Post-transplant lymphoproliferative disorder (PTLD)

Lateral ventricular hydrocephalus with effacement of the supratentorial sulci. A mass is centered on the septum pellucidum, presumably obstructing outflow through the foramen of Monro. 

Centered upon the septum pellucidum just above the foramen of Monro, which it obstructs, is and a peripherally enhancing mass with central non-enhancement. The enhancing component demonstrates intermediate diffusion restriction (1000-1200 x 10^-6 mm^2/s) with facilitated diffusion centrally. MR spectroscopy demonstrates some elevation of choline and a lipid/lactate peak. Cerebral blood volume appears somewhat elevated in the enhancing component of the mass. Enhancement appears to creeping up the septum pellucidum superiorly. Edema is seen primarily inferior to the mass outlining the anterior commissure and the columns of the fornices which are involved by the mass. It is an isolated focus of the abnormality, with no other ventricular or leptomeningeal areas of abnormal enhancement. The remainder of the brain in the posterior fossa content are unremarkable. Normal flow voids are seen. The lateral ventricles are enlarged with transependymal edema consistent with obstruction at the level of the foramen of Monro.

Conclusion: Mass in the septum pellucidum with resultant obstructive hydrocephalus. The lesion is unusual and a number of entities should be considered. The classic lesion to arise from the septum pellucidum is a central neurocytoma, and although this should be considered, imaging features are quite atypical is thought unlikely to represent this entity. A more likely diagnosis is that of a pilocytic astrocytoma, or a high-grade glial tumor (anaplastic oligodendroglioma, anaplastic astrocytoma, glioblastoma). Lymphoma is another possibility and although the appearance is a little atypical, in the setting of immunosuppression (renal transplant) this remains a very viable diagnosis along with post-transplant lymphoproliferative disorder (PTLD). 

The patient went on to have a biopsy. 

Histology

Sections of brain tissue show a dense infiltrate composed of predominantly small lymphocytes, histiocytes and scattered individual and small clusters of atypical lymphoid cells. The large atypical cells demonstrate frequent binucleation with prominent nucleoli and voluminous pale eosinophilic cytoplasm with perinuclear clearing and vacuolation.

Immunohistochemical results indicate the large atypical cells stain as follows:

• CD20 patchy positive
• CD30 strong positive
• EBER-CISH positive
• OCT2 positive
• PAX5 weak positive
• BOB1 weak positive
• CD79a weak positive
• MUM1equivocal
• CD45 negative

The background small lymphocytes show a mixed population on CD3+ T-cells and CD20+ B-cells, together with aggregates CD68+ histiocytes.

Comment: The presence of Reed-Sternberg-like cells with a compatible immunophenotype favors a diagnosis of classical Hodgkin lymphoma occurring in the setting of previous solid-organ transplantation. Other forms of post-transplant lymphoproliferative disorders (PTLD), such as the polymorphic variant, are considered less likely. There are no features to indicate a monomorphic variant of PTLD.

FINAL DIAGNOSIS: Classical Hodgkin lymphoma-like post-transplant lymphoproliferative disorder (PTLD).