LAUSR

OBJECTIVE The diagnosis of peripheral neurolymphomatosis (NL) is difficult and often delayed, since patients can have isolated, non-specific nerve symptoms. Magnetic resonance imaging usually shows non-specific findings of enlarged, contrast-enhancing nerves. We aim to elucidate the mechanism behind an imaging finding that we believe is pathognomonic of this disease and likely of other hematologic diseases with peripheral nerve involvement. METHODS We reviewed imaging studies of a previously published cohort of patients, in addition to more recent patients, all with tumefactive NL where enlarged nerve bundles are surrounded by tumor. We reviewed demographics, clinical data (primary or secondary disease, biopsy-proven diagnosis), and imaging findings (tumefactive appearance, primary involved nerve, location of epicenter of tumefactive appearance, vascular involvement). RESULTS All cases showed a maximum tumefactive appearance at branch or junction points with a gradual decrease of this appearance moving proximally and distally from the epicenter in a "crescendo-decrescendo" pattern. We describe this as a phasic mechanism with three phases: malignant cells fill the intraneural space, extrude at a weak spot of the nerve which often occurs at a branch or junction point, and then expand and fill the subparaneurial space creating the grossly tumefactive appearance with proximal and distal spread. CONCLUSION We present a novel, unifying theory explaining the pathognomonic tumefactive appearance of NL. Our theory offers the first rational explanation for the radiological appearance of this disease with peripheral nerve involvement. We believe that with earlier recognition of this disease on imaging, patients can receive a faster diagnosis and earlier treatment.