medulloblastoma ( mb ) is the most common pediatric central nervous system ( cns ) malignancy . arising from cerebellar vermis , it commonly spreads along cerebrospinal fluid ( csf ) pathways , with subarachnoid metastases present in 33% of patients at diagnosis . extraneural metastases ( enm ) occur in only 7% of cases , most often by hematogenous dissemination to bone or lymphatic dissemination to lymph nodes . only 17 cases of mb metastasis to the peritoneum have been reported and csf shunts were present in all 17 cases . yet the role of csf shunts in enm of primary cns tumors remains controversial . we report the first case of concurrent ventriculoperitoneal ( vp ) shunt tract seeding and peritoneal metastasis of mb . the unique distribution and timing of enm development presented in this case provide support for the theory that vp shunts are a conduit for mb spread . a 5-year - old hispanic male presented with one month of nausea , vomiting and headache . brain and spine magnetic resonance imaging ( mri ) showed hydrocephalus and a solid fourth ventricular mass but no leptomeningeal metastases ( figure 1 ) . based on mri appearance , signal homogeneity and diffusion restriction along with absence of calcification , hemorrhage , and foraminal tumor extension distinguished the mass from ependymoma . diffusion restriction and absence of a macrocystic component with mural nodule differentiated it from juvenile pilocytic astrocytoma . patient age , midline tumor location , and absence of a cystic component argued against atypical teratoid - rhabdoid tumor . figure 1sagittal post - gadolinium fat saturated t1-weighted brain magnetic resonance imaging at presentation shows an enhancing fourth ventricular mass ( m ) and an enlarged third ventricle ( arrow ) . sagittal post - gadolinium fat saturated t1-weighted brain magnetic resonance imaging at presentation shows an enhancing fourth ventricular mass ( m ) and an enlarged third ventricle ( arrow ) . lateral ventricles were also enlarged ( not shown ) . before primary tumor resection , a right frontal external ventricular drain ( evd ) was placed for hydrocephalus . surgical approach for primary tumor resection included suboccipital craniotomy and c1 laminectomy with microdissection of the cerebellar vermis and medullary tissue . exposure of the fourth ventricle revealed a vascular , firm , rubbery tumor that was removed piecemeal using electrocauterization and forceps . four days after tumor resection , the right frontal evd was exchanged for a right frontal vp shunt . vp shunt surgery started with removal of the evd and passage of the new ventricular catheter though the preexisting burr hole into the right lateral ventricle . a shunt passer was passed from the abdominal incision to the cranial incision and the peritoneal tubing was threaded through the tract . the ventricular catheter and tunneled body wall tubing were connected to an ultra - small medium pressure medical valve yielding spontaneous flow of clear csf at the abdominal end of the tubing . in postoperative week 3 , the patient returned to the hospital with vomiting , headache and abdominal pain . brain and spine mri revealed interval development of diffuse smooth and nodular leptomeningeal enhancement of the brain and spinal cord , later proven by biopsy to represent leptomeningeal carcinomatosis . a shunt revision was performed for suspected shunt malfunction . the abdomen was opened and the abdominal portion of the shunt was dissected free to facilitate repositioning of the valve and shunt in the subgaleal pocket . the patient began chemoradiotherapy with six weeks of intravenous vincristine and total neuraxis radiation ( 55.8 gy to posterior fossa ; 50 gy to thecal sac ) . a second shunt revision was performed in a manner similar to the first , with re - opening of scalp and abdominal wounds and replacement of the obstructed intracranial portion of the shunt . third ventriculoscopy was performed and a third ventriculostomy was attempted in an effort to prolong the life of the shunt . twelve weeks after primary tumor resection , the patient returned with fever , nausea , vomiting , and a firm 4 cm right lateral thoracoabdominal wall mass adjacent to the vp shunt scar . sonography of the right thoracoabdominal wall showed a row of five heterogeneously hypoechoic masses ( figure 2 ) . on contrast - enhanced abdominopelvic computed tomography ( ct ) , the thoracoabdominal wall masses had high - attenuation and were oriented in a craniocaudal direction along the prior vp shunt tract . peritoneal nodules , thickened and heterogeneously attenuating omentum , and bone marrow hypodensities were also present , consistent with peritoneal and bone marrow metastases ( figure 3 ) . surgical biopsy with immunohistochemical staining of the largest abdominal wall mass revealed a malignant small blue cell tumor , identical to the primary anaplastic medulloblastoma . concurrent csf infection resolved with intravenous vancomycin , and a third vp shunt was placed . the patient was discharged on a new systemic maintenance chemotherapy regimen ( intravenous vincristine , cisplatin , and cyclophosphamide ) . due to progression of metastatic disease , he was referred to hospice 5 months after diagnosis and expired soon after . figure 2contiguous sagittal sonographic images of a palpable mass in the right anterolateral thoracoabdominal wall 12 weeks after primary tumor resection show longitudinal arrangement of five heterogeneously hypoechoic medulloblastoma nodules ( arrows ; biopsy - confirmed ) along a ventriculoperitoneal shunt tract . rib 
  contiguous sagittal sonographic images of a palpable mass in the right anterolateral thoracoabdominal wall 12 weeks after primary tumor resection show longitudinal arrangement of five heterogeneously hypoechoic medulloblastoma nodules ( arrows ; biopsy - confirmed ) along a ventriculoperitoneal shunt tract . rib 
 figure 3contrast - enhanced abdominopelvic computed tomography 12 weeks after primary tumor resection . ( a ) sagittal image shows linear arrangement of four medulloblastoma tumor implants in the thoracoabdominal wall ( arrows ) , corresponding in location to prior ventriculoperitoneal shunt tract . ( b ) axial image shows the largest abdominal wall metastasis ( * ) splaying right - sided anterior abdominal wall muscles . ( c ) omental cake ( * ) , nodular peritoneal tumor implants ( white arrows ) , and bone marrow metastasis in the pelvis ( black arrow ; biopsy - confirmed ) are present concurrently . ( a ) sagittal image shows linear arrangement of four medulloblastoma tumor implants in the thoracoabdominal wall ( arrows ) , corresponding in location to prior ventriculoperitoneal shunt tract . ( b ) axial image shows the largest abdominal wall metastasis ( * ) splaying right - sided anterior abdominal wall muscles . ( c ) omental cake ( * ) , nodular peritoneal tumor implants ( white arrows ) , and bone marrow metastasis in the pelvis ( black arrow ; biopsy - confirmed ) are present concurrently . enm of primary cns tumors is uncommon , with incidence in autopsy series of less than 0.5% . mb is the most likely pediatric cns tumor to result in enm , with bone being the most common site , followed by lymph nodes , liver , lung and muscle . there are reports of subcutaneous mb growth at surgical scars in the head and neck and of mb skin metastases in patients without prior surgery . one case of mb metastases to peritoneum and a lumboperitoneal shunt tract has been reported . mb metastases to a shunt tract without documented peritoneal metastases have also been described . to our knowledge , we report the first case of concurrent metastases of mb to a vp shunt tract and peritoneum . causative and permissive factors of enm of primary cns tumors have been proposed , including tumor cell anaplasia , tumor friability and propensity to metastasize in csf , and tumor ability to invade leptomeninges and blood vessels . iatrogenic disruption of the blood brain barrier during cns surgery is also implicated in enm and is thought to provide tumor cells with direct vascular and lymphatic access . the role of vp shunts in enm remains controversial , due in part to the rarity of enm of primary cns tumors and in part to inherent difficulties in establishing a causative relationship between vp shunts and enm . most cases of enm of primary cns tumors occur in the absence of csf shunts . when enm occurs in the presence of vp shunts , tumor spread is attributed to the shunt in only one third of patients . establishing a relationship between vp shunts and enm is usually based on the pattern of metastatic disease in relation to shunt type and location . development of shunt tract metastasis has been suggested as the most specific finding of direct tumor spread attributable to a shunt . of the 17 reported cases of pediatric peritoneal mb metastases , all occurred in patients with vp ( 16 ) or lumboperitoneal ( 1 ) shunts . to our knowledge , there is no report of peritoneal mb metastases in the absence of a peritoneal shunt , implying that shunts are a necessary permissive factor . mb metastases to lung are three times more common in patients with ventriculoatrial shunts than in patients without such shunts . additionally , pediatric enm develop earlier and are associated with poorer outcomes in shunted patients than in non - shunted patients . linear arrangement of implants along the thoracoabdominal portion of a vp shunt tract and at no other cutaneous or subcutaneous location favors the argument that the shunt was not only a permissive factor but also a conduit for mb dissemination . seeding of the thoracoabdominal wall likely occurred by csf spillage or cellular implantation during shunt placement or revision . in contrast , peritoneal tumor seeding could have occurred at any time during shunt utilization by direct cell migration through the shunt . development of bone marrow metastases is less clearly linked to the shunt and rather suggests concurrent hematogenous tumor spread . hematogenous spread requires disruption of the blood brain barrier and could have resulted from cns surgery , csf shunting or direct venous invasion . in previously reported cases of shunt - related peritoneal mb , over 40% although metastases along vp shunt tracts are rare , radiologists , oncologists , and surgeons should be aware of their potential . differential diagnosis includes inflammatory mass and abscess , which likely would be distinguished by fever , leukocytosis , and physical findings of inflammation . our patient had both shunt infection and metastatic disease , but his thoracoabdominal wall masses lacked fat stranding on ct that is typical of an inflammatory process , and internal doppler flow within his masses was inconsistent with abscess . csf pseudocyst , seroma , and lymphocele could occur along a shunt tract but are differentiated by their cystic appearance and lack of internal flow . most importantly , a linear arrangement of masses in the neck or thoracoabdominal wall in proximity to a shunt or shunt tract is highly suggestive of shunt - related metastases .
we report on a 5-year - old boy with seeding of the peritoneum and a ventriculoperitoneal shunt tract by anaplastic medulloblastoma . 
 the role of ventriculoperitoneal shunting in the spread of primary central nervous system tumors has been controversial . in the case 
 reported here , the unique distribution of tumor implants on ultrasound and multiplanar computed tomography gives further credence to the argument that ventriculoperitoneal shunting is a pathway for extraneural metastases of primary central nervous system tumors .