3rd International Hands-on Cadaver Workshop: Microsurgical Approaches to the Skull Base
December 9 — December 10
December 9 — December 10
They usually remain asymptomatic so they are often diagnosed incidentally during radiological evaluation for other reason 1).
These cysts also can cause dysfunction of specific cranial nerves, including III, IV, VI (to cause diplopia), V (to induce trigeminal neuralgia), VII (to cause congenital or acquired facial paralysis), VIII (to cause hearing loss, tinnitus, vertigo), X (to result in hoarseness and dysphagia) 3) 4) 5).
Gurkas et al. report a patient with cranial nerve palsies and mirror movements found in upper extremities. They postulated that CPA arachnoid cyst compressing the brain stem and the pyramidal decussation may lead to mirror movements 6).
MRI (magnetic resonance imaging) scan techniques have led to CPA arachnoid cysts being more frequently diagnosed and with a higher degree of certainty. The need for further understanding of their natural history as well as for the development of a management rationale has been highlighted with this increased rate of diagnosis.
In the series of Alaani et al. these lesions have a characteristic location in the posterior-inferior aspect of the CPA below the facial and vestibulocochlear nerves. These cysts did not show change in size on repeated MRI scan and the patients’ symptoms did not progress over the period of follow up 7).
The differential diagnosis of an arachnoid cyst of the cerebellopontine angle includes other cystic lesions (epidermoid and neurenteric cyst, cystic acoustic schwannoma).
MRI is helpful in differentiating arachnoid cysts from those cystic lesions. If a pathologic cause of a retrocochlear disorder is suspected in a patient with a unilateral sensorineural hearing loss and tinnitus, MRI should be performed to evaluate the cerebellopontine angle.
On MRI, arachnoid cysts appear as smooth-surfaced lesions that in all magnetic resonance sequences exhibit a signal characteristic of CSF. In contrast, epidermoid cysts show mixed signals on FLAIR images and high signals on diffusion weighted images. Neurenteric cysts present high signals on T1-weighted images and cystic schwannomas show some foci of contrast enhancement on T1-weighted postcontrast images 8) 9).
The optimal surgical management of arachnoid cysts remains controversial.
Although surgery for these entities is controversial, arachnoid cysts can be treated surgically with open craniotomy for cyst removal, fenestration into adjacent arachnoid spaces, shunting of cyst contents, or endoscopic fenestration.
Alaani et al. support a conservative management approach to the majority of these cysts 10).
The definitive treatment for these arachnoid cysts is a retrosigmoid suboccipital craniotomy and microsurgical resection and fenestration of the cyst walls 11).
Olaya et al. report the first case of complete recovery from sensorineural hearing loss and facial weakness following endoscopic fenestration 15).
3 pediatric patients with CPA arachnoid cysts (2 with hearing loss and 1 with recurrent headaches) who underwent neurosurgical treatment at the authors’ institution.
Four pediatric patients were diagnosed with CPA arachnoid cysts at the International Neuroscience Institute during the period from October 2004 through August 2012, and 3 of these patients underwent surgical treatment. The authors describe the patients’ clinical symptoms, the surgical approach, and the results on long-term follow-up. RESULTS One patient (age 14 years) who presented with headache (without hearing deficit) became asymptomatic after surgical treatment. The other 2 patients who underwent surgical treatment both had hearing loss. One of these children (age 9 years) had recent-onset hypacusia and experienced complete recovery immediately after the surgery. The other (age 6 years) had a longer history (2 years) of progressive hearing loss and showed an interruption of the deficit progression and only mild improvement at the follow-up visit.
CPA arachnoid cysts are uncommon in pediatric patients. The indication and timing of the surgical treatment are fundamental, especially when a hearing deficit is present 16).
Alaani et al. present a series of five adult patients with different clinical presentations attributed to CPA arachnoid cysts. These lesions have a characteristic location in the posterior-inferior aspect of the CPA below the facial and vestibulocochlear nerves. These cysts did not show change in size on repeated MRI scan and the patients’ symptoms did not progress over the period of follow up. The findings would support a conservative management approach to the majority of these cysts 17).
Five patients (three male and two female patients) with a mean age of 5.6 years have been operated on at the Department of Neurosurgery, New York University Medical Center, USA. since 1980 till 1997.
All five arachnoid cysts compressed the cerebellum or brain stem. One patient had associated hydrocephalus. Three patients presented with refractory headaches associated with nausea and vomiting. The remaining two patients presented with cerebellar signs. No patient had an initial cranial neuropathy.
All patients underwent a retrosigmoid suboccipital craniotomy and microsurgical resection and fenestration of the cyst walls. One patient underwent two procedures. A cystoperitoneal shunt was inserted at the first operation. After the shunting procedure, the patient’s condition deteriorated; however, after the microsurgical resection and fenestration, his symptoms improved. With a mean 5.2-year follow-up, there has been no evidence of clinical or radiographic recurrence 18).
A 4-year-old boy with global developmental delay, esotropia, moderate aortic root dilation, genu valgum, and in-toeing gait. MRI brain for evaluation of neonatal hypotonia revealed a left cerebellopontine angle arachnoid cyst. He referred on newborn hearing screening, and diagnostic auditory brainstem response (ABR) showed left profound retrocochlear hearing loss. Surgical intervention for the arachnoid cyst was deferred, with spontaneous resolution at age two years without hearing recovery. CMA revealed a novel, de novo 5.1 Mb microdeletion of 22q13.31q13.33 not involving SHANK3, a gene typically deleted in PMS.
As diagnostic sensitivity improves, smaller chromosomal imbalances will be detectable related to milder or different phenotypes. They present two patients with novel deletions of chromosome 22q13 associated with multiple congenital anomalies and features distinct from PMS 19).
A 14-year-old previously healthy girl presented to our outpatient clinic with a 6-weeks history of frontal headache. They typically would start in the occipital region and then radiate bifrontally. The neurological examination was unremarkable. Magnetic resonance imaging revealed an extra-axial bilateral lesion in bilateral cerebellopontine angle, larger on left side. The lesions were homogeneously hypointenese on T1-weighted imaging and hyperintense on T2-weighted imaging without evidence of contrast enhancement and without evidence of restriction on diffusion-weighted imaging. No surgical treatment was indicated.
Bilateral arachnoid cysts of the cerebellopontine angle are very infrequent and the main indication for surgery is the existence of clinical symptoms or neurological deficit coincident with the locations of the cysts 20).
Petscavage et al. present the case of a 49-year-old woman who presented with acute, nonprogressive left sensorineural hearing loss and benign positional vertigo that was associated with an arachnoid cyst of the cerebellopontine angle. The presence of the lesion was documented by MRI examinations that were obtained 7 years apart. Arachnoid cysts at the cerebellopontine angle are usually found incidentally on MRI performed for unrelated reasons. However, if the arachnoid cyst displaces or compresses adjacent cranial nerves, symptoms may result. They review the salient imaging features of arachnoid cysts that allow their differentiation from other lesions of the cerebellopontine angle 21).
Gurkas et al. report a patient with a CPA arachnoid cyst. He presented with cranial nerve palsies and mirror movements found in upper extremities. They postulated that CPA arachnoid cyst compressing the brain stem and the pyramidal decussation may lead to mirror movements, and conclude that mirror movements can be associated with CPA arachnoid cyst 22).
A 71-year old woman presenting with a right hemifacial spasm and an ipsilateral arachnoid cyst. Preoperative magnetic resonance imaging findings suggested a neurovascular compression caused by displacement of the facial-acoustic complex and the anterior inferior cerebellar artery by the cyst. Cyst excision and microvascular decompression of the facial nerve achieved permanent relief. The existing cases of arachnoid cysts causing hemifacial spasm are reviewed and the importance of a secondary neurovascular conflict identification and decompression in these cases is highlighted 23).
Trigeminal Neuralgia in a Child With a Cerebellopontine Angle Arachnoid Cyst 24).
Sharma et al. report two cases of bilateral CPA AC with their pathophysiology and review of literature 25).
Visagan et al. first report a CPA arachnoid cyst causing TGN in a paediatric case 26).
A 62-year-old man complaining of vertigo and progressive hearing loss was diagnosed with an arachnoid cyst at the right cerebellopontine angle based on magnetic resonance imaging (MRI). In this case-report, we used computed tomography (CT) cisternography to determine whether the arachnoid cyst communicated with the cerebrospinal fluid (CSF) space. Differentiating between a noncommunicating and communicating arachnoid cyst is required for presurgical evaluation. CT cisternography is a less used but reliable radiological technique for determining the presence of communication, and could therefore be included in the diagnostic work-up of arachnoid cysts. The patient underwent surgery with fenestration of the arachnoid cyst; his vertigo improved and his hearing was preserved 27).
Superior oblique myokymia (SOM) is a rare disorder with an unclear pathogenesis. We describe a first reported case of chronic disabling SOM in association with a cerebellopontine angle arachnoid cyst, who had a gradual and eventually complete symptomatic resolution 8 months following cyst marsupialisation. Among other aetiologies, SOM may therefore be due to abnormal CSF flow dynamics resulting in structural compromise of the nerve 28).
A 7-month-old infant presented to the hospital with a history of delayed milestones and an abnormal increase in head circumference. Magnetic resonance images and CT scans of the brain showed a large CSF cavity involving the entire brainstem and a right CPA arachnoid cyst causing obstruction of the fourth ventricle and dilation of the lateral and third ventricles. Cerebrospinal fluid diversion was performed by direct communication from the syringobulbia cavity to the left lateral ventricle and from the left lateral ventricle through another ventricular catheter; external ventricular drainage was performed temporarily for 5 days. Communication between the syrinx and arachnoid cyst was confirmed. Clinically, there was a reduction in head circumference, and serial MR imaging of the brain showed a decrease in the size of the syrinx cavity and the ventricle along with opening of the normal CSF pathways. The postoperative course was uneventful, and no further intervention was necessary. On follow-up of the child at 3 years, his developmental milestones were normal. Surgical intervention for this condition is mandatory. The appropriate type of surgery should be performed on the basis of the pathophysiology of the developing syringobulbia 29).
A 47-year-old woman complaining of sharp and lancinating pain in the right periauricular and submandibular areas visited our hospital. Swallowing, chewing, and lying on her right side triggered the pain. Her neurologic examination revealed no specific abnormalities. The results of routine hematologic and blood chemistry studies were all within normal limits. Carbamazepine and gabapentin were given, but her symptoms persisted. Her pain was temporarily relieved only by narcotic pain medication. MRI showed an arachnoid cyst located in the right cerebellomedullary cistern extending to the cerebellopontine cistern. Cyst removal was performed via a right retrosigmoid approach. Lateral suboccipital craniotomy was performed using the right park-bench position. After opening the dura and cerebellopontine angle, the arachnoid cyst was exposed. The arachnoid cyst was compressing the flattened lower cranial nerves at the right jugular fossa. Her symptoms resolved postoperatively. Two months after the operation, she was completely free from her previous symptoms 30).
A rare case of cerebellopontine angle arachnoid cyst manifesting as hemifacial spasm (HFS) is reported. The patient is a 42-year-old woman with 10-month history of left HFS. A preoperative magnetic resonance imaging scan showed a well-demarcated area, hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging, in the left cerebellopontine angle, without contrast enhancement, resembling an arachnoid cyst. METHODS: The cyst was excised with microneurosurgical technique and the facial, vestibular, and acoustic nerves were completely decompressed from the arachnoid wall. RESULTS: The postoperative course was uneventful, and the left HFS disappeared immediately. Histologically, the cyst wall was a typical arachnoidal membrane. Ten months after surgery, the patient is symptom free. CONCLUSION: It is well-known that in approximately 10% of cases, trigeminal neuralgia can be caused by a space-occupying mass. However, the fact that HFS can also be caused by organic lesions as well as neurovascular compression is less well-known. Although the occurrence of tumor compression causing HFS has been previously recognized, cerebellopontine angle cysts have very rarely been described. The observation of a patient with a cerebellopontine angle arachnoid cyst causing HFS prompted us to review the literature relative to HFS caused by an organic lesion rather than neurovascular compression 31).
a patient with a CPA arachnoid cyst who presented with hoarseness (unilateral vocal cord paralysis) and dysphagia secondary to isolated compression of the vagus nerve. This rare presentation of a CPA arachnoid cyst has not been reported previously. CLINICAL PRESENTATION: The patient described is a 50-year-old man who experienced a precipitous onset of hoarseness and dsyphagia. An otolaryngological evaluation revealed right-sided vocal cord paralysis. Brain magnetic resonance images displayed a cystic mass at the right CPA and anterior displacement of the vagus nerve. INTERVENTION: The patient underwent retrosigmoidal craniectomy with cyst fenestration, which was well tolerated. Intraoperatively, Cranial Nerve X was found splayed over the cyst and was consequently decompressed. CONCLUSION: Postoperatively, the patient’s dysphagia completely resolved. However, the results of a laryngeal electromyocardiogram revealed minimal evidence of recovery in the affected vocal fold, and the patient continued to suffer from dysphonia. Although CPA arachnoid cysts are rare, they should be considered when a patient presents with an isolated cranial nerve palsy. Treatment options include cyst fenestration and cranial nerve decompression 32).
A 51 years old female is reported who was diagnosed by IRM of a 4,5 x 2 cm arachnoid cyst, situated on the left cerebello-pontine angle, with tinnitus, hearing loss and vertigo that mimicked a Meniere’s attack. We think thees benign tumors must be included in the differential diagnosis of Meniere’s disease because they can be indistinguishable from it clinically 33).
November 8 — November 11
Pittsburgh, PA, USA
75 % are > 10 mm at time of diagnosis.
The aim of a study was to evaluate the effects of some widely diffused pollutants (i.e. benzene, BZ; bis(2-ethylhexyl) phthalate, DEHP and polychlorinated biphenyls, PCB) on growth hormone secretion, the somatostatin and estrogenic pathways, viability and proliferation of rat GH-producing pituitary adenoma (GH3) cells. All the pollutants induced a statistically significant increase in GH secretion and interfered with cell signaling. They all modulated the expression of SSTR2 and ZAC1, involved in the somatostatin signaling, and the expression of the transcription factor FOXA1, involved in the estrogen receptor signaling. Moreover, all the pollutants increased the expression of the CYP1A1, suggesting AHR pathway activation. None of the pollutants impacted on cell proliferation or viability. Present data demonstrate that exposure to different pollutants, used at in vivo relevant concentrations, plays an important role in the behavior of GH3 pituitary adenoma cells, by increasing GH secretion and modulating several cellular signaling pathways. These observations support a possible influence of different pollutants in vivo on the GH-adenoma aggressiveness and biological behavior 3).
Giant GH-secreting adenomas are invasive, uncontrolled by surgery, and respond poorly to medical treatment. Aggressive multimodal therapy is critical for their management, enhancing control rate and biochemical remission 4).
Co-secretion of growth hormone (GH) and prolactin (PRL) from a single pituitary adenoma is common. In fact, up to 25% of patients with acromegaly may have PRL co-secretion. The prevalence of acromegaly among patients with a newly diagnosed prolactinoma is unknown. Given the possibility of mixed GH and PRL co-secretion, the current recommendation is to obtain an insulin-like growth factor-1 (IGF-1) in patients with prolactinoma at the initial diagnosis. Long-term follow-up of IGF-1 is not routinely done 5).
It is related to high levels of growth hormone (GH) and insulin-like growth factor-I (IGF-1).
T2 weighted image differentiates GH secreting pituitary adenomas into subgroups with particular behaviors. This raises the question of whether T2-weighted signal could represent a factor in the classification of acromegaly in future studies 7).
In patients with acromegaly, T2 weighted image signal intensity at diagnosis correlates with histological features and predicts biochemical outcome of first-line somatostatin analogues (SA) treatment 8).
Each of the biomarkers, Ki-67 and p53, along with patient’s age and mixed GH-prolactin secretion showed a kind of correlation with each of aspects of the clinical, hormonal and radiologic outcome of GH-secreting pituitary adenomas 9).
Surgery is the first-line therapy.
The resection via a transsphenoidal approach is able to induce a long-term remission of acromegaly, with low risk of recurrence and complications. Endoscopic endonasal transsphenoidal approach is more suitable than microscopic technique in macroadenomas and adenomas with suprasellar extension 10).
The most widely used criteria for neurosurgical outcome assessment were combined measurements of IGF-1 and GH levels after oral glucose tolerance test (OGTT) 3 months after surgery. Ninety-eight percent of respondents stated that primary treatment with somatostatin receptor ligands (SRLs) was indicated at least sometime during the management of acromegaly patients. In nearly all centers (96%), the use of pegvisomant monotherapy was restricted to patients who had failed to achieve biochemical control with SRL therapy. The observation that most centers followed consensus statement recommendations encourages the future utility of these workshops aimed to create uniform management standards for acromegaly 13)
Current pharmacotherapy includes somatostatin analogs (SAs) and GH receptor antagonist; the former consists of lanreotide Autogel (ATG) and octreotide long-acting release (LAR), and the latter refers to pegvisomant. As primary medical therapy, lanreotide ATG and octreotide LAR can be supplied in a long-lasting formulation to achieve biochemical control of GH and IGF-1 by subcutaneous injection every 4-6 weeks. Lanreotide ATG and octreotide LAR provide an effective medical treatment, whether as a primary or secondary therapy, for the treatment of GH-secreting pituitary adenoma; however, to maximize benefits with the least cost, several points should be emphasized before the application of SAs. A comprehensive assessment, especially of the observation of clinical predictors and preselection of SA treatment, should be completed in advance. A treatment process lasting at least 3 months should be implemented to achieve a long-term stable blood concentration. More satisfactory surgical outcomes for noninvasive macroadenomas treated with presurgical SA may be achieved, although controversy of such adjuvant therapy exists. Combination of SA and pegvisomant or cabergoline shows advantages in some specific cases. Thus, an individual treatment program should be established for each patient under a full evaluation of the risks and benefits 14).
The standardised mortality index (the ratio of observed mortality in the acromegalic population to expected mortality in the general population) ranged from 1.2 to 3.3. If left untreated, patients with acromegaly can die approximately 10 years earlier than the healthy subjects. According to prior studies, approximately 60, 25 and 15% of the patients die from cardiovascular disease, respiratory complications and cancer, respectively 16)17).
Control of serum GH and insulin-like growth factor (IGF) 1 hypersecretion by surgery or pharmacotherapy can decrease morbidity.
Remission rates for micro- and macroadenomas were 81.8% and 45.8%, respectively. Patients of older age, with a smaller tumor, lower Knosp grade, lower preoperative GH, and insulinlike growth factor 1 levels were more likely to achieve remission. Remission rate decreased significantly with repeat surgeries. Those patients with adenomas that stained positive for somatostatin receptor subtype 2A were less likely to experience tumor recurrence and more likely to respond to medical treatment with persistent or elevated GH hypersecretion 18).
A retrospective review of 53 patients who had follow up endocrinologic data at least 3 months post-surgery was performed among patients who were treated by EEA between 1998 and 2012. Data were analyzed for remission using GH and IGF-I levels based on 2010 consensus criteria. We also analyzed the outcomes using 2000 consensus criteria for ease in comparison to prior studies of outcomes of surgery for acromegaly. In this series of mostly large (88.2% macroadenomas), invasive (46.9% Hardy-Wilson C, D, E) adenomas, there were 27 patients (50.9%) who achieved remission after EEA only. For patients who had no remission with EEA alone, RS and/or medical therapy were used and 37 patients (69.8 %) achieved remission overall. Statistical analysis showed larger tumor size, Hardy Stages C, D, E and Knosp Scores 3, 4 to be predictive against remission for EEA only and EEA with other modalities. The volume of residual tumor after EEA was not found to be predictive of remission with additional therapies. We used stringent consensus criteria from 2010 in a series which included a high proportion of invasive GH secreting adenomas to show that EEA alone or combined with other modalities results in comparable remission rates to earlier studies which used less strict criteria, while retaining low complication rates 19).
Each of the biomarkers, Ki-67 and p53, along with patient’s age and mixed GH-prolactin secretion showed a kind of correlation with each of aspects of the clinical, hormonal and radiologic outcome of GH-secreting pituitary adenomas in the series of Alimohamadi et al. 20).
Her laboratory studies showed markedly elevated levels of Insulin like Growth Factor 1 (IGF-1), and low levels of follicle stimulating hormone and luteinizing hormone. Computerized tomography has revealed a pituitary tumor without extra-sellar extension. The tumor has completely excised via Endoscopic transsphenoidal approach. Histologically, the tumor has diagnosed as a pituitary adenoma with GH positive cells. The serum IGF1 levels have gradually decreased to the normal range and the patient was symptom free for three and a half years when she has returned with complaint of visual impairment. The brain MRI that time has shown a supra-sellar mass growing independently into the remaining sellar part. Subsequently, surgical operation has performed via trans-nasal endoscopic approach. Histopathological and immunohistochemistry examination have revealed a rare case of growth hormone producing pituitary adenoma with brain invasion and lymphocytic infiltration.
The aim of this publication was to present a rare case of growth hormone producing pituitary adenoma with brain invasion and lymphocytic infiltration 21).
Samuel Thomas von Sömmerring (28 January 1755 – 2 March 1830) was a German physician, anatomist, anthropologist, paleontologist and inventor. Sömmerring discovered the macula in the retina of the human eye. His investigations on the brain and the nervous system, on the sensory organs, on the embryo and its malformations, on the structure of the lungs, etc., made him one of the most important German anatomists.
Sömmerring was born in Thorn, Royal Prussia (Toruń, Poland) as the ninth child of the physician Johann Thomas Sömmerring. In 1774 he completed his education in Thorn and began to study medicine at the University of Göttingen. He visited Petrus Camper lecturing at the University in Franeker. He became a professor of anatomy at the Collegium Carolinum (housed in the Ottoneum, now a Natural History Museum) in Kassel and, beginning in 1784, at the University of Mainz. There he was for five years the dean of the medical faculty. Due to the fact that Mainz became part of the French Republic under the French Directory, Sömmerring opened up a practice in Frankfurt in 1795. As one of his many important enterprises, Sömmerring introduced against many resistances the vaccination against smallpox and became one of the first members of the Senckenbergische Naturforschende Gesellschaft and was nominated as counselor. He received offers of employment by the University of Jena and the University of St. Petersburg, but accepted in 1804 an invitation from the Academy of Science of Bavaria, in Munich. In this city, he became counselor to the court and was led into the Bavarian nobility.
He published many writings in the fields of medicine, anatomy and neuroanatomy, anthropology, paleontology, astronomy and philosophy. Among other things he wrote about fossil crocodiles and in 1812 he described Ornithocephalus antiquus now known as Pterodactylus. He was also the first to accurately draw a representation of the female skeleton structure.
In addition, Sömmerring was a very creative inventor, having designed a telescope for astronomical observations and an electrical telegraph in 1809. He worked on the refinement of wines, sunspots and many diverse other things. In 1811 he developed the first telegraphic system in Bavaria, which is housed today in the German Museum of Science in Munich. In 1823, he was elected a foreign member of the Royal Swedish Academy of Sciences.
Sömmering was married to Margarethe Elizabeth Grunelius (deceased 1802), and had a son, Dietmar William, and a daughter, Susanne Katharina. Due to bad weather, Sömmering left Munich in 1820 and returned to Frankfurt, where he died in 1830. He is buried at the city’s main cemetery 1) 2).
When Sömmerring was 23 years old he described the organization of the cranial nerves as part of this doctoral work: its study is valid until today.
The enumeration of the cranial nerves is traced briefly from Galen’s seven to Willis’ ten and to von Sömmerring’s twelve. The system of von Sömmerring, which has been followed for some 200 years, is a useful convention, although it is merely one of several possibilities. The naming of the cranial nerves was standardized nearly 100 years ago 3).
Direct observation at microsurgery of the cerebellopontine angle reveals that CN VII emerges caudal to the CN VIII root from the lower lateral pons rather than the pontomedullary groove. Additionally, the CN VI root lies in the pontomedullary groove caudal to both CN VII and VIII in the vast majority of cases.
In a high-resolution 3D MRI study, the exit location of CN VI was caudal to the CN VII/VIII complex in 93% of the cases. Clearly, Soemmerring’s rostrocaudal numbering system of CN VI-VII-VIII (abducens-facial-vestibulocochlear CNs) should instead be VIII-VII-VI (vestibulocochlear- facial-abducens CNs). While the inaccuracy of the CN numbering system is of note, what is remarkable is that generations of authors have almost universally chosen to perpetuate this ancient error. No doubt some did this through faithful copying of their predecessors. Others, it could be speculated, chose to depict the CN relationships incorrectly rather than run contrary to long-established dogma.
This study is not advocating that a universally recognized numbering scheme be revised, as this would certainly create confusion. The authors do advocate that future depictions of the anatomical arrangements of the brainstem roots of CNs VI, VII, and VIII ought to reflect actual anatomy, rather than be contorted to conform with the classical CN numbering system 4).
July 3 — July 7
Course website: http://www.summerschool-endoscopicskullbase-brescia.com/