WBR0206

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Histology, MainCategory::Microbiology, MainCategory::Pathology
Sub Category	SubCategory::Neurology, SubCategory::Infectious Disease
Prompt	[[Prompt::A 45 year old HIV-positive man is brought to the Emergency Room after experiencing gradual blurring in the superior left lateral portion of his vision in both eyes over the past several days. Neurologic exam reveals no other neurologic deficits. A head CT shows a single uniformly enhancing lesion in the right temporal lobe. Which of the following is most likely to be observed on biopsy of this lesion?]]
Answer A	AnswerA::B Cells
Answer A Explanation	AnswerAExp::An example of CNS Lymphoma on MRI is shown below, courtesy of Radiopaedia. Note the solidary subependymal lesion.
Answer B	AnswerB::Toxoplasma Gondii
Answer B Explanation	[[AnswerBExp::Toxoplasma gondii is the primary cause of focal central nervous system disease in AIDS. Distinguishing a primary CN lymphoma vs toxoplasmosis infection ca be difficult. Primary CNS Lymphomas are nearly always a solitary lesion whereas toxoplasmosis typically (86%) displays multiple foci of infection. CNS Lymphoma typically displays a uniform or solid enhancement whereas toxoplasmosis is characterized by ring enhancement. Finally, the patients clinical presentation is not consistent with an infectious etiology; the patient has no fever, constitutional symptoms or epilepsy due to encephalitis. An example of toxoplasmosis on MRI is shown below, courtesy of Radiopaedia. Note the multiple ring-enhancing lesions which fill the basal ganglia.]]
Answer C	AnswerC::Reactive gliosis and formation of new vasculature
Answer C Explanation	AnswerCExp::This is the typical histological appearance of a glial scar.
Answer D	AnswerD::Cryptococcus Neoformans
Answer D Explanation	[[AnswerDExp::Cryptococcus is a common cause of meningitis in HIV patients, however this patient's symptoms are not consistent with meningitis.]]
Answer E	AnswerE::Pseudopalisading tumor
Answer E Explanation	[[AnswerEExp::This is the histologic appearance of a Glioblastoma multiforme (GBM), a highly malignant brain tumor. There is no increased risk of GBMs in HIV patients.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::Primary CNS Lymphoma is a primary intracranial tumor appearing mostly in patients with severe immunosuppression (typically patients with AIDS). A primary CNS lymphoma usually presents with seizure, headache, cranial nerve findings, altered mental status, or other focal neurological deficits typical of a mass effect. In this case, a tumor of the right temporal lobe has disrupted Meyer’s loop causing the visual field defect. Meyer’s loop is a collection of axons from relay neurons in the lateral geniculate nucleus that carry visual information corresponding to the superior lateral visual field to the visual cortex. CNS lymphoma Toxoplasma gondii Educational Objective: Primary CNS lymphomas can affect AIDS patients; they cause focal neurological defects and appear as single, uniformly enhancing masses on MRI. References: First Aid 2014 page 169, First Aid 2012 page 194, 387, Radiopaedia’s excellent article on Primary CNS Lymphoma vs Toxoplasmosis]]
Approved	Approved::Yes
Keyword	WBRKeyword::Brain, WBRKeyword::Cancer, WBRKeyword::Lymphoma, WBRKeyword::Brain tumor, WBRKeyword::Brain imaging, WBRKeyword::HIV, WBRKeyword::AIDS, WBRKeyword::Toxoplasmosis
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