|Year : 2006 | Volume
| Issue : 1 | Page : 18-22
Diagnostic Utility and Clinical Significance of Three Phase Bone Scan in Symptomatic Accessory Navicular Bone
Pushpalatha Sudhakar, Anshu Rajneesh Sharma, G Narsimhulu, VVS Prabhakar
Nizamís Institute of Medical Sciences, Hyderabad, Andhra Pradesh, India
Department of Nuclear Medicine, Nizamís Institute of Medical Sciences, Punjagutta, Hyderabad - 500082
Source of Support: None, Conflict of Interest: None
| Abstract|| |
More than one center of ossification is frequently found in asymptomatic children and adolescents and is regarded as a normal variant. Accessory navicular bone is one of the supernumerary ossicles in the foot. It may present incidentally or may be present with clinical manifestations. Radiograph is non diagnostic in symptomatic cases. 99mTc MDP bone scan shows focal intense uptake. Advantage of three phase bone scan over single delayed skeletal phase in the diagnosis of symptomatic accessory naviculars and it's clinical significance in foot pain was retrospectively analyzed in ten cases of accessory naviculars (five unilateral and five bilateral) in the present study. Bone scans were correlated with radiographs. Intense hyperemia in initial phase and focal intense uptake in delayed phase was taken as characteristic feature for symptomatic accessory navicular. All the symptomatic accessory naviculars (100%) showed positive three phases. Only two out of eleven asymptomatic accessory naviculars (18%) showed positive hyperemia in the initial phase whereas rest showed absence hyperemia. Our study concluded that additional vascular & bloodpool phases improve sensitivity and specificity in diagnosing symptomatic accessory navicular as the main cause of foot pain.
Keywords: Three phase bone scan, symptomatic accessory navicular, Hyperemia.
|How to cite this article:|
Sudhakar P, Sharma AR, Narsimhulu G, Prabhakar V. Diagnostic Utility and Clinical Significance of Three Phase Bone Scan in Symptomatic Accessory Navicular Bone. Indian J Nucl Med 2006;21:18-22
|How to cite this URL:|
Sudhakar P, Sharma AR, Narsimhulu G, Prabhakar V. Diagnostic Utility and Clinical Significance of Three Phase Bone Scan in Symptomatic Accessory Navicular Bone. Indian J Nucl Med [serial online] 2006 [cited 2019 Aug 24];21:18-22. Available from: http://www.ijnm.in/text.asp?2006/21/1/18/43435
| Introduction|| |
The accessory navicular bone (ANB) (Os tibialis externum or navicular secundrium) is one of the several supernumerary ossicles of foot with 6% to 12% incidence  . There is a strong female predominance and may be bilateral in 50% to 90% of cases. 
Accessory ossicles are commonly mistaken for fractures. Accessory navicular has been reported as cause of foot pain and is usually associated with flat foot 3. Plain radiographic identification of accessory navicular is insufficient to attribute symptomatology. Increased radio tracer uptake on bone scan is found to be more sensitive. MRI is of high diagnostic value for demonstrating both bone marrow changes and soft tissue edema.
Clinical relevance of positive bone scan in symptomatic Accessory navicular had been discussed in previous literature. It was shown that bone scan has high sensitivity but positive findings lack specificity  . The significance of three phase bone scans instead of a single delayed scan in the evaluation of symptomatic ANB has been discussed in the present study.
| Materials and Methods|| |
The study group includes ten patients in whom(ANB)has been diagnosed on bone scan and confirmed by plain radiograph later on. One patient presented with radiographic diagnosis of accessory navicular in which bone scan was normal. The demography of study population is given in [Table 1].
Nine patients were referred from Rheumatology and/or Orthopedic departments with clinical diagnosis of inflammatory arthritis or stress fracture, presenting with or without foot pain. Only one patient out of nine presented with radiographically diagnosed ANB where as rest off all detected to have accessory navicular following bone scan. One patient was referred from oncology department for metastatic work up in which Accessory navicular was diagnosed incidentally.
Three phase bone scan was performed using dual Head Gamma Camera (Seimen's, E Cam). Initial blood pool phase was acquired at 5minutes post injection of 740 MBq of Tc99m MDP. Delayed skeletal phase was acquired at 3hrs. Spot images of anterior & posterior feet and plantar views were acquired in both phases.
Bone scan findings of focal intense osseous radionuclide uptake in the medial aspect of Navicular bone is the diagnostic feature of accessory navicular bone. Blood pool phase and delayed phase were analyzed for the presence of hyperemia and the pattern & intensity of uptake respectively in all patients. Findings of three phase bone scan and its concordance with the symptomatic and asymptomatic clinical features were analyzed retrospectively.
| Results|| |
Five unilateral and five bilateral Accessory naviculars were diagnosed in ten patients. Out of fifteen accessory navicular bones two were negative on bone scan in which the plain radiograph diagnosed their presence. Bone scan findings were assessed in each accessory navicular and were correlated with clinical symptoms. [Table 2] & [Table 3].
Out of five unilateral cases, two were symptomatic clinically. Both presented with clinical diagnosis of metatarsal / tarsal stress fractures. These two showed positive hyperemia in the initial blood pool phase and focal intense osseous uptake in the skeletal phase in the region of accessory navicular on three-phase bone scan [Figure 1]. Out of three asymptomatic cases one was negative in all three phases, in which plain radiograph showed the presence of accessory navicular [Figure 2]. Blood pool phase was negative in the remaining two asymptomatic cases, which showed positive delayed skeletal phase only.
In five cases of B/L Accessory naviculars, three were asymptomatic clinically on both sides. One of these patients showed positive three phases on one side [Figure 3]. The other accessory navicular in the same patient was negative even on delayed phase (rudimentary on radiograph). The remaining two cases showed focal uptake in delayed phase only with absent initial hyperemia [Figure 4]. One of these came for metastatic workup in which incidentally diagnosed B/L Accessory naviculars showed relatively less uptake than adjacent tarsal bone uptake.
Two patients of bilateral accessory naviculars were symptomatic on one side and asymptomatic on the other side. Symptomatic accessory naviculars showed positive hyperemia and delayed osseous uptake on three-phase bone scan [Figure 5]. However even one of the asymptomatic ossicle also showed positive hyperemia.
| Discussion|| |
Accessory navicular bone is one of the supernumerary ossicles of foot found on the medial side,proximal to the navicular and in continuity with tibialis posterior tendon. It represents one of the navicular bone's two growth centers (or ossification centers), the part of each bone that hardens from cartilage in childhood. The patients having flattened than normal feet (flat foot) are more prone  .
Three distinct types of Accessory Naviculars are known  . Type 1 accessory navicular is a sesmoid bone in posterior tibial tendon, accounting for 30% of cases. Type 2 is an accessory ossification center in the tubercle of the navicular bone accounting for 70% of cases. Cornuate navicular is an anomaly related to the presence of osseous bridge connecting the navicular bone and the accessory navicular. Of these three patterns type 2 and cornuate navicular are associated with clinical manifestations particularly pain which is usually evident in second decade of life. When a large portion of the posterior tibial tendon inserts onto either a type 2 and 3 accessory navicular ossicle, the posterior tibial tendon is displaced resulting in a valgus deviated foot, putting the patient at risk of the development of pes planus deformity  .
Accessory navicular is usually present as anatomical and radiological variant. But some times it may be the source of foot pain. The differential diagnosis for symptomatic accessory navicular is tarsal stress fractures, arthritis, and posterior tibial tendon rupture  . If an accessory navicular is present but is unclear whether it is causing symptoms or not, then a radionuclide bone scan is indicated.
The mechanism of pain in accessory navicular has been attributed to traumatic or degenerative changes at the synchondrosis or to soft tissue inflammation when fused  . Histopathology reveals inflammatory chondro osseous changes compatible with chronic stress related injury  . For pain that results from excessive pull of the posterior tibial tendon, cast immobilization will frequently resolve the symptoms. Surgical treatment of painful accessory navicular consists of excision along with its synchondrosis.
All symptomatic accessory naviculars (2 unilateral and symptomatic sides of two B/L accessory navicular cases) showed positive hyperemia in the initial blood pool phase and positive tracer uptake in delayed skeletal phase in our study.
Vigorous and continuous stress on pre existing accessory navicular may traumatize the ossicle producing foot pain. More often this type of clinical presentation is seen in Athletes  . Clinically it may be mistaken for tarsal fracture. Bone scan helps in identifying accessory navicular as the cause of foot pain  . Continuous brisk walk might have resulted in trauma to the accessory navicular producing symptoms in two symptomatic unilateral cases in our study. These two came with clinical suspicion of tarsal stress fracture with background of brisk morning walk habit. One of the B/L accessory navicular cases had H/O trauma with posttraumatic arthritis, in which direct trauma to the accessory navicular would be the cause of pain. In all these cases three phase bone was found to be diagnostic ruling out other causes of foot pain. As compared to previous literature, additional blood pool phase helped in identifying symptomatic osscile in our study improving sensitivity and specificity of bone scan. As shown in earlier studies plain radiograph was not contributory in differentiating symptomatic from asymptomatic accessory naviculars in our study.
Usually in patients with B/L accessory naviculars and unilateral pain, increased uptake lateralizes to symptomatic side. However in our study even the asymptomatic accessory naviculars also showed tracer uptake. It is postulated that positive findings may precede by months and years the onset of symptoms  . In one patient Positive three phase bone scan was seen in asymptomatic accessory navicular. Patient had inflammatory arthritis and showed tenderness over ANB clinically. Pain in the adjacent inflammatory joints might have suppressed the symptoms in accessory naviculars.
Tracer uptake in rest of the asymptomatic cases was found to be either equivalent to the adjacent tarsal bones or mildly increased with out any evidence of hyperemia in the initial blood phase.
Bone scan was negative in all three phases in two cases (one unilateral and one side of one B/L accessory naviculars). Both of them were asymptomatic clinically. Radiograph diagnosed the presence of accessory naviculars. The ossicle is very rudimentary in B/L ANB case. The possibility of occurrence of symptoms in future is minimal in these cases, unless they are traumatized.
In conclusion, the three phase bone scan has helped in diagnosing accessory navicular as cause of foot pain in all symptomatic cases ruling out other possibilities. Our study showed that addition of blood pool phase increases the sensitivity of diagnosing symptomatic accessory naviculars. If the uptake in accessory navicular is equivalent to adjacent tarsals and if there is no hyperemia in the initial phase, frequently they are of asymptomatic incidentally diagnosed ossicles. If asymptomatic accessory naviculars show positive three phase bone scan, it may be taken as predicting factor for future symptoms. These ossicles are more prone for inflammatory changes with repetitive trauma.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]