Labyrinthitis With Negative MRI As a Precursor to Rapidly Developing Primary CNS Lymphoma of the Cerebellopontine Angle

Background

Few case reports have described primary central nervous system lymphoma (PCNSL) presenting as a cerebellopontine angle (CPA) lesion in HIV-positive patients. We describe a rare presentation of rapidly progressing PCNSL of the CPA/internal auditory canal (IAC) as labyrinthitis with initial negative MRI in an HIV-positive patient.

Case

A 58-year-old male with well-controlled HIV presented with sudden left sensorineural hearing loss, tinnitus, and imbalance. Vestibular testing suggested an uncompensated left peripheral vestibular weakness. MRI demonstrated facial and cochleovestibular nerve enhancement within the CPA and IAC. The presumptive diagnosis of labyrinthitis was made. Two months later, he presented to his infectious disease provider with left facial weakness and disequilibrium and was treated for presumed Bell's palsy. One month later, he presented with left corneal reflex dysfunction, decreased visual acuity, diplopia, and worsening ataxia. Repeat MRI demonstrated a new 3.6 cm lesion of the left CPA/IAC with vasogenic edema. Despite location, the mass lacked the brainstem compression characteristic of other extra-axial CPA masses such as vestibular schwannoma. Flow cytometry and cytology from cerebrospinal fluid was consistent with primary central nervous system large B-cell lymphoma.

Conclusions

We present a unique case of rapidly progressing PCNSL of the CPA/IAC in an HIV-positive patient, presenting initially as labyrinthitis with negative MRI followed by development of multiple cranial neuropathies and 3-month repeat MRI demonstrating a large CPA mass. In HIV-positive patients with a similar initial presentation, PCNSL should considered early in the diagnostic evaluation with close clinical monitoring and a low threshold for repeat imaging.

Insight into the Etiology of Undifferentiated Soft Tissue Sarcomas from a Novel Mouse Model

Aberrant activation of the Hedgehog signaling pathway has been linked to the formation of numerous cancer types, including the myogenic soft tissue sarcoma, embryonal rhabdomyosarcoma (eRMS). Here, we report PCG2, a novel mouse model in which human GLI2A, a constitutive activator of Hedgehog signaling, induced undifferentiated sarcomas that were phenotypically divergent from eRMS. Rather, sarcomas arising in PCG2 mice featured some characteristics that were reminiscent of Ewing sarcoma. Even though it is widely understood that Ewing sarcoma formation is driven by EWS-ETS gene fusions, a genetically defined mouse model is not well-established. While EWS-ETS gene fusions were not present in PCG2 sarcomas, precluding their designation as Ewing sarcoma, we did find that GLI2A induced expression of known EWS-ETS gene targets essential to Ewing pathogenesis, most notably, Nkx2.2. Moreover, we found that naïve mesenchymal progenitors originate tumors in PCG2 mice. Altogether, our work provides a novel genetic mouse model, which directly connects oncogenic Hedgehog activity to the etiology of undifferentiated soft tissue sarcomas for the first time. IMPLICATIONS: The finding that activation of Gli2 transcription factor is sufficient to induce Ewing-like sarcomas provides a direct transformative role of the Hedgehog signaling pathway in undifferentiated soft tissue sarcoma.