Table 1.

Differences between primary, secondary CNS lymphomas, and primary dural lymphomas

	PCNSL	SCNSL	PDL
Types	90% of intracranial lymphomas are aggressive, most commonly DLBCL 10% of all dural lymphomas are low‐grade lymphomas, lymphoblastic, T‐cell, Burkitt's lymphomas, and intraparenchymal marginal zone lymphoma	Involves leptomeninges (60% of cases), the brain parenchyma, and few cases involve the eyes	It is a rare subtype of PCNSL Originates in the dura matter and can involve the epidural or subdural space. Does not affect the brain parenchyma
Incidence	Represents 2% of primary CNS tumors in the United States 30 Annual incidence in the US is approximately 1400 new cases each year 30	Occurs in <1% of indolent and <5% of aggressive systemic lymphomas when CNS prophylaxis is given 32 May occur in up to 50% of cases of Burkitt's/lymphoblastic lymphoma or AIDS‐related lymphoma when no prophylaxis is given 32	Unknown. There are only case reports/case series published
Diagnosis	On imaging, solitary mass is seen in 70% of cases, commonly in the supratentorial region, with a tendency to affect the periventricular white matter In immune‐suppressed patients, multiple lesions are seen twice as often	Neither MRI nor histology itself is able to distinguish between PCNSL and SCNSL. Systemic lymphoma must be excluded in the case of all histologically proven brain lymphoma lesions	Either a single or multiple extra‐axial lesions that are diffusely enhancing are seen on imaging. 95% of images revealed a dural tail
Characteristics	Immunocompetent patients with DLBCL have secondary involvement of the CNS in 1%‐10% of the cases	Extranodal lymphoma, especially involvement of the kidneys and/or adrenal glands, testes, and female reproductive tract, as well as extensive marrow involvement, has been demonstrated to be a site‐specific additional risk factor for SCNSL	More common in women Symptoms are nonspecific: headaches, meningeal irritation, seizures or epilepsy, scalp swelling, and symptoms of cranial nerve involvement
IHC staining	Most PCNS DLBCL express CD19, CD20, and CD79a antigens. 10% ‐ 20% are CD10+, and 50% ‐ 80% are BCL6 and BCL2 positive 95% stain positive for MUM‐1 PCNSL shows somatic hypermutation of genes such as BCL6, MYC, PIM1, and PAX5 31	Unclear	Immunological staining is generally positive for CD20, CD22, CD19 and CD79a and PAX‐5. Tumor cells are positive for BCL2 50% of cases are CD43 positive
Treatment	High‐dose methotrexate (MTX)‐based induction chemotherapy combined with other chemotherapeutic agents It is known to be radiosensitive	High‐dose chemotherapy with autologous stem cell transplant is feasible and effective Two or more cycles of induction chemotherapy (high‐dose MTX and/or cytarabine) oral targeted therapies or therapies such as rituximab have shown promising results	Most patients undergo surgical treatment, radiotherapy or chemotherapy; or a combination thereof. >50% patients undergo surgical resection. In single site disease, surgery + focal relatively low‐dose radiotherapy In systemic disease, R‐CHOP + maintenance Rituximab
Prognosis	Aggressive behavior and overall poor outcome	Very poor prognosis	Indolent disease with a good prognosis PDLs have a 5‐year overall survival rate is >86%