Discussion
PNETs occur primarily in children and adolescents; the median age at initial diagnosis is about 15 years of age with a slight male predisposition [1, 5]. The age of our case does not correspond to the common age of intracranial PNETs, which adds to the importance of our case. Our case was observed in a female patient that did not agree with the predominance of males [1].
Supratentorial cerebral hemispheres are the most common sites of involvement for adult intracranial PNET [1]. The location for PNET of our case was also supratentorial.
The clinical features of intracranial PNETs are diverse. The reported symptoms for adult intracranial PNETs included headache and vomiting (most common symptoms), hemiplegia, muscle strength decrease, facial palsy, deafness and hearing disturbance, drowsiness, fatigue, epilepsy, memory decline, and ataxia [1]. Our case was the first case which manifested as aphasia. The major causes of aphasia are a cerebral vascular accident (stroke) or head trauma. Aphasia can also be the result of brain tumors, brain infections, or neurodegenerative diseases [1].
Adult intracranial PNETs predominantly show mixed isointense to hypointense signals on T1-weighted on MRI images, and isointense to hyperintense signals on T2- weighted on MRI images [1, 5]. The MRI findings in our case were consistent with these findings. For post-contrast MRI, Jiang et al. reported the heterogeneous enhancement of in 6 cases of adult intracranial PNETs, and intense enhancement in 4 cases [1]. Our case showed heterogeneous enhancement.
Histopathological differential diagnosis for intracranial PNETs includes central nervous system (CNS) embryonal tumors (such as medulloblastoma, neuroblastoma, atypical teratoid/rhabdoid tumor), malignant meningioma, lymphoma, rhabdomyosarcoma and melanoma [1, 3]. However, it is necessary to identify PNET correctly and differentiate it from other CNS embryonal tumors due to different treatment and prognosis (PNET requires focal radiotherapy while other CNS embryonal tumors require craniospinal irradiation) [3].
Membranous expression of CD99 is a highly reliable and sensitive, but not specific, diagnostic marker for intracranial PNETs and was detected in almost all patients [1, 3, 5]. Molecular cytogenetics showing EWSR1 gene rearrangement is the golden standard for diagnosis of PNET. Because chromosomal translocations are not unique to this tumor the diagnosis of PNETs can be confirmed based on the comprehensive histopathological, immunohistochemical and molecular cytogenetics examinations [1, 3]. It is noteworthy that CNS embryonal tumors are negative for CD99 and negative for EWSR1 molecular rearrangement [5].
Jiang et al. [1] present a case of intracranial PNET located in the left frontoparietal lobe of a 55-year-old female patient who presented with memory decline and treated by gross total resection (GTR) with adjuvant radiotherapy. In terms of age, symptoms and adjuvant treatment, there are differences between our case and their case, but in terms of tumor location, there is similarity between the two cases.
Chen et al. [2] reported a case of intracranial PNET located in the right parietal lobe of a 43 years old male patient who presented with the chief complaint of epilepsy and treated by GTR with adjuvant chemoradiotherapy; he died after 48 months post operation.
VandenHeuvel et al. [3] reported a case of intracranial PNET located in the right temporal lobe of a 61 years old male patient who presented with left hemiparesis and left-side facial drooping, He underwent just biopsy. In terms of age, tumor location, symptoms and treatment there was no agreement between our case and their case.
A standard treatment plan for intracranial PNETs has not yet been established. Surgical resection (GTR) is the main therapeutic option [1]. Radiotherapy plays a significant role in improving the survival of patients with intracranial PNETs. Chemotherapy can significantly improve the survival rate. GTR with adjuvant radiotherapy and chemotherapy is probably the best treatment plan for these tumors [2, 5].
Intracranial PNETs are aggressive malignancies with a poor prognosis. The overall 5-year survival rate is estimated to be 19.0% [2]. Wide surgical resection margins could significantly reduce local recurrences. GTR is accompanied with better survival than incomplete tumor resection [1]. Early recurrence and old age may not be associated with a good outcome [5].
To conclude, primary intracranial PNETs in patients > 33 years are extremely rare. Because clinical and imaging characteristics, treatment and prognosis of these tumors remain unclear, further reports are necessary to fully understand them.