A primitive neuroectodermal tumor (PNET) is an undifferentiated sarcoma that arises from neural crest cells . These tumors develop in the central nervous system (CNS) or peripherally in soft tissues and bones. Specifically, a peripheral PNET involves organs such as the kidneys , bladder , female genital tract , myocardium, pancreas, retroperitoneum, chest wall, or lungs . These undifferentiated tumors predominantly affect children and adolescents while exhibiting a slight predilection for males . The prognosis of this neoplasm is poor as it is associated with a 5-year survival rate less than 25% .
The patient's manifestations will reflect the affected organ or system. For example, a tumor in the kidney or surrounding tissue may cause symptoms such as gross hematuria and flank pain while an adrenal gland malignancy can produce abdominal and flank pain . Additionally, a tumor in the presacral space may result in foot pain and constipation . Additionally, patients with a pulmonary PNET experience fever, cough, hemoptysis, dyspnea, and chest pain as well as symptoms based on involved neighboring structures . Women with a cervical tumor will exhibit vaginal bleeding, vaginal discharge, lower abdominal pain and urinary features. These patients also have cervical lesions and an enlarged uterus .
As for individuals with CNS neuroectoderm tumors, the features will also be site-specific and may include headaches, emesis, visual changes, epistaxis, cranial neuropathies, lethargy, and other changes in mental status. The physical exam findings may include gait ataxia, papilledema, various palsies, and cerebellar features.
Patients suspected to have a PNET warrant a full evaluation with history, a physical exam, and the appropriate studies.
A biopsy should be obtained whether through a needle or surgical excision. Subsequently, the specimen should be analyzed through diagnostic studies such as light microscopy, immunohistochemistry, and cytogenetic testing. Specifically, light microscopy reveals the characteristic appearance of small round cell tumors . A PNET will stain positively for markers such as CD99, CD 56, NSE, and vimentin . Furthermore, genetic analysis reveals a balanced translocation t(11;22)(q24;q12), which is a hallmark feature of this tumor .
Computed tomography (CT) and magnetic resonance imaging (MRI) are among the techniques used to identify the location, extent, and degree of tumor involvement. Note that advanced disease is common at the time of presentation and hence the patient should be evaluated for potential metastasis. The clinician should perform a bone marrow biopsy, a chest CT scan, a chest radiograph, and possibly a positron emission tomography (PET) scan and technetium 99m bone study.
In CNS cases, the preferred imaging modality is the brain MRI although a brain CT scan takes precedence in emergencies. Note that a lumbar puncture is not performed if there is a mass lesion.
To differentiate between a PNET and a neuroblastoma, urinary catecholamines and their metabolites should be obtained. These tests are negative in patients with PNET.