ObjectiveTo explore the value of ¹⁸F-FDG PET/CT examination in the differential diagnosis of primary nasopharyngeal lymphoma (PNL) and nasopharyngeal carcinoma (NPC).

MethodsPET/CT data of 33 patients with PNL and 71 patients with NPC who were confirmed histopathologically and had not undergone oncotherapy before examination were retrospectively analyzed. The form, range, invasion, volume, SUV_max of nasopharyngeal lesion, and lymphadenopathy involvement were analyzed comparatively. The SUV_max and volume of lesions that confirmed diffuse large B cell lymphoma(DLBCL) were compared with NPC. t-text and χ²-text with SPSS 13.0.

ResultsDiffuse infiltration of all nasopharyngeal walls was detected in 20 of 33 patients with PNL(bilateral symmetry in 14 patients and asymmetry in 6) and 10 of 71 patients with NPC(bilateral symmetry in 4 patients and asymmetry in 6). Partial infiltration of nasopharyngeal walls was observed in 13 of 33 patients with PNL(unilateral invasion in 7 patients and bilateral invasion in 6) and 61 of 71 patients with NPC(unilateral invasion in 39 patients and bilateral invasion in 22). Statistical significances were found between diffuse and partial infiltration, unilateral and bilateral invasion, and symmetry and asymmetry of nasopharyngeal walls of PNL and NPC(χ²=23.75, 10.38, and 16.74, respectively; all P < 0.001). Tumor limited to the nasopharyngeal wall was found in 26 patients with PNL and 17 patients with NPC. Meanwhile, deep-structure invasion was detected in 7 patients with PNL and 54 patients with NPC. Significant difference was found in tumor invasion between PNL and NPC(χ²=27.94; P < 0.001). Tumor volumes of PNL, DLBCL, and NPC were 3.70±5.53×10⁴, 5.05±6.89×10⁴, and 2.06±2.31×10⁴ mm³, respectively. No significant difference was found between tumor volume of PNL and DLBCL compared with NPC(t=1.63 and 1.85 respectively; both P>0.05). The SUV_max's of PNL and NPC were 12.00±6.34, 14.26±6.42, and 10.09±4.41, respectively. No significant difference was found between the SUV_max's of PNL and NPC(t=1.55; P>0.05). Significant difference was found between DLBCL and NPC(t=2.67; P < 0.05). Lesions in 21 patients with PNL and 24 patients with NPC protruded into posterior nasal apertures, and significant difference was found between the two groups(χ²=8.17; P < 0.05). A total of 26 patients with PNL had retropharyngeal or cervical lymphatic involvement. A total of 51 patients with NPC had retropharyngeal or cervical lymphatic metastasis. SUV_max, major diameter, minor diameter, and average diameter did not significantly differ from largest lymphatic involvement or metastasis in PNL and NPC(t=0.79, 1.37, 2.03, and 1.71, respectively; all P>0.05). Through CT imaging, lymphatic necrosis was detected in 3 of 26 patients with lymphatic involvement of PNL and 31 of 51 patients with lymphatic metastasis of NPC. Significant difference was found between the two groups(χ²=16.94; P < 0.001). Lymphatic blend was detected in 5 patients with PNL and in 6 patients with NPC. No significant difference was found between the two groups(χ²=0.78; P>0.05).

ConclusionsPET/CT examination has a definite diagnosis value in patients with PNL and NPC. The differential diagnosis between PNL and NPC was mainly according to form, range, and invasion of nasopharyngeal lesion. The metabolic level of different pathological subtypes may be higher or lower than that of NPC. The metabolic activity of DLBCL was higher than that of NPC. The volume of nasopharyngeal lesion cannot be considered as a main basis to distinguish between PNL and NPC.