Neurochirurgie 61 (2015) 275–278
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Clinical case
Biphasic response of a tecto-mesencephalic pilocytic astrocytoma after Gamma Knife surgery – A case report Réponse biphasique d’un astrocytome pilocytique tecto-mésencéphalique après radiochirurgie par Gamma Knife – à propos d’un cas C. Tuleasca a,b,c,j,∗ , L. Negretti d,e , V. Magaddino f,j , P. Maeder g,j , B. Lhermitte h,j , F.-X. Borruat i,j , M. Levivier a,j a
Neurosurgery service, Gamma Knife center, CHU Vaudois, Lausanne, Switzerland Medical image analysis laboratory (MIAL), CHU Vaudois, Lausanne, Switzerland c École politechnique fédérale de Lausanne, signal processing laboratory (LTS 5), Lausanne, Switzerland d Radiation oncology service, CHU Vaudois, Lausanne, Switzerland e Radiation oncology department, Clinica Luganese, Lugano, Switzerland f Institute of radiation physics, CHU Vaudois, Lausanne, Switzerland g Radiology department, CHU Vaudois, Lausanne, Switzerland h Neuropathology department, CHU Vaudois, Lausanne, Switzerland i Unité de neuro-ophtalmologie, service universitaire d’ophtalmologie, hôpital ophtalmique Jules-Gonin, Lausanne, Switzerland j Faculty of biology and medicine, university of Lausanne, Lausanne, Switzerland b
a r t i c l e
i n f o
Article history: Received 30 September 2014 Received in revised form 18 November 2014 Accepted 29 November 2014 Available online 10 June 2015 Keywords: Pilocytic astrocytoma Gamma Knife surgery Biphasic response
a b s t r a c t Biphasic response (shrinkage–regrowth–shrinkage) of tumors has never previously been reported in the postoperative course, neither after microsurgery, nor after Gamma Knife surgery (GKS). We present the case of an adult with dorsal midbrain syndrome resulting from a pilocytic astrocytoma centered on the mesencephalic tectum. The tumor extended to the third ventricle and the thalamus. Initially, due to tumor growth, a biopsy was performed and histology established. Later, a ventriculocisternostomy for obstructive hydrocephalus was performed. Finally, GKS was performed, as the tumor continued to grow. After GKS, the lesion exhibited a biphasic response, with a major shrinkage at 3 months, regrowth within the target volume at 6 and 9 months and a second phase of important shrinkage at 12 months, which persisted for the next two years. The possible mechanisms for this particular response pattern are discussed. © 2015 Elsevier Masson SAS. All rights reserved.
r é s u m é Mots clés : Astrocytome pilocytique Radiochirurgie Gamma Knife Réponse biphasique
Une réponse biphasique (diminution initiale de volume–augmentation–diminution de volume) des tumeurs cérébrales n’a pas été rapportée dans les suites postopératoires, que ce soit après microchirurgie, ou après radiochirurgie par Gamma Knife (GK). Nous rapportons le cas d’un patient adulte avec un syndrome mésencéphalique dorsal, due à un astrocytome pilocytique, centré sur le tectum mésencéphalique. La lésion présentait une extension au niveau du troisième ventricule ainsi que du thalamus. Initialement, due à une augmentation volumétrique de la tumeur, une biopsie a été réalisée ; ensuite, une ventriculocisternostomie pour une hydrocéphalie obstructive ; finalement, un traitement par GK a été effectué, car l’astrocytome pilocytique continuait à augmenter. Après la radiochirurgie, la tumeur a présenté une réponse biphasique, avec diminution volumétrique importante à 3 mois, re-augmentation dans le volume cible à 6 et 9 mois et ensuite une phase de diminution majeure à 12 mois, qui a persisté pour les prochains deux ans. Les possibles mécanismes de ce pattern particulier de réponse sont présentés. © 2015 Elsevier Masson SAS. Tous droits réservés.
∗ Corresponding author. Neurosurgery department, Gamma Knife center, Lausanne University Hospital, rue de Bugnon 44-46, BH-08, 1011 Lausanne, Switzerland. E-mail address: [email protected] (C. Tuleasca). http://dx.doi.org/10.1016/j.neuchi.2014.11.014 0028-3770/© 2015 Elsevier Masson SAS. All rights reserved.
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Radiosurgery is used as an alternative or as a combined treatment for numerous lesions of the brain [1]. As a minimally invasive image-guided neurosurgical technique, it is increasingly used in the treatment of deeply situated brainstem tumors, such as metastases [2], arteriovenous malformations [3], cavernomas [4] or focal gliomas [5]. Pilocytic astrocytomas (PA) also benefit from radiosurgery, with a high level of tumor control [1]. Pilocytic astrocytoma is a World Health Organization (WHO) grade I tumor, with a peak of incidence between 5 and 15 years of age [6]. The annual incidence for all ages has been reported to be 2.4–4.8 cases per million people, with no gender predilection. Complete resection is considered to be curative, but cannot always be achieved depending on the localization of the tumor, especially in deep or critical brain areas. Subtotal resection of deep-located tumors occasionally fails to delay tumor progression [7] and there is a need for additional therapy. In this context, several studies have advocated the role of radiation therapy or radiosurgery to control tumor growth [8]. Gamma Knife surgery (GKS) is currently considered in the armamentarium for treating pilocytic astrocytomas as a first or second intention surgical treatment, both in pediatric and adult patients [8–11]. We present the case of an adult with a dorsal midbrain syndrome due to a PA centered on the mesencephalic tectum, without evidence for neurofibromatosis I. We observed a biphasic response (shrinkage–regrowth–shrinkage) after GKS over the next 36 months. 1. Case report 1.1. History and examination A 49-year-old, right-handed man complained of vertical diplopia and gait instability when changing position. Initial neuroophthalmological examination revealed a minimal left ocular tilt reaction (hypotropia of the left eye, left head tilt, conjugate clockwise ocular torsion on fundus examination). There was no restriction of oculomotility but the velocity of upward saccades was mildly reduced. Pupil size was 4 mm on both eyes, without reaction to light but reacting briskly to convergence. Visual function was normal, there was no papilledema, and the patient did not
complain of headaches. The clinical diagnosis was a left ocular tilt reaction and a subtle dorsal midbrain syndrome. MRI examination (Fig. 1a) revealed a lesion centered on the mesencephalic tectum, extending cranially to the third ventricle and the thalamus, predominantly on the left side and measuring 15 mm (lateral), 10 mm (antero-posterior) and 10 mm (vertical). The differential diagnosis included PA, germinoma, lymphoma, pinealocytoma or metastasis (despite the absence of a known cancer). The tumor was not homogenous on T2-weighted images, with patches of hyperintense and hypointense areas; there was a slight perilesional edema within the mesencephalon and the medialventral thalamus; the lesion was not separated from the pineal gland; T1-weighted images after Gadolinium injection showed marked and homogenous contrast enhancement. A “wait-andscan” attitude was firstly decided. MRI and clinical examination were regularly performed. We observed gradual worsening of clinical status. At 6 months, MRI showed a significant increase of the tumor size, with more perilesional edema, and a new necrotic/cystic component without obstructive hydrocephalus. No clinical or neuroradiological changes were observed at 9 months. At 16 months, MRI revealed further volumetric increase, with an associated progression of the marginal hypersignal on the T2weighted images. There was no hydrocephalus. Two monovoxel spectroscopy of the tumor could be performed for the first time (SVS ve 30 15 × 15 × 15 mm) and showed a slight increasing of the choline-creatinine ratio, with a value of 1.3 and a low N-acetylaspartate; this was compatible with a glioma of low or intermediate grade. The diagnosis of germinoma was excluded on the basis of the constant tumoral progression within the previous months. At 17 months, the patient’s oculomotor disturbances worsened. A new MRI was performed and showed further growth of the lesion (Fig. 1b). An uneventful stereotactic biopsy was performed. The anatomo-pathological result was compatible with pilocytic astrocytoma, WHO grade I. The moderate increase of the Choline-creatinine ratio found at MR spectroscopy was somewhat surprising due to the pilocytic astrocytoma histology, but can probably be explained by partial volume effect on CSF and vessels in a brain area recognized to be difficult for MR.
Fig. 1. The MRI (T1-weighted images, sagittal plane) acquired at the moment of discovery (a), biopsy (b), ventriculocisternostomy (c) and GKS (d). L’IRM (séquence en pondération T1 MPRAGE, dans le plan sagittal) réalisé au moment de la découverte (a), biopsie (b), ventriculocisternostomie (c) et radiochirurgie Gamma Knife (d).
C. Tuleasca et al. / Neurochirurgie 61 (2015) 275–278
277
Fig. 2. Serial follow-up MRI (T1-weighted images, sagittal plane) at the moment of (a) and after GKS at 3 (b), 6 (c), 9 (d) (all with superimposed dosimetry, after co-registration in the Leksell GammaPlan, Elekta Instruments, AB, Sweden) and 36 (e) months respectively. Les IRM de suivi (séquence en pondération T1 MPRAGE, dans le plan sagittal) au moment de la radiochirurgie Gamma Knife (a) ainsi qu’à 3 (b), 6 (c), 9 (d) (toutes avec la dosimétrie superposé, après co-registration dans la station Leksell GammaPlan® , Elekta Instruments, AB, Suède) et 36 (e) mois, respectivement.
At 20 months, 3 months after the biopsy, the tumor remained stable. The following month, a successful ventriculostomy was performed for obstructive hydrocephalus, due to further growth of the PA (Fig. 1c). In this context, GKS treatment was decided (Fig. 1d).
Finally, a MRI performed 12 months after GKS revealed significant reduction of the tumor’s size, with almost complete regression of the contrast enhancement. Furthermore, the results of both clinical and radiological examination remained unchanged for the next 24 months (i.e. 3 years after the treatment [Fig. 2e]).
1.2. Gamma Knife surgery and postoperative course GKS was performed with the Leksell Gamma Knife Perfexion® (Elekta Instruments, AB, Sweden) (Fig. 2a). The lesion size was 23 mm (lateral), 17.5 mm (antero-posterior) and 17 mm (vertical) at the time of GKS. The maximum marginal dose was 12 Gy at the 50% prescription isodose. The target volume was 3.5 cc and the prescription isodose volume was of 3.9 cc. The conformity, the selectivity, the Paddick and the gradient index were 0.971, 0.872, 0.847 and 2.564, respectively. Twenty-two isocenters were used (including composite ones). Three months after GKS (Fig. 2b), MRI showed major shrinkage of the tumor, without clinical improvement. Six months after GKS (Fig. 2c), MRI showed new progression of the tumor, within the target volume. Nine months after GKS (Fig. 2d) MRI showed continuous increase of the tumor, within the target volume. As both general and neuro-ophtalmological examination remained unchanged, a “wait-and-scan” attitude was adopted.
2. Discussion Low-grade astrocytomas are currently considered among the most common intra-axial CNS tumors [12]. Most of them grow slowly. Also, the growth potential of some subtypes such as PA decreases progressively with the age of the patient [13]. Usually they are located in the posterior fossa, but also in the region of the optic chiasm and hypothalamus (more often associated with type 1 neurofibromatosis) or, less frequently, within the cerebral hemispheres. Depending on the anatomical and functional localization, if symptomatic or progressive, these tumors should undergo complete surgical excision as a first choice treatment. A progression free survival (PFS) of 82% has been reported at 20 years after surgery [14]. In subtotal resection, chemotherapy, external-beam radiotherapy, radiosurgery or stereotactic intracavitary irradiation using phosphorus-32 (for cystic tumors) should be considered as
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additional therapeutic measures. The best candidates for radiosurgery are progressive, circumscribed PA, located in critical or deep areas of the brain [15]. Some case reports addressed the phenomenon of spontaneous involution of PA, especially concerning those located in the optic pathways, tectal plate and diencephalon [16,17]. This phenomenon could also appear after subtotal surgery or ventriculostomy. Balkhoyor et al. [16] reported two cases of diencephalic PA, with spontaneous involution after partial resection, in the absence of type 1 neurofibromatosis. The authors hypothesized that the possible mechanisms could have been decelerating growth kinetics, induction of apoptosis within the tumor cells, development of host immune reaction, hormone imbalance, thrombosis or occlusion of the tumor vasculature and subsequent necrosis. In their cases, they considered that surgical trauma was apparently the precipitating factor for further involution [16]. Hoffmann et al. [18] assessed 62 cases of children with tumors located on the optic pathway and hypothalamus. They postulated that in some of the patients, the biological effect of surgery led to stabilization or involution and occasionally to complete disappearance of the lesion. However, the type of biphasic pattern response after GKS, as reported in the present case has never been previously reported in the literature. Radiosurgery and particularly GKS are gaining increasing therapeutic awareness for these types of tumors [15,19]. Kano et al. [15] reported a series of 14 adult patients with PA who underwent GKS. They found overall survival after GKS of 100%, 88.9% and 88.9% at 1, 3 and 5 years, respectively; the PFS was 83.9%, 31.5% and 31.5% at the same intervals of time. Patients with prior surgical resection were significantly associated with better PFS, but solid tumors, as in the case of our patient, were not. We previously reported the high tumor control offered by radiosurgery in the treatment of PA [1]. Biphasic response was already reported typically in patients with brain metastasis [20]. However, a biphasic response has not been reported to occur in the treatment of PA, nor other benign tumors. Therefore, after initial good response, regrowth of a PA may suggest biphasic response, and therefore a series of controls might be warranted before concluding on tumor progression and initiating further therapy. Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
References [1] Levivier M. Radiosurgery for brainstem lesions. In: Lozano AM, Gildenberg PL, Tasker R, editors. Textbook of stereotactic and functional neurosurgery, 1. Heidelberg: Springer; 2009. p. 786. [2] Lorenzoni JG, Devriendt D, Massager N, Desmedt F, Simon S, Van Houtte P, et al. Brain stem metastases treated with radiosurgery: prognostic factors of survival and life expectancy estimation. Surg Neurol 2009;71:188–95 [discussion 195, 186–95]. [3] Maruyama K, Kondziolka D, Niranjan A, Flickinger JC, Lunsford LD. Stereotactic radiosurgery for brainstem arteriovenous malformations: factors affecting outcome. J Neurosurg 2004;100:407–13. [4] Hasegawa T, McInerney J, Kondziolka D, Lee JY, Flickinger JC, Lunsford LD. Long-term results after stereotactic radiosurgery for patients with cavernous malformations. Neurosurgery 2002;50:1190–7 [discussion 1197–8]. [5] Yen CP, Sheehan J, Steiner M, Patterson G, Steiner L. Gamma Knife surgery for focal brainstem gliomas. J Neurosurg 2007;106:8–17. [6] Arai H. [Brain tumors: the current WHO classification and neuroimagings]. Rinsho Shinkeigaku 2004;44:957–60. [7] Khatib ZA, Heideman RL, Kovnar EH, Langston JA, Sanford RA, Douglas EC, et al. Predominance of pilocytic histology in dorsally exophytic brain stem tumors. Pediatr Neurosurg 1994;20:2–10. [8] Kano H, Niranjan A, Kondziolka D, Flickinger JC, Pollack IF, Jakacki RI, et al. Stereotactic radiosurgery for pilocytic astrocytomas part 2: outcomes in pediatric patients. J Neurooncol 2009;95:219–29. [9] Hallemeier CL, Pollock BE, Schomberg PJ, Link MJ, Brown PD, Stafford SL. Stereotactic radiosurgery for recurrent or unresectable pilocytic astrocytoma. Int J Radiat Oncol Biol Phys 2012;83:107–12. [10] Lizarraga KJ, Gorgulho A, Lee SP, Rauscher G, Selch MT, DeSalles AA. Stereotactic radiation therapy for progressive residual pilocytic astrocytomas. J Neurooncol 2012;109:129–35. [11] Weintraub D, Yen CP, Xu Z, Savage J, Williams B, Sheehan J. Gamma Knife surgery of pediatric gliomas. J Neurosurg Pediatr 2012;10:471–7. [12] Greenberg MS. Primary brain tumors. In: Handbook of neurosurgery. New York: Thieme; 2006. p. 409–14. [13] Ito S, Hoshino T, Shibuya M, Prados MD, Edwards MS, Davis RL. Proliferative characteristics of juvenile pilocytic astrocytomas determined by bromodeoxyuridine labeling. Neurosurgery 1992;31:413–8 [discussion 419]. [14] Forsyth PA, Shaw EG, Scheithauer BW, O’Fallon JR, Layton Jr DD, Katzmann JA. Supratentorial pilocytic astrocytomas. A clinicopathologic, prognostic, and flow cytometric study of 51 patients. Cancer 1993;72:1335–42. [15] Kano H, Kondziolka D, Niranjan A, Flickinger JC, Lunsford LD. Stereotactic radiosurgery for pilocytic astrocytomas part 1: outcomes in adult patients. J Neurooncol 2009;95:211–8. [16] Balkhoyor KB, Bernstein M. Involution of diencephalic pilocytic astrocytoma after partial resection. Report of two cases in adults. J Neurosurg 2000;93:484–6. [17] Gallucci M, Catalucci A, Scheithauer BW, Forbes GS. Spontaneous involution of pilocytic astrocytoma in a patient without neurofibromatosis type 1: case report. Radiology 2000;214:223–6. [18] Hoffman HJ, Humphreys RP, Drake JM, Rutka JT, Becker LE, Jenkin D, et al. Optic pathway/hypothalamic gliomas: a dilemma in management. Pediatr Neurosurg 1993;19:186–95. [19] Hadjipanayis CG, Kondziolka D, Gardner P, Niranjan A, Dagam S, Flickinger JC, et al. Stereotactic radiosurgery for pilocytic astrocytomas when multimodal therapy is necessary. J Neurosurg 2002;97:56–64. [20] Lippitz B, Lindquist C, Paddick I, Peterson D, O’Neill K, Beaney R. Stereotactic radiosurgery in the treatment of brain metastases: the current evidence. Cancer Treat Rev 2014;40:48–59.
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Clinical case
Biphasic response of a tecto-mesencephalic pilocytic astrocytoma after Gamma Knife surgery – A case report Réponse biphasique d’un astrocytome pilocytique tecto-mésencéphalique après radiochirurgie par Gamma Knife – à propos d’un cas C. Tuleasca a,b,c,j,∗ , L. Negretti d,e , V. Magaddino f,j , P. Maeder g,j , B. Lhermitte h,j , F.-X. Borruat i,j , M. Levivier a,j a
Neurosurgery service, Gamma Knife center, CHU Vaudois, Lausanne, Switzerland Medical image analysis laboratory (MIAL), CHU Vaudois, Lausanne, Switzerland c École politechnique fédérale de Lausanne, signal processing laboratory (LTS 5), Lausanne, Switzerland d Radiation oncology service, CHU Vaudois, Lausanne, Switzerland e Radiation oncology department, Clinica Luganese, Lugano, Switzerland f Institute of radiation physics, CHU Vaudois, Lausanne, Switzerland g Radiology department, CHU Vaudois, Lausanne, Switzerland h Neuropathology department, CHU Vaudois, Lausanne, Switzerland i Unité de neuro-ophtalmologie, service universitaire d’ophtalmologie, hôpital ophtalmique Jules-Gonin, Lausanne, Switzerland j Faculty of biology and medicine, university of Lausanne, Lausanne, Switzerland b
a r t i c l e
i n f o
Article history: Received 30 September 2014 Received in revised form 18 November 2014 Accepted 29 November 2014 Available online 10 June 2015 Keywords: Pilocytic astrocytoma Gamma Knife surgery Biphasic response
a b s t r a c t Biphasic response (shrinkage–regrowth–shrinkage) of tumors has never previously been reported in the postoperative course, neither after microsurgery, nor after Gamma Knife surgery (GKS). We present the case of an adult with dorsal midbrain syndrome resulting from a pilocytic astrocytoma centered on the mesencephalic tectum. The tumor extended to the third ventricle and the thalamus. Initially, due to tumor growth, a biopsy was performed and histology established. Later, a ventriculocisternostomy for obstructive hydrocephalus was performed. Finally, GKS was performed, as the tumor continued to grow. After GKS, the lesion exhibited a biphasic response, with a major shrinkage at 3 months, regrowth within the target volume at 6 and 9 months and a second phase of important shrinkage at 12 months, which persisted for the next two years. The possible mechanisms for this particular response pattern are discussed. © 2015 Elsevier Masson SAS. All rights reserved.
r é s u m é Mots clés : Astrocytome pilocytique Radiochirurgie Gamma Knife Réponse biphasique
Une réponse biphasique (diminution initiale de volume–augmentation–diminution de volume) des tumeurs cérébrales n’a pas été rapportée dans les suites postopératoires, que ce soit après microchirurgie, ou après radiochirurgie par Gamma Knife (GK). Nous rapportons le cas d’un patient adulte avec un syndrome mésencéphalique dorsal, due à un astrocytome pilocytique, centré sur le tectum mésencéphalique. La lésion présentait une extension au niveau du troisième ventricule ainsi que du thalamus. Initialement, due à une augmentation volumétrique de la tumeur, une biopsie a été réalisée ; ensuite, une ventriculocisternostomie pour une hydrocéphalie obstructive ; finalement, un traitement par GK a été effectué, car l’astrocytome pilocytique continuait à augmenter. Après la radiochirurgie, la tumeur a présenté une réponse biphasique, avec diminution volumétrique importante à 3 mois, re-augmentation dans le volume cible à 6 et 9 mois et ensuite une phase de diminution majeure à 12 mois, qui a persisté pour les prochains deux ans. Les possibles mécanismes de ce pattern particulier de réponse sont présentés. © 2015 Elsevier Masson SAS. Tous droits réservés.
∗ Corresponding author. Neurosurgery department, Gamma Knife center, Lausanne University Hospital, rue de Bugnon 44-46, BH-08, 1011 Lausanne, Switzerland. E-mail address: [email protected] (C. Tuleasca). http://dx.doi.org/10.1016/j.neuchi.2014.11.014 0028-3770/© 2015 Elsevier Masson SAS. All rights reserved.
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Radiosurgery is used as an alternative or as a combined treatment for numerous lesions of the brain [1]. As a minimally invasive image-guided neurosurgical technique, it is increasingly used in the treatment of deeply situated brainstem tumors, such as metastases [2], arteriovenous malformations [3], cavernomas [4] or focal gliomas [5]. Pilocytic astrocytomas (PA) also benefit from radiosurgery, with a high level of tumor control [1]. Pilocytic astrocytoma is a World Health Organization (WHO) grade I tumor, with a peak of incidence between 5 and 15 years of age [6]. The annual incidence for all ages has been reported to be 2.4–4.8 cases per million people, with no gender predilection. Complete resection is considered to be curative, but cannot always be achieved depending on the localization of the tumor, especially in deep or critical brain areas. Subtotal resection of deep-located tumors occasionally fails to delay tumor progression [7] and there is a need for additional therapy. In this context, several studies have advocated the role of radiation therapy or radiosurgery to control tumor growth [8]. Gamma Knife surgery (GKS) is currently considered in the armamentarium for treating pilocytic astrocytomas as a first or second intention surgical treatment, both in pediatric and adult patients [8–11]. We present the case of an adult with a dorsal midbrain syndrome due to a PA centered on the mesencephalic tectum, without evidence for neurofibromatosis I. We observed a biphasic response (shrinkage–regrowth–shrinkage) after GKS over the next 36 months. 1. Case report 1.1. History and examination A 49-year-old, right-handed man complained of vertical diplopia and gait instability when changing position. Initial neuroophthalmological examination revealed a minimal left ocular tilt reaction (hypotropia of the left eye, left head tilt, conjugate clockwise ocular torsion on fundus examination). There was no restriction of oculomotility but the velocity of upward saccades was mildly reduced. Pupil size was 4 mm on both eyes, without reaction to light but reacting briskly to convergence. Visual function was normal, there was no papilledema, and the patient did not
complain of headaches. The clinical diagnosis was a left ocular tilt reaction and a subtle dorsal midbrain syndrome. MRI examination (Fig. 1a) revealed a lesion centered on the mesencephalic tectum, extending cranially to the third ventricle and the thalamus, predominantly on the left side and measuring 15 mm (lateral), 10 mm (antero-posterior) and 10 mm (vertical). The differential diagnosis included PA, germinoma, lymphoma, pinealocytoma or metastasis (despite the absence of a known cancer). The tumor was not homogenous on T2-weighted images, with patches of hyperintense and hypointense areas; there was a slight perilesional edema within the mesencephalon and the medialventral thalamus; the lesion was not separated from the pineal gland; T1-weighted images after Gadolinium injection showed marked and homogenous contrast enhancement. A “wait-andscan” attitude was firstly decided. MRI and clinical examination were regularly performed. We observed gradual worsening of clinical status. At 6 months, MRI showed a significant increase of the tumor size, with more perilesional edema, and a new necrotic/cystic component without obstructive hydrocephalus. No clinical or neuroradiological changes were observed at 9 months. At 16 months, MRI revealed further volumetric increase, with an associated progression of the marginal hypersignal on the T2weighted images. There was no hydrocephalus. Two monovoxel spectroscopy of the tumor could be performed for the first time (SVS ve 30 15 × 15 × 15 mm) and showed a slight increasing of the choline-creatinine ratio, with a value of 1.3 and a low N-acetylaspartate; this was compatible with a glioma of low or intermediate grade. The diagnosis of germinoma was excluded on the basis of the constant tumoral progression within the previous months. At 17 months, the patient’s oculomotor disturbances worsened. A new MRI was performed and showed further growth of the lesion (Fig. 1b). An uneventful stereotactic biopsy was performed. The anatomo-pathological result was compatible with pilocytic astrocytoma, WHO grade I. The moderate increase of the Choline-creatinine ratio found at MR spectroscopy was somewhat surprising due to the pilocytic astrocytoma histology, but can probably be explained by partial volume effect on CSF and vessels in a brain area recognized to be difficult for MR.
Fig. 1. The MRI (T1-weighted images, sagittal plane) acquired at the moment of discovery (a), biopsy (b), ventriculocisternostomy (c) and GKS (d). L’IRM (séquence en pondération T1 MPRAGE, dans le plan sagittal) réalisé au moment de la découverte (a), biopsie (b), ventriculocisternostomie (c) et radiochirurgie Gamma Knife (d).
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Fig. 2. Serial follow-up MRI (T1-weighted images, sagittal plane) at the moment of (a) and after GKS at 3 (b), 6 (c), 9 (d) (all with superimposed dosimetry, after co-registration in the Leksell GammaPlan, Elekta Instruments, AB, Sweden) and 36 (e) months respectively. Les IRM de suivi (séquence en pondération T1 MPRAGE, dans le plan sagittal) au moment de la radiochirurgie Gamma Knife (a) ainsi qu’à 3 (b), 6 (c), 9 (d) (toutes avec la dosimétrie superposé, après co-registration dans la station Leksell GammaPlan® , Elekta Instruments, AB, Suède) et 36 (e) mois, respectivement.
At 20 months, 3 months after the biopsy, the tumor remained stable. The following month, a successful ventriculostomy was performed for obstructive hydrocephalus, due to further growth of the PA (Fig. 1c). In this context, GKS treatment was decided (Fig. 1d).
Finally, a MRI performed 12 months after GKS revealed significant reduction of the tumor’s size, with almost complete regression of the contrast enhancement. Furthermore, the results of both clinical and radiological examination remained unchanged for the next 24 months (i.e. 3 years after the treatment [Fig. 2e]).
1.2. Gamma Knife surgery and postoperative course GKS was performed with the Leksell Gamma Knife Perfexion® (Elekta Instruments, AB, Sweden) (Fig. 2a). The lesion size was 23 mm (lateral), 17.5 mm (antero-posterior) and 17 mm (vertical) at the time of GKS. The maximum marginal dose was 12 Gy at the 50% prescription isodose. The target volume was 3.5 cc and the prescription isodose volume was of 3.9 cc. The conformity, the selectivity, the Paddick and the gradient index were 0.971, 0.872, 0.847 and 2.564, respectively. Twenty-two isocenters were used (including composite ones). Three months after GKS (Fig. 2b), MRI showed major shrinkage of the tumor, without clinical improvement. Six months after GKS (Fig. 2c), MRI showed new progression of the tumor, within the target volume. Nine months after GKS (Fig. 2d) MRI showed continuous increase of the tumor, within the target volume. As both general and neuro-ophtalmological examination remained unchanged, a “wait-and-scan” attitude was adopted.
2. Discussion Low-grade astrocytomas are currently considered among the most common intra-axial CNS tumors [12]. Most of them grow slowly. Also, the growth potential of some subtypes such as PA decreases progressively with the age of the patient [13]. Usually they are located in the posterior fossa, but also in the region of the optic chiasm and hypothalamus (more often associated with type 1 neurofibromatosis) or, less frequently, within the cerebral hemispheres. Depending on the anatomical and functional localization, if symptomatic or progressive, these tumors should undergo complete surgical excision as a first choice treatment. A progression free survival (PFS) of 82% has been reported at 20 years after surgery [14]. In subtotal resection, chemotherapy, external-beam radiotherapy, radiosurgery or stereotactic intracavitary irradiation using phosphorus-32 (for cystic tumors) should be considered as
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additional therapeutic measures. The best candidates for radiosurgery are progressive, circumscribed PA, located in critical or deep areas of the brain [15]. Some case reports addressed the phenomenon of spontaneous involution of PA, especially concerning those located in the optic pathways, tectal plate and diencephalon [16,17]. This phenomenon could also appear after subtotal surgery or ventriculostomy. Balkhoyor et al. [16] reported two cases of diencephalic PA, with spontaneous involution after partial resection, in the absence of type 1 neurofibromatosis. The authors hypothesized that the possible mechanisms could have been decelerating growth kinetics, induction of apoptosis within the tumor cells, development of host immune reaction, hormone imbalance, thrombosis or occlusion of the tumor vasculature and subsequent necrosis. In their cases, they considered that surgical trauma was apparently the precipitating factor for further involution [16]. Hoffmann et al. [18] assessed 62 cases of children with tumors located on the optic pathway and hypothalamus. They postulated that in some of the patients, the biological effect of surgery led to stabilization or involution and occasionally to complete disappearance of the lesion. However, the type of biphasic pattern response after GKS, as reported in the present case has never been previously reported in the literature. Radiosurgery and particularly GKS are gaining increasing therapeutic awareness for these types of tumors [15,19]. Kano et al. [15] reported a series of 14 adult patients with PA who underwent GKS. They found overall survival after GKS of 100%, 88.9% and 88.9% at 1, 3 and 5 years, respectively; the PFS was 83.9%, 31.5% and 31.5% at the same intervals of time. Patients with prior surgical resection were significantly associated with better PFS, but solid tumors, as in the case of our patient, were not. We previously reported the high tumor control offered by radiosurgery in the treatment of PA [1]. Biphasic response was already reported typically in patients with brain metastasis [20]. However, a biphasic response has not been reported to occur in the treatment of PA, nor other benign tumors. Therefore, after initial good response, regrowth of a PA may suggest biphasic response, and therefore a series of controls might be warranted before concluding on tumor progression and initiating further therapy. Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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