Posterior fossa surgery has a higher incidence of postoperative complications compared to other neurosurgical operations, and a broad variety of typical but also rare adverse events may endanger the patient. Careful observation and the awareness of this fact are always mandatory.

Multiple causes for postoperative airway obstruction after posterior fossa approaches are known. Some of them are related to the patient’s unusual position during surgery. Pharyngeal swelling after intraoperative endotracheal ultrasound [25] or macroglossia after prone position [26, 27] is reported. In soft tissue swelling, antiphlogistics and steroids are indicated.

In uneventful courses, a routine postoperative MRI for assessment of the resection extent must be organized in between 72 h after surgery. Only during this early period no blood-brain barrier disruption other than tumor will allow contrast enhancement [28]. After 3 days, a false-positive contrast uptake will not allow to distinguish between tumor and surgical lesions. This period lasts until 6 weeks postoperatively. Most brain tumor protocols ask for T1 sequences in all three dimensions pre and post contrast. In primarily non-enhancing tumors, T2 and FLAIR sequences are more significant.

In the authors’ experience perioperative EVD has become the exception in posterior fossa tumor surgery, since improved surgical techniques and the possibility of endoscopic third ventriculostomy (ETV) are available [29–35]. In most cases of mild to moderate hydrocephalus, tumor surgery is performed the day after admission without any particular treatment of the hydrocephalus itself, if intraoperative patency of CSF pathways is assured.

In severe symptomatic hydrocephalus without prospect of resolution after tumor surgery and occluded infratentorial CSF spaces, ETV does not seem to be promising and shunting would be performed. Only in emergency situations, the authors would primarily insert an EVD (herniation, bleeding, etc.). This can be done as regular OR procedure or immediately on the ICU with special needle systems [36]. In some centers, perioperative EVD is still a routine for having immediate access to the ventricles in case of sudden ICP rise. In general, a handling guideline for EVD management is recommended in order to avoid related complications.

Once an EVD is in place, weaning should be started as soon as the assumed cause for eventual hydrocephalus or elevated ICP is solved or became unlikely. The first step is to gradually elevate the draining pressure above normal pressure ranges (depending on the patient’s age up to 15 cm H₂O). If no symptoms are overt, closure of the drainage can be attempted with intermediate pressure measurements. Alternatively, continuous ICP monitoring can be performed instead of keeping the drainage open.

Should the intracranial pressure levels remain in normal ranges, removal of the EVD is carried out. In persistent intracranial hypertension, shunting is indicated after or MRI scan to exclude unexpected causes.

In modern series of experienced departments, postoperative complication rate is very low. Typical surgical complications are bleeding into the tumor bed and remote bleeding due to excessive brain slacking mostly after operating in sitting position, e.g., subdural (Fig. 56.2), epidural, or intra-axial hemorrhage [37–41]. But also swelling of cerebellar and brainstem tissue, vascular infarction, and severe pneumocephaly (Fig. 56.3) can be responsible for impairment of neurological functions and indicate further ventilation and special treatment aspiration/drainage [42]. In rare cases, secondary emergency operations are necessary, mainly to remove a clot or to perform posterior fossa decompression. In most cases, re-bleeding after brain tumor resection is caused by tumor remnants that should also be removed if localization allows it. A coagulation disorder must be ruled out as well [43].

Complications related to the CSF system are most frequently seen after posterior fossa surgery. The syndrome of aseptic meningitis is characterized by spiking fever and meningismus. CSF analysis reveals pleocytosis and elevated protein, while cultures remain negative. It counts for up to 25 % of all postoperative complications with the highest rate after tumor surgery [44–46]. Bacterial meningitis is rare, but the immunosuppressive effects of corticosteroids can lead to serious and lethal infections and this fact has to be taken into consideration [47].

Suboccipital pseudomeningoceles (Fig. 56.4) and CSF fistulas also belong to the most frequent complications and occur in 10–25 %. Depending on skin penetration, aseptic or septic meningitis can develop.

Aseptic meningitis is related to certain tumors (10 % in cerebellar astrocytomas) or to the implantation of an artificial dura substitute. The risk of septic meningitis following a CSF fistula is enhanced by steroid medication. Small pseudomeningoceles without progression can be watched and sometimes punctured. In many cases, they resolve spontaneously or remain uncomplicated. CSF fistulas require immediate closure before any deep or CSF infection. In most cases, single compression sutures will solve the problem. Lumbar puncture with the aim to lower the intrathecal pressure, shunting procedures in underlying CSF circulation disorders, and finally secondary revision have to be considered [48, 49].

Not all pseudomeningoceles become clinically apparent. One retrospective series reports about 16 % symptomatic pseudomeningoceles, although a total of 41 % showed CSF accumulations on postoperative MRI at days 1–5. These findings progressively resolved in nearly all patients spontaneously after 10–15 months. The risk to develop a CSF leak was higher in patients with pseudomeningoceles (39 % versus 13 %). Additionally, the hospital stay was markedly prolonged in this patient group. Suboccipital craniectomy compared to craniotomy seemed to be a predisposing factor (69 % versus 38 %) [32, 50].

Unusual surgical complications can be seen as well. Especially, young children with thin calvarial bone can develop epidural hematoma in case of pin penetration in Mayfield fixation, but also air embolism caused by fixation pins in sitting position is described [51]. Surgery in sitting position, e.g., in large tumor masses in the posterior fossa and rapid tumor removal, may lead to tension pneumocephaly, which is always a life-threatening situation with potential for severe neurological damage [52–59]. Rarely compression of a venous sinus by hemostyptic material or bone wax can cause intracranial hypertension [60, 61]. Extradural pneumatocele due to open mastoid cells is also described [62], as well as rhabdomyolysis after operations in sitting position [63].

In another 10-year (1992–2002) retrospective study of all posterior fossa surgeries, data from 500 patients were obtained and the overall complication rate was 31.8 %. Cerebrospinal fluid leaks were the most frequent complication in 13 %, followed by meningitis in 9.2 % and wound infection in 7 %. After tumor surgery cerebellar edema occurred in 5 %, hydrocephalus in 4.6 %, cerebellar hematoma in 3 %, and cerebellar mutism in 1.2 % of patients of all ages.

The authors found that compared to other surgical sites, posterior fossa surgery involves greater morbidity and mortality and has a wider variety of complications [64, 65].

Spinal structures can also be involved in postoperative complications, mainly due to positioning and the given vicinity to the posterior fossa. Cervical instability [66], myelopathy [67], spinal subdural hematoma [68, 69], tetraparesis [70, 71], and spinal cord infarction [72] have been described.

Other rare complications are inverse herniations due to large tumor masses and bradycardia after the instillation of hydrogen peroxide for hemostasis [73, 74].

An orbital emphysema after posterior fossa surgery in sitting position for pilocytic astrocytoma and ETV in a 4-year-old girl is reported [75] as well as cerebral ischemia after venous air embolism [76].

The mortality rate during the early postoperative period is very low and tends toward zero. Morbidity is mainly caused by neurological deficits and is most often transient. Additional new deficits occur in about one third of the patients. Significant persisting impairment is to be expected, when the cranial nerves and brainstem are involved.

Other non-neurological causes for postoperative morbidity are rare in childhood. Cerebellar ataxia is the most common and obvious neurological deficit found pre and post surgically. Depending on the site of the postoperative lesion, different symptoms are found, although in most cases a spatial and functional overlapping exists: Should the neocerebellum (cerebellar hemispheres) are affected, limb ataxia, dysmetria, dysdiadochokinesia, tremor, and muscular hypotension as well as ataxic dysarthria (scanning speech) will occur. Lesions in the paleocerebellum (cerebellar vermis and paravermal zone) lead to truncal ataxia, which is also the case in affections of the archicerebellum (nodulus and flocculus cerebella) that is connected to vestibular neurons. Vertigo and nausea are typical focal symptoms.

Nystagmus is a common finding after posterior fossa surgery as well and follows in irritations or lesions of cerebellar or brainstem structures.

Vomiting can be a side effect of anesthesia or a symptom of a gastric problem, but there are different specific reasons related to posterior fossa surgery: pneumocephaly, raised ICP, and irritation of the area postrema, the brain’s vomiting center located at the obex. Additionally, irritation of the vestibular system also provokes vomiting. Careful indication of antiemetic medication is recommended and persistent vomiting should implicate further diagnostics. Refractory emesis can be life threatening, e.g., in small infants [77].

Brainstem lesions might result in severe cranial nerve deficits and impaired coordination of vital vegetative functions like blood pressure, heart rate, vessel reactivity, breathing, and somatic reflexes (swallowing reflex, gag reflex, cough reflex). Additional long tract affections will give rise to internuclear ophthalmoplegia (dysconjugate gaze) and sensomotoric deficits. A typical nasal and slurry speech is part of a bulbar palsy, too [1, 78, 79]. In these brainstem affections, rapid improvement is not common and permanent impairment is to be considered. In vocal cord paralysis and missing somatic reflexes, early tracheostomy and feeding tube, followed by gastrostomy (percutaneous endoscopic gastrostomy, PEG), become necessary. Early radiographic swallowing assessment prior to oral feeding is recommended by some authors. Furthermore, fiber-optic vocal cord and pharyngeal function can be assessed. A team of neurosurgeon, otolaryngologist, pediatric intensivist, and speech therapist should be involved ensuring optimal management of these dysfunctions [80, 81].

Facial nerve malfunction causes lagophthalmos (Bell’s palsy), and especially during night eye closure is incomplete and the cornea might dry out. Infection and corneal ulcers are typical complications. The affected eye must be protected with overnight monoculus and eye ointment or artificial tears.

Double vision can be a sequel of direct nerve root malfunction or brainstem lesion. If there is no early recompensation of oculomotor function, covering of one eye is necessary. Otherwise, mobilization, e.g., in cerebellar ataxia and vertigo, is not possible, due to the lack of optic control [82]. Another rare complication after cerebellar tumor surgery is a transient cerebellar eye closure (TCES). The pathogenesis is unclear [83].

Tumors affecting the medulla oblongata potentially cause progressive CO2 retention and sleep apnea; therefore, preoperative blood gas analysis is recommended as well as frequent postoperative breathing parameter checkup and close breath monitoring [84, 85].

Cerebellar mutism or posterior fossa syndrome is a complex of multiple symptoms that exclusively occurs after posterior fossa surgery in young individuals. So far, the pathophysiological background is not well understood, but a multifunctional organic genesis is assumed [86–98]. Several observations, regarding the patient’s constellation, allow a risk estimation in advance. The syndrome occurs in up to 20 % of pediatric patients after tumor removal in the posterior fossa. Predisposing factors are medulloblastoma; large tumor mass; midline involvement, e.g., the fourth ventricle and brainstem; and preexisting hydrocephalus (Fig. 56.5a–d) [99–105].

Primary brainstem lesions may also cause mutism [106]. After a period of few hours up to 2 days of normal speech production, the child becomes mute or utters only single words, sometime toneless. Additional dysfunction of oral and pharyngeal muscle coordination is obvious in some patients, and consecutively drinking and eating are no longer possible. Both phenomena have been discussed in the past as psychological reactions to the situation. The fact that the syndrome is only observed after posterior fossa surgery and not after involvement of cerebral hemispheres makes a single psychological cause unlikely. The affected child might react apathetically or be suffering and whining or crying and sometimes rejecting his/her own mother [107]. In most cases, significant truncal ataxia is evident [88–96, 108–112] Visual impairment is also described [113].

The symptoms last for weeks up to months and are followed by a phase of dysarthric speech before spontaneous resolution. Deficient speech up to a certain extent remains in most children, though. In the course of investigations regarding the pathophysiological background of cerebellar mutism, possible neuropsychological functions of the cerebellum have been addressed as well. It is now well accepted that the cerebellum plays an important role in neuropsychological and cognitive processes, e.g., in complex speech functions, and is widely connected with higher cerebral structures [114–118].

Recently, it has been shown that patients with a history of cerebellar mutism bear an increased risk for neurocognitive impairment [119, 120].

So far, no specific treatment is known to influence the course of the syndrome. Therefore, cerebellar mutism should be part of the preoperative information, given to the parents, e.g., in cases of large midline tumors suspective for medulloblastoma. Only a few reports exist describing a positive effect of bromocriptine on cerebellar mutism analogous to the effect on akinetic mutism in Parkinson syndromes, which is also observed in hydrocephalic patients developing an aqueductal syndrome [121–123].

Generally, brain tumors should be treated in an interdisciplinary team and each individual case must be evaluated according to available protocols [124]. In some countries, national boards coordinate treatment protocols and all relevant findings, together with reference pathologies that are obtained and shared with the expert team. Also international working groups and boards exist and will be contacted depending on the pathology. In rare histological tumor entities, individual regimens can be defined together with the pediatric neuro-oncology group.

The aim of this strategy is to assure the most promising treatment option in respect of outcome and quality of life for each individual pediatric tumor patient [125].

Postoperative tumor staging should be performed as soon as possible and starts with contrast MRI in the first 72 h after removal. If not performed prior to surgery, spinal MRI is also necessary in tumor types that tend to spread along the CSF pathways, e.g., medulloblastoma, ependymoma, and some astrocytomas [126]. In case of incomplete tumor resection in the posterior fossa, it must be discussed in the interdisciplinary tumor board, whether second look operation is recommended before starting adjuvant therapy or if a wait-and-watch strategy is feasible. In medulloblastoma, only significant tumor remnants of more than 1.5 cm [2] should be reoperated before further adjuvant therapy, due to better outcome statistics for total resection or near total resection [36, 127]. Ependymoma has a significantly better outcome after complete resection due to poor chemo- and radiosensitivity. Indication for second-look surgery should be generous if the tumor localization and the expected neurological deficits allow this [128–133].

In summary, tumor surgery of the posterior fossa is generally more prone for the development of surgical and neurological complications compared to operative procedures of other localizations. Therefore, the postoperative management should be in the hands of an experienced team, specially dedicated to the care of children with severe neuro-oncological diseases [134].