from march 2001 to february 2005 , we performed us in 58 patients , mri in 24 patients , and both mri and us in 10 patients for a total of 72 patients ( 63 women and 9 men , age range : 19 - 70 years , average age : 50 years ) who were clinically suspected of having morton neuroma . by review of the pathologic and surgical reports on the medical records , the final study group of this report was comprised of twenty confirmed morton neuromas in 17 patients among the 72 patients : 12 neuromas ( in 11 patients ) were pathologically confirmed by partial neurectomy ; the remaining eight neuromas ( in 6 patients ) were confirmed by gross inspection at the time of surgery , and these were remedied by neurolysis . all the surgery was performed by one experienced orthopedic surgeon . the surgical decision for surgery was based on the clinical findings and the pre - operative mri and/or us reports . patients were asked to access their satisfaction with the operation results according to the system advocated by johnson et al . ( 14 ) as follows : 1 ) completely satisfied ( essentially pain free , no restrictions in activity and only minor restrictions in footwear ) , 2 ) satisfied with minor reservations ( occasional mild pain , minor restrictions in activity and minor restrictions in foot wear ) , 3 ) satisfied with major reservations ( mild or moderate pain , moderate restrictions in activity and major restrictions in footwear , but overall improvement ) , 4 ) dissatisfied ( no improvement in pain or worse pain , major restrictions in activity and footwear , or worse symptoms ) . the grades of the patients ' satisfaction and the difference of the grades according to the methods of treatment were analyzed . the us evaluation was performed by one of four experienced musculoskeletal radiologists with using 9-mhz linear array transducers ( hdi 5000 , advanced technology laboratories , bothell , wa ) . the us images were obtained from the plantar aspect of the foot in the transverse and longitudinal planes , relative to the metatarsal shafts , with each patient in a sitting position with their feet in slight plantar flexion . the diagnostic criterion for morton neuroma , as assessed by us , was a well - defined , round or ovoid , hypoechoic ( relative to the adjacent muscle ) mass located just proximal to the metatarsal heads in the plantar aspect of the intermetatarsal space ( 5 ) . all the mr imaging studies were performed on a 1.5-t scanner ( signa horizon , ge medical systems , wi ) . the patients were examined in the supine position with the foot placed in plantar flexion within a transmit - receive extremity coil . the imaging protocol consisted of a t1-weighted spin - echo sequence ( t1wi ; tr / te , 550/9 ) , a fast spin echo ( fse ) t2-weighted sequence ( t2wi ; tr / te , 4000/96 ) and a t1-weighted fat - suppressed spin - echo sequence ( contrast - enhanced fat - saturated [ cefs ] t1wi ; tr / te , 617/12 ) that was obtained after the intravenous injection of 0.2 ml / kg gadopentetate ( magnevist , schering , berlin , germany ) . the imaging plane was oblique coronal , and this was perpendicular to the metatarsal bones . the section thickness was 3 - 5 mm without an intersection gap , the image matrix was 256  192 or 256  256 and the field of view was 10 - 14 cm ( mostly 12 cm ) ; this resulted in in - plane resolution of 0.220 - 0.292 mm ( pixel size ) . the diagnostic criterion for mr imaging was a well - demarcated ovoid or dumbbell - shaped intermetatarsal mass at the plantar aspect near the metatarsal heads , and the mass had intermediate to low signal intensity on both t1wi and t2wi ( 1 , 15 , 16 ) . the comparison of the us and mr imaging findings was performed retrospectively by a consensus of two experienced radiologists , and then each image was correlated with the surgical and pathologic findings . the size of the lesion was measured as the largest transverse diameter on both us and mri . the fluid between the metatarsal bones ( the inter - metatarsal bursa ) was excluded during the measurement of the lesion on mri . in addition , we compared the t1wi with the cefs t1wi for lesion conspicuity and for detecting morton neuroma . from march 2001 to february 2005 , we performed us in 58 patients , mri in 24 patients , and both mri and us in 10 patients for a total of 72 patients ( 63 women and 9 men , age range : 19 - 70 years , average age : 50 years ) who were clinically suspected of having morton neuroma . by review of the pathologic and surgical reports on the medical records , the final study group of this report was comprised of twenty confirmed morton neuromas in 17 patients among the 72 patients : 12 neuromas ( in 11 patients ) were pathologically confirmed by partial neurectomy ; the remaining eight neuromas ( in 6 patients ) were confirmed by gross inspection at the time of surgery , and these were remedied by neurolysis . all the surgery was performed by one experienced orthopedic surgeon . the surgical decision for surgery was based on the clinical findings and the pre - operative mri and/or us reports . patients were asked to access their satisfaction with the operation results according to the system advocated by johnson et al . ( 14 ) as follows : 1 ) completely satisfied ( essentially pain free , no restrictions in activity and only minor restrictions in footwear ) , 2 ) satisfied with minor reservations ( occasional mild pain , minor restrictions in activity and minor restrictions in foot wear ) , 3 ) satisfied with major reservations ( mild or moderate pain , moderate restrictions in activity and major restrictions in footwear , but overall improvement ) , 4 ) dissatisfied ( no improvement in pain or worse pain , major restrictions in activity and footwear , or worse symptoms ) . the grades of the patients ' satisfaction and the difference of the grades according to the methods of treatment were analyzed . the us evaluation was performed by one of four experienced musculoskeletal radiologists with using 9-mhz linear array transducers ( hdi 5000 , advanced technology laboratories , bothell , wa ) . the us images were obtained from the plantar aspect of the foot in the transverse and longitudinal planes , relative to the metatarsal shafts , with each patient in a sitting position with their feet in slight plantar flexion . the diagnostic criterion for morton neuroma , as assessed by us , was a well - defined , round or ovoid , hypoechoic ( relative to the adjacent muscle ) mass located just proximal to the metatarsal heads in the plantar aspect of the intermetatarsal space ( 5 ) . all the mr imaging studies were performed on a 1.5-t scanner ( signa horizon , ge medical systems , wi ) . the patients were examined in the supine position with the foot placed in plantar flexion within a transmit - receive extremity coil . the imaging protocol consisted of a t1-weighted spin - echo sequence ( t1wi ; tr / te , 550/9 ) , a fast spin echo ( fse ) t2-weighted sequence ( t2wi ; tr / te , 4000/96 ) and a t1-weighted fat - suppressed spin - echo sequence ( contrast - enhanced fat - saturated [ cefs ] t1wi ; tr / te , 617/12 ) that was obtained after the intravenous injection of 0.2 ml / kg gadopentetate ( magnevist , schering , berlin , germany ) . the imaging plane was oblique coronal , and this was perpendicular to the metatarsal bones . the section thickness was 3 - 5 mm without an intersection gap , the image matrix was 256  192 or 256  256 and the field of view was 10 - 14 cm ( mostly 12 cm ) ; this resulted in in - plane resolution of 0.220 - 0.292 mm ( pixel size ) . the diagnostic criterion for mr imaging was a well - demarcated ovoid or dumbbell - shaped intermetatarsal mass at the plantar aspect near the metatarsal heads , and the mass had intermediate to low signal intensity on both t1wi and t2wi ( 1 , 15 , 16 ) . the comparison of the us and mr imaging findings was performed retrospectively by a consensus of two experienced radiologists , and then each image was correlated with the surgical and pathologic findings . the size of the lesion was measured as the largest transverse diameter on both us and mri . the fluid between the metatarsal bones ( the inter - metatarsal bursa ) was excluded during the measurement of the lesion on mri . in addition , we compared the t1wi with the cefs t1wi for lesion conspicuity and for detecting morton neuroma . among the 20 neuromas ( in 17 patients ) , 12 neuromas ( 12/20 , 60% ) were found in the third intermetatarsal space and the other eight neuromas ( 8/20 , 40% ) were in the second intermetatarsal space ( table 1 ) upon operation . therapeutic success was assessed at the post - operative 2-month follow - up in 13 patients because four patients who underwent excision were unfortunately lost during follow up . eleven out of the 13 patients ( 11/13 , 85% ) had near complete relief from pain , two ( 2/13 , 15% ) had moderate improvement with some remaining pain , and none of the patients became worse . complete relief or marked improvement of the pain was seen in six patients ( 6/7 , 86% ) treated by excision and in five patients ( 5/6 , 83% ) treated by neurolysis ( table 1 ) . among the confirmed 20 morton neuromas ( in 17 patients ) , us was performed for 14 neuromas ( 11 patients ) , mri was performed for 17 neuromas ( 15 patients ) , and both us and mri were performed for 11 neuromas ( 9 patients ) . the typical appearance of morton neuroma on the us and mr images is shown in figure 1 . us depicted 11 out of 14 neuromas correctly , but the remaining three neuromas were not detected . on the other hand , mri detected 13 out of 17 neuromas correctly , but the remaining four neuromas were not detected . hence , the detection rate of mri for morton neuroma was 76% ( 13/17 ) . figure 2 shows the true positive and false negative lesions in the patients who underwent both us and mr imaging . us demonstrated a mass in only the third intermetatarsal space , while the mr imaging revealed a mass in only the second intermetatarsal space . three patients had false negative results on the us imaging analysis , and four patients had false negative results on the mri analysis ( table 1 ) . among them figure 3 shows the case confirmed by excision and pathologically proven , but it was false negative on mr . on us , the mean size of the measured neuromas was 4.9  1.45 mm ( range : 4 - 9 mm ) . on mri , the mean size of the neuroma was 5.1  1.32 mm ( range : 3 - 8 mm ) . most of the neuromas were 5 mm or less ( 10 of the 14 neuromas [ 71% ] detected on us and 10 of the 17 neuromas [ 59% ] detected on mri ) . the maximum difference in size for the same masses measured by us and mr imaging was less than 1 mm . of the 13 neuromas depicted by mr imaging , three were visualized only on t1wi , while one was noted only on the cefs t1wi . accordingly , the neuromas detected on t1wi ( 12/13 , 92% ) outnumbered those on the contrast - enhanced images ( 10/13 , 77% ) ( table 1 ) . among the 20 neuromas ( in 17 patients ) , 12 neuromas ( 12/20 , 60% ) were found in the third intermetatarsal space and the other eight neuromas ( 8/20 , 40% ) were in the second intermetatarsal space ( table 1 ) upon operation . therapeutic success was assessed at the post - operative 2-month follow - up in 13 patients because four patients who underwent excision were unfortunately lost during follow up . eleven out of the 13 patients ( 11/13 , 85% ) had near complete relief from pain , two ( 2/13 , 15% ) had moderate improvement with some remaining pain , and none of the patients became worse . complete relief or marked improvement of the pain was seen in six patients ( 6/7 , 86% ) treated by excision and in five patients ( 5/6 , 83% ) treated by neurolysis ( table 1 ) . among the confirmed 20 morton neuromas ( in 17 patients ) , us was performed for 14 neuromas ( 11 patients ) , mri was performed for 17 neuromas ( 15 patients ) , and both us and mri were performed for 11 neuromas ( 9 patients ) . the typical appearance of morton neuroma on the us and mr images is shown in figure 1 . us depicted 11 out of 14 neuromas correctly , but the remaining three neuromas were not detected . hence , the detection rate of us was 79% ( 11/14 ) . on the other hand , mri detected 13 out of 17 neuromas correctly , but the remaining four neuromas were not detected . hence , the detection rate of mri for morton neuroma was 76% ( 13/17 ) . figure 2 shows the true positive and false negative lesions in the patients who underwent both us and mr imaging . us demonstrated a mass in only the third intermetatarsal space , while the mr imaging revealed a mass in only the second intermetatarsal space . three patients had false negative results on the us imaging analysis , and four patients had false negative results on the mri analysis ( table 1 ) . among them , five patients underwent neurolysis and only one patient underwent excision . figure 3 shows the case confirmed by excision and pathologically proven , but it was false negative on mr . on us , the mean size of the measured neuromas was 4.9  1.45 mm ( range : 4 - 9 mm ) . on mri , the mean size of the neuroma was 5.1  1.32 mm ( range : 3 - 8 mm ) . most of the neuromas were 5 mm or less ( 10 of the 14 neuromas [ 71% ] detected on us and 10 of the 17 neuromas [ 59% ] detected on mri ) . the maximum difference in size for the same masses measured by us and mr imaging was less than 1 mm . of the 13 neuromas depicted by mr imaging , three were visualized only on t1wi , while one was noted only on the cefs t1wi . accordingly , the neuromas detected on t1wi ( 12/13 , 92% ) outnumbered those on the contrast - enhanced images ( 10/13 , 77% ) ( table 1 ) . morton neuroma was first described by thomas morton in 1876 as " a peculiar and painful affection of the fourth metatarsophalangeal articulation " ( 17 ) . however , subsequent studies have shown that the third and second spaces are the more common sites for neuroma ( 5 ) . our study has also demonstrated that the third space is the most common site of involvement . it is generally accepted that the development of morton neuroma may be induced by repetitive compression of the plantar nerve against the deep transverse intermetatarsal ligament , with subsequent perineural fibrosis ( 18 ) . a tentative diagnosis of morton neuroma can be made at the time of clinical assessment , but imaging correlation is required for the exact localization of neuroma and for the detection of multiple lesions , and especially when the clinical findings are indeterminate . this can prevent patients from undergoing rather avoidable surgical exploration at the wrong sites , which may lead to inadvertent complications ( 5 , 17 ) . in addition , other causes of metatarsalgia can also be excluded via imaging modalities . the possible clinical differential diagnoses that can cause metatarsalgia include intermetatarsal bursitis , stress fractures , necrosis of the sesamoid bones , synovitis of the metatarsophalangeal joint , infection and true neoplasm ( 3 , 8) . these include intermetatarsal bursitis , ganglion cyst , synovial cyst , giant cell tumor ( gct ) of the adjacent tendon sheath , fibromatosis , nodular fasciitis , pigmented villonodular synovitis and physiologic fluid distention of the intermetatarsal bursa when examining by using us and mri ( 4 , 17 ) . an investigation using us suggested that if a mass in the interdigital space is greater than 20 mm in length , then it is an abnormality other than neuroma such as a ganglion cyst , a synovial cyst or a gct of the adjacent tendon sheath ( 17 ) . several sonographic study results have disclosed a prospective sensitivity of 95 - 98% for morton neuromas and a retrospective sensitivity of up to 100% ( 5 , 6 , 9 ) . however , a recent study by quinn et al . ( 17 ) revealed that 85% of neuromas with an average width of 6 mm , an average height of 9 mm and an average length of 13 mm were identified prospectively . analysis by us in our study showed a relatively low detection rate ( 79% ) of morton neuroma . sonography is a very operator - dependent technique , for instance , the sonographer 's experience is quite important , and so erroneous detection does factor into us examinations . the size of the morton neuroma is considered as another factor contributing to the variability of detection . the diameter of the normal plantar digital nerve is 1 - 2 mm at the level of the intermetatarsal heads and the normal nerve is not readily identifiable on sonography ( 5 , 9 ) . in our study , the mean sizes of the masses were 4.9 mm with using us and 5.1 mm with using mri , and these values were smaller than those reported in a previous study ( 6.5 mm for us and 7.4 mm for mri ) ( 11 ) . mr imaging is a highly sensitive modality ( 87% ) for the detection of morton neuroma ( 1 ) . our mr imaging evaluation ( detection rate : 76% ) did not show a better detection result than that expected at the beginning of the study . two neuromas were as small as 4 mm in transverse diameter ( one of these is the case presented in figure 2 ) . that these lesions were missed was possibly due to their smaller size , and it was possibly due to the surgeon 's subjective diagnosis in the cases of surgical neurolysis in our study . we should again consider the matter of the lesions ' size . in our study , most of the neuromas that were operated upon were 5 mm or less . there was no lesion less than 3 mm detected by either the us or mri modalities . in this aspect , the size of the lesions that were operated in our study was relatively smaller as compared with previous studies ( 1 , 3 , 7 , 17 ) . the measurement of morton neuroma on the transverse mr image is dependent on the placement of the foot in the scanner . in addition , the size of the morton neuroma is significantly larger in the prone position with plantar flexion of the ankle than in the supine and upright weight - bearing positions , in which the ankle is dorsiflexed ( 15 ) . our study was done with the foot placed in the supine position , which possibly caused a decreased diameter of the neuroma , although plantar flexion was applied to the ankle . the transverse diameter can be affected by the patient 's position or by the compression pressure during sonography . previous studies have demonstrated that neuromas larger than 5 mm in diameter are more symptomatic than the smaller ones ( 3 , 5 , 6 ) . ( 7 ) showed that a more favorable clinical outcome can be expected after surgical intermetatarsal neurectomy when a morton neuroma has a transverse measurement larger than 5 mm on mri scans ; 77% of the patients in that study had a good outcome when the neuroma was greater than 5 mm , compared with only 17% of the patients had a good outcome when their neuromas measured 5 mm or less . ( 11 ) demonstrated that symptoms were not dependent on the size of the neuroma . moreover , the mr imaging diagnosis of morton neuroma does not always imply symptomatology ; thus , careful correlation between the clinical and mr imaging findings is mandatory ( 4 ) . the fluid distention of the intermetatarsal bursa may mimic that of neuromas , but it may not manifest symptoms and it is typically less than 3 mm in transverse dimension ( 3 ) . there are different opinions regarding the best mr imaging sequences for detecting morton neuroma ( 12 , 15 , 16 ) . erickson et al . ( 16 ) reported that t1wi was the most useful sequence because neuromas with decreased signal intensity were well demarcated from the adjacent fat tissue . on the other hand , zanetti et al . ( 3 ) suggested that t2wi was beneficial in order to exclude other diseases that mimic neuroma , such as intermetatarsal bursitis , because the latter revealed high signal intensities . terk et al . ( 12 ) stressed that sequences with fat - suppression and contrast - enhancement were reliable sequences for showing high - contrast images , and their study revealed that t1wi alone failed to demonstrate the presence of 50% ( 3 of 6 ) of the neuromas . in our study , the t1wi revealed better results for the detection of morton neuroma than the cefs t1wi did . in particular , the rarely enhanced neuroma cases shown in figures 1 and 3 were better discriminated on t1wi than on cefs t1wi . however , the opposite was also true in figure 2 when the neuroma was well enhanced . we think that cefs t2wi is not obligatory for the purpose of detection alone , although it can be necessary for differentiation of neuroma from other possible lesions . the falsepositive and true - negative rates could not be obtained because our study group consisted of only surgically proven morton neuromas ( including cases of neurolysis that might have been related to the surgeon 's subjectivity ) . in addition , performing surgical exploration in the asymptomatic intermetatarsal spaces in clinical settings is not ethically possible whether or not a suspected morton neuroma is found on imaging studies . the second limitation is the retrospective analysis of the us findings , is that , sonography is an operator - dependent method . the third limitation is that the double lesions in one patient were not separately evaluated in the clinical outcome . in summary , us and mr imaging are compatible modalities for the evaluation of morton neuroma , and both modalities have relatively high detection rates . both imaging studies can provide information on the location and size of the neuroma prior to surgery . in addition , the contrast enhanced sequence does not seem essential for the detection of neuroma .