MEDULLOBLASTOMAS AND POSTERIOR FOSSA SYNDROME

Because medulloblastomas are the most common malignant pediatric brain tumor and the tumor type most commonly associated with posterior fossa syndrome, they will be discussed in greater detail here. The peak incidence of medulloblastoma is around 6 years of age

TABLE 19.12 COMMON LATE SYMPTOMS OF PEDIATRIC CENTRAL NERVOUS SYSTEM TUMORS

COMMON LATE SYMPTOMS OF PEDIATRIC CENTRAL NERVOUS SYSTEM TUMORS

(112). Some conditions such as ataxia telangiectasia, Rubinstein-Taybi syndrome, Turcot syndrome, Gorlin syndrome, and Li-Fraumeni syndrome are associated with increased risk of medulloblastoma (99). Children typically present with ataxia and discoordination (115).

TABLE 19.13 CHEMOTHERAPY NEUROLOGIC SIDE EFFECTS

CHEMOTHERAPY NEUROLOGIC SIDE EFFECTS

Medulloblastoma is a primitive neuroectodermal tumor (PNET) (101). There are different subtypes of medulloblastoma identified by gene expression patterns and also different histologic subtypes (99). These subtypes help stage the tumor clinically, which helps determine which treatment protocol to use. Additionally, the amount of residual tumor and the presence of metastatic disease help determine whether the tumor is considered standard or high risk. Metastatic disease is identified in approximately 30% of cases and disseminates along the CSF pathway (99). Metastases outside of the CNS are very rare (99). Current therapy includes maximal safe tumor resection and craniospinal radiation with adjuvant chemotherapy (112). The surgical goal is maximal resection with reduction of mass effect and restoration of CSF flow, while minimizing the damage to the neuroanatomy (99). Current protocols for standard-risk disease have over an 80% cure rate (112). Unfortunately, relapsed medulloblastoma carries a dismal prognosis (112). The treatment for medulloblastoma (as is true of other tumor types) can lead to extensive neurologic sequelae that can worsen over time (99,120). Table 19.14 details some of the reported consequences (99,108,119-122).

Medulloblastomas need to be distinguished from other PNETs and atypical teratoid rhabdoid tumors (ATRT) (123). In the past, these three tumors were classified together. Newer research demonstrates that they are distinct entities. PNETs often occur supratentorially and can be differentiated from medulloblastomas based on their genetic profile (123). They also carry a worse prognosis than medulloblastomas. ATRTs are very aggressive tumors that tend to affect the very young (124). Most patients with ATRT die within a year of diagnosis (123).

TABLE 19.14 NEUROLOGIC SEQUELAE OF MEDULLOBLASTOMA TREATMENT

NEUROLOGIC SEQUELAE OF MEDULLOBLASTOMA TREATMENT

Posterior fossa syndrome, a consequence of approximately 25% of posterior fossa tumor resections, is very common in medulloblastoma (99,125). It was first described in 1979 in children with medulloblastoma (126). The literature often used the term cerebellar mutism to describe the temporary loss of speech postoperatively (127). For a time, the term "mutism and subsequent dysarthria" was employed to describe the transient mutism followed by severe dysarthria that eventually resolved (128). With the recognition that children also experienced neurobehavioral and emotional problems, as well as dysphagia, decreased initiation of voluntary movements, and other neurologic problems, the term posterior fossa syndrome was adopted (129). Emotional liability (including apathy and irritability), ataxia, axial hypotonia, and brainstem dysfunction all commonly occur in posterior fossa syndrome (125,128). Children may also have cranial nerve findings and substantial dysphagia (99,125). Usually children have a period of normal speech followed by mutism, which manifests between 1 and 2 days after surgery (115,130). Children tend to experience variable recovery, with some children having persistent symptoms beyond 1 year (99,125,130). The recovery of speech typically includes dysarthric monotonous and ataxic speech with subsequent language disturbances such as agrammatism, word finding difficulties, lack of verbal initiative (adynamic language), and reading and writing difficulties (128).

The pathogenesis of posterior fossa syndrome has not been fully elucidated (99,115,128). That being said, splitting the cerebellar vermis and damage to the dentate-thalamic-cortical tracks are associated with posterior fossa syndrome (99,125,130). Hypoperfusion is also a potential culprit (128). The cerebellum is involved in many of the complicated neural functions of the brain including equilibrium, movement, attention, memory and other cognitive functions, and emotional control (115). Although more commonly reported in adults, children with cerebellar damage may be considered to have cerebellar cognitive-affective syndrome characterized by executive dysfunctions, mood disturbances, visual-spatial difficulties, and language impairments (128,131). There is considerable overlap between posterior fossa syndrome and cerebellar cognitive-affective syndrome, which can lead to confusion of terms. In general, posterior fossa syndrome is the acute syndrome that occurs very shortly after posterior fossa surgery (128). Refinement of the definitions of mutism and subsequent dysarthria, posterior fossa syndrome, and cerebellar cognitive-affective syndrome is warranted as is continued research into the etiologies of these conditions.

 
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