n.a. n.a. n.a. n.a. n.a. n.a.
36 Garen et al., 1988 [43] C3–6 n.a. Hyper. n.a. n.a. n.a. n.a.
37 Hida et al., 1988 [44] T8/9 n.a. n.a. n.a. n.a. n.a. n.a.
38 Okuda et al., 1988 [45] Med.–C7 n.a. n.a. n.a. n.a. n.a. n.a.
39 Gorman et al., 1989 [46] C5/6 Mixed Hyper. n.a. No No No
40 Sharma et al., 1989 [47] C5 n.a. n.a. n.a. n.a. n.a. n.a.
41 Meisel et al., 1990 [48] T9/10 Hyper. Hypo. Homo. No Yes Yes
42 Li/Holtas, 1991 [49] C2 Hypo./Iso. Iso./Hypo. Homo. No Yes No
43 Herregodts et al., 1991 [50] T2 Hyper. n.a. Homo. No Yes No
44 Jacquet et al., 1992 [51] T12–L1 n.a. n.a. Homo. n.a. n.a. n.a.
45 Morimoto et al., 1992 [52] T7–9 n.a. n.a. n.a. n.a. n.a. n.a.
46 Benini et al., 1993 [53] T7–9 n.a. Hyper. Minimal No No No
47 C5/6 n.a. Iso. Homo. No No Yes
48 Sekerci et al., 1993 [54] T1–3 n.a. n.a. n.a. n.a. n.a. n.a.
49 Radhakrishnan et al., 1993 [55] C2–5 n.a. n.a. n.a. n.a. n.a. n.a.
50 C4–6 n.a. n.a. n.a. n.a. n.a. n.a.
51 Nicoletti et al., 1994 [56] C3–5 Hyper. Hypo. n.a. No No No
52 Duong et al., 1995 [57] T5–7 Iso. Iso. Homo. Yes Yes Yes
53 T11–L2 n.a. n.a. n.a. n.a. n.a. n.a.
54 Melancia et al., 1996 [58] T8 Hypo. Hypo. Homo. No No Yes
55 Lee et al., 1996 [2] C5–T3 n.a. n.a. n.a. n.a. n.a. n.a.
56 Bhayani/Goel, 1996 [6] C4/5 n.a. n.a. Homo. n.a. n.a. n.a.
C5 n.a. n.a. Homo. n.a. n.a. n.a.
57 Botelho et al., 1996 [59] C4–6 n.a. n.a. Homo. Yes No Yes
58 Innocenzi et al., 1996 [60] C1–3 Hypo. Hyper. Homo. No No No
59 Bekar et al., 1997 [61] C2-T1 Hyper. Hyper. Homo. Yes No No
60 Beşkonakli et al., 1997 [62] T8 Hyper. n.a. n.a. No Yes No
61 Chitoku et al., 1998 [63] T4/5 Hypo. Iso. n.a. n.a. n.a. Yes
62 Kotil et al., 1998 [64] T10/11 n.a. Hyper. n.a. n.a. n.a. n.a.
63 Hejazi/Hassler, 1998 [65] T12–L1 n.a. n.a. n.a. n.a. n.a. n.a.
64 Binatli et al., 1999 [66] C6–T1 n.a. n.a. Homo. n.a. n.a. Yes
65 Arellanes-Chávez et al., 2000 [67] C2–5 Iso. Hyper. Homo. Yes No Yes
66 Riffaud et al., 2000 [3] C1/2 Hyper. Hypo. Homo. No Yes No
67 Ogunbgo et al., 2000 [68] C4–7 n.a. n.a. Heter. No No Yes
68 Kodama et al., 2000 [69] C3–5 Hyper. Iso./Hypo. Homo. No Yes No
69 C1 Hypo. Hyper. Circ. Yes Yes Yes
70 Patronas et al., 2001 [70] n.a. n.a. n.a. n.a. n.a. n.a. n.a.
71 Kono et al., 2001 [71] T2 Iso. Iso./Hyper. Homo. Yes Yes No
72 Maira et al., 2001 [72] C2 n.a. n.a. Homo. No No No
73 Sasaki et al., 2002 [73] C5/6 Hypo. Iso. n.a. n.a. n.a. n.a.
74 Darwish et al., 2002 [74] C3/4 n.a. n.a. Homo. No No No
75 Brown et al., 2002 [75] T3–8 n.a. n.a. Heter. No No Yes
76 O’Brien et al., 2003 [76] T11–L1 n.a. Hyper. n.a. Yes No No
77 Colosimo et al., 2003 [77] C2 Iso. Hypo. Homo. No Yes No
78 T8 Iso. Hyper. Homo. Yes Yes No
79 Panagiotopoulos et al., 2004 [78] T6 Hypo. Hyper. Homo. No No No
80 T9/10 Hypo. Hyper. Homo. Yes No No
81 Siddiqui/Shah, 2004 [79] Med.–C3 Iso/Hypo. Hyper. Heter. No No Yes
82 Conti et al., 2004 [80] C1 n.a. n.a. n.a. n.a. n.a. n.a.
83 C4–6 n.a. n.a. n.a. n.a. n.a. n.a.
84 T10 n.a. n.a. n.a. n.a. n.a. n.a.
85 Chavez-Lopez et al., 2004 [81] C4–6 Iso. Iso./Hyper. Homo. No Yes No
86 El Malki et al., 2005 [82] C1–6 Hyper. Hyper. Heter. Yes No Yes
87 Amato et al., 2005 [83] C4 Hyper.  n.a. Homo. No No Yes
88 Matsuyama et al., 2009 [84] Kim et al., 2005 [85] T8/9 n.a. Iso. Homo. No Yes No
89 Kyoshima et al., 2005 [86] T9/10 Iso./Hypo. Iso. Circ. No No No
90 Shenoy/Raja, 2005 [87] C4–7 Iso./Hypo. Hyper. Circ. No No Yes
91 Kahilogullari et al., 2005 [88] T12–L2 n.a. n.a. Heter. n.a. n.a. n.a.
92 Ho et al., 2006 [89] C5/6 Iso. Hyper. Homo. No No No
93 Mukerji et al., 2007 [90] C5–7 Iso. Hyper. n.a. No Yes No
94 Hida et al., 2008 [91] C1/2 Hypo. Iso. Heter. No Yes No
95 C5–7 n.a. n.a. Homo. No No No
96 Kim et al., 2009 [92] T5/6 Hypo. Iso. Circ. No No Yes
97 Nicácio et al., 2009 [93] C4–6 Hyper. Hypo. Heter. No Yes Yes
98 Hayashi et al., 2009 [94] T11–L1 Hypo. Iso. Circ. Yes Yes No
99 Ohtonari et al., 2009 [95] T12–L1 Iso. n.a. Homo. Yes No No
100 Adam et al., 2010 [96] C2–5 n.a. n.a. n.a. n.a. n.a. n.a.
101 T2–6 n.a. n.a. n.a. n.a. n.a. n.a.
102 Lyle et al., 2010 [97] T2–Sacr. n.a. Iso. Heter. No No No
103 Bernal-García et al., 2010 [5] T1–5 Iso. Hyper. Homo. No Yes No
104 C5–7 Hyper. Iso. Homo No No No
Med.–C5 n.a. n.a. n.a. Yes No No
105 Teo et al., 2011 [98] C5/6 Hypo. Hyper. Homo. Yes Yes No
106 Ryu et al., 2011 [99] T6/7 Iso. Hyper. Homo. No Yes Yes
107 Vij et al., 2011 [100] T10/11 Hypo. Iso. n.a. No No No
108 Das et al., 2012 [101] C2/3 Hypo. Hyper. n.a. No No Yes
109 Li et al., 2013 [102] T10/11 Iso. Hypo. Heter. No Yes No
110 Lee et al., 1999 [103], Lee et al., 2013 [104] C4–7 n.a. n.a. Heter. n.a. n.a. n.a.
111 C5/6 n.a. n.a. Homo. n.a. n.a. n.a.
112 C5–7 n.a. n.a. Homo. n.a. n.a. n.a.
113 T1/2 n.a. n.a. Homo. n.a. n.a. n.a.
114 T6–8 n.a. n.a. Homo. n.a. n.a. n.a.
115 T7/8 n.a. n.a. Circ. n.a. n.a. n.a.
116 T7–10 n.a. n.a. Heter. n.a. n.a. n.a.
117 T8/9 n.a. n.a. Circ. n.a. n.a. n.a.
118 T9/10 n.a. n.a. Homo. n.a. n.a. n.a.
119 T10/11 n.a. n.a. Homo. n.a. n.a. n.a.
120 Eljebbouri et al., 2013 [105] T7–9 n.a. Hyper. Heter. Yes Yes No
121 Wu et al., 2011 [106], Yang et al., 2014 [107] C6-T4 Hypo./Iso. Hyper. Heter. Yes Yes No
122 C4–6 Hypo. Hyper. Homo. No No Yes
123 C3–5 Iso. Iso. Homo. No No Yes
124 C6 Hypo. Hyper. Homo. No No Yes
125 T3–5 Hypo./Iso. Hyper. Heter. Yes Yes No
126 C6/7 Hypo. Hyper./Iso. Circ. Yes No No
127 T10–12 Hypo./Iso. Hyper./Iso. Heter. Yes No No
138 C3/4 Iso. Iso. Heter. No No No
129 C5/6 Hypo. Hyper. Heter. Yes Yes No
130 T2/3 Iso. Iso. Homo. No No Yes
131 T9/10 Iso. Hyper. Homo. No No Yes
132 C1/2 Iso. Iso. Homo. No No Yes
133 C5/T1 Hypo. Hyper./Iso. Heter. Yes Yes No
134 C4–6 Hypo./Iso. Hyper. Heter. Yes Yes No
135 C5–7 Iso. Hyper./Iso. Heter. No No Yes
136 T3 Iso. Iso. Homo. No Yes No
137 C3 Iso. Hyper. Heter. No No Yes
138 T12 Iso. Hyper./Iso. Heter. Yes No Yes
139 T6–8 Iso. Hyper./Iso. Heter. Yes No Yes
140 T11 Iso. Iso. Homo. No No No
141 Yang et al., 2015 [108] T11/12 Iso. Hypo. Heter. Yes No Yes
142 Gupta et al., 2015 [109] C3/4 n.a. Iso. Heter. Yes Yes No
143 Jagannatha et al., 2016 [110] T11/12 Hyper./Hypo. Hypo. Heter. Yes No Yes
144 Sun et al., 2017 [111] C1/2 Iso. Iso. Homo. No No Yes
145 Nayak et al., 2017 [112] T1–9 Hypo. Hyper. Homo. Yes No No
146 Gao et al., 2017 [113] T8/9 Iso. Hypo./Hyper. Heter. No Yes No
147 T9/10 Hypo. Hypo. Heter. No Yes No
148 T10 Iso. Hypo. Heter. No Yes Yes
149 T4–6 Hypo. Hyper. Homo. No No No
150 T10/11 Hypo. Hypo. Homo. No Yes No
151 C6–T1 Hypo. Hypo./Hyper. Homo. No Yes Yes
152 C5/6 Hypo. Hypo./Hyper. Homo. No Yes No
153 C4–7 Hypo. Hypo./Hyper. Homo. No No No
154 Karatay et al., 2017 [114] T12/L1 Hypo. Hyper. Homo. No No Yes
155 Li et al., 2017 [115] C3–5 n.a. n.a. n.a. n.a. n.a. n.a.
156 Navarro Fernández et al., 2018 [116] C6–7 Iso. Hyper. Circ. Yes Yes No
157 Landi et al., 2018 [117] T10/11 n.a. Hypo. Homo. No No No
158 Singh et al., 2018 [118] T12–L2 Hypo./Hyper. Hyper. Heter. Yes No No
159 Wang et al., 2018 [119] T8 Hypo. iso Homo. No No Yes
160 Shi et al., 2019 [120] Cerv. n.a. n.a. n.a. n.a. n.a. n.a.
161 Dhake/Chatterjee, 2019 [121] T10–12 Iso./Hypo. Hyper. Heter. No No No
162 T9/10 Hypo. Hyper. Circ. No No No
163 Dai et al., 2019 [122] C3/4 Iso. Hyper. Minimal No Yes No
164 Sekar et al., 2019 [123] C5–7 Hypo. Hyper. n.a. Yes Yes No
165 Kelly et al., 2020 [124] C4–T2 Iso./Hypo. Hyper. Heter. No No Yes
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MRI magnetic resonance imaging

T1 T1-weighted images

T2 T2-weighted images

GA gadolinium enhanced

CYS cystic lesion

OE oedema in T2-weighted images

SYX tumour-associated syringomyelia

iso. isointense

Hypo. hypointense

Hyper. hyperintense

Homo. homogenous

Heter. heterogenous

Circ. ciruclar

n.a. information not available

Discussion

To our knowledge, no complete review of all reported cases has been performed thus far. Here, we attempted to gather all reported cases since 1932. Interestingly, we found more cases than previously described in other series [62, 80, 98]. Due to the language barrier, reports in Japanese, Chinese, French, Portuguese, German and Spanish were not included in previous reports. Additionally, keyword research in the known databases did not show all cases; further analysis of reported case series revealed cases, which were missed by keyword research of the databases. This series of 166 cases including our own study is the largest review of cases on IMS. An uncomplete review of this very rare pathology might constitute a limitation, which impacts the estimated epidemiology.

IMS represent 0.3–1.5% of all spinal schwannomas [2–4]. Several studies described a gender distribution of 3:1 (male:female) [93, 107, 113]. Our results showed a higher rate of female patients and thus a gender distribution of 3:2 (male:female). Previous studies found the mean age of disease presentation to be in the fourth decade of life [92, 113, 117]. The mean age of disease presentation in our series was 40.2 years (range: 1 day–78 years old). Thus, the analysis of our series confirmed the previously reported results. The cervical spine followed by the thoracic spine was reported as the most common localization of IMS [3, 85, 88, 89]. These findings are also consistent with our analysis.

Previous studies addressing the clinical features and surgical outcome of patients with IMS revealed sensory disturbance as the most common initial symptom [107]. Our results show that patients with IMS suffer from sensory deficits as often as from motor deficits, but we agree with Yang et al. on the value of sphincter dysfunction as a late symptom [107]. Overall, patients with IMS seem to benefit from operation, which is clearly shown by an improved postoperative neurological status in 86% of the patients. Previous studies on IMS observed that patients with a longer symptom duration benefit less from surgery due to chronical compression of the neuronal tissue by the tumour [107]. In our review, we were not able to confirm this hypothesis, since the analysis of the postoperative outcome as a function of the duration of symptoms revealed no significantly worse outcome for patients with a symptom duration ≥ 10 years. In most of the cases, gross total resection can be achieved easily [107]. In cases in which the tumour is strongly adherent to the surrounding neuronal tissue, subtotal resection should be considered in order to avoid deterioration of the neurological status. In particularly complicated cases, two-stage surgery provides a possible approach towards better therapeutical results [91].

Conti et al. stated that IMS associates with NF; however, several studies showed a prevalence of 0–2% in spinal tumours [7, 70, 80, 103, 125]. Our review found NF in 11 of 166 cases (6.6%). These results reveal slightly higher rates of NF in patients with IMS than previously described; however, no firm association between NF and IMS was found.

IMS are frequently misdiagnosed as another tumour entity because of the tumour location and its heterogenous appearance in MRI diagnostics [113, 122]. Several series described the MRI appearance of schwannomas as being iso/hypointense in the T1- and hyperintense in the T2-weighted images [1]. However, the T1- and T2-weighted appearance of IMS varies among studies [107, 113]. The summary of these studies in our review reveals that in most cases, IMS show a similar MRI appearance as schwannomas. Specifically, in T1-weighted images, 35% of all cases appeared iso- or hypointense and in T2-weighted images, 23.2% were hyperintense. Interestingly, 1/5 of all cases associated with syringomyelia and in 20%, a perilesional edema was observed. The treated patient in our institution suffered from a perilesional edema, which showed a complete remission in the follow-up MRI after 4 months.

The pathogenesis of IMS is controversially debated among experts because of the absence of Schwann cells within the central nervous system (CNS) in healthy individuals [69]. Currently, there are six hypotheses regarding the origin of IMS: (a) conversion of pial mesodermal cells into neuroectodermal Schwann cells [126]; (b) migration and late neoplastic growth of ectopic Schwann cells during embryonal development [18, 30]; (c) origin from Schwann cells from the perivascular nerve plexus surrounding the blood vessels within the CNS [17, 27, 36, 127, 128]; (d) schwannosis in proximity to the anterior spinal artery [129]; (e) centripetal growth from a dorsal nerve root entry zone into the spinal cord [20, 21, 26, 128] and (f) result from imperfect regeneration of the spinal cord after mechanical trauma or chronic disease [130].

Although some association of proliferating vessels around the tumour [4, 32, 35, 68, 102], tumour connection to a nerve root [4, 27, 34, 43, 46, 52, 58, 68, 71, 76, 77, 84, 89, 99, 104, 107, 109, 115, 123] or chronic disease of the spinal cord could be observed in reported cases [39, 100, 107], it is still not possible to make a general statement regarding the pathogenesis of IMS. In our case, a tumour connection to the nerve root could be observed in the MRI of the cervical spine. This is why we rather support the hypothesis of centripetal growth from a nerve root entry zone into the spinal cord as a possible pathomechanism for development of IMS. However, this mechanism is not able to explain the formation of multiple IMS. The special subgroup of multiple IMS might have implications for the pathomechanism of IMS, but the available information do not allow a conclusions about differences in the pathogenesis of singular and multiple IMS.

As part of the preoperative examination and consultation of patients with intramedullary tumours, it is important to make a correct tentative diagnosis to ensure the best possible treatment. Since IMS are benign tumours of the spinal cord, their treatment might differ from other tumours, like spinal astrocytoma or ependymoma. Patients with IMS show a low rate of tumour recurrence. Even in cases with subtotal tumour resection, tumour recurrence is not necessarily observed [107]. In contrast, for patients with spinal ependymoma, the gross total resection is the gold standard to achieve the longest possible progression-free survival [131–134]. Therefore, complete removal of the tumour should be the goal of the surgery. Furthermore, it is unclear if patients with spinal astrocytoma benefit from gross total resection as patients with spinal ependymoma do [135–138]. Additionally, gross total resection is difficult to achieve in patients with spinal astrocytoma without causing a worse neurological outcome, which is why the primary goal of surgery is to spare the surrounding nervous tissue [139, 140]. Unfortunately, spinal astrocytoma and ependymoma are difficult to distinguish from IMS by use of MRI [107, 113, 141]. Therefore, it seems to be important to differentiate intramedullary tumours during surgery with the aid of intraoperative frozen sections in order to provide the patient with the best possible therapy [95, 104].

Conclusion

IMS are rare tumours of the spinal cord. One hundred sixty-six cases have been reported so far, including the here reported case. IMS are more frequently found in male patients; the mean age of disease presentation is the fourth decade of life. The most common localization of IMS is the cervical spine, followed by the thoracic spine. Although several explanations regarding the pathogenesis of IMS have been proposed, it is still not possible to make a general statement regarding the pathogenesis of these tumours, especially for the subgroup of patients with multiple IMS. In our study, no firm association between NF and IMS was found.

Patients suffering from IMS present in most of the cases with sensory and motor deficits; sphincter dysfunction seems to be a late symptom. Due to heterogenous imaging patterns in MRI, it is difficult to preoperatively differentiate an IMS from other intramedullary tumours. Therefore, intraoperative frozen section might be useful to determine the tumour entity and the best suited surgical strategy. Overall, patients with IMS seem to benefit from operation; in most of the cases, gross total resection can be achieved easily. Nevertheless, further multicentre studies are necessary to elucidate the pathomechanism leading to IMS formation and to determine strategies for the best clinical care for these patients.

Acknowledgements

The authors thank Dr. Milad Neyazi for the translation of Japanese publications.

Code availability

Not applicable.

Author’s contributions

All mentioned authors contributed to the study conception and design. Literature search and data collection were performed by VMS. Data analysis and writing of the first manuscript draft were performed by VMS and BN. All authors commented on previous versions of the manuscript and approved the final manuscript.

Funding

Open Access funding provided by Projekt DEAL.

Data availability

The authors declare that the data supporting the findings of this study are available within the article.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Consent to participate

Patient consent was obtained.

Consent for publication

Patient consent was obtained.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Data Availability Statement

The authors declare that the data supporting the findings of this study are available within the article.

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