CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah

Quiescent and Accessory Navicular Syndrome in the same patient Incremental value of bone SPECT-CT of an accessory navicular bone

Introduction

Accessory navicular bone (ANB) results from developmental variation resulting in secondary ossification centers adjacent to the primary navicular bone. ANB is considered a normal variant and is reported to be present in 4-20% of the general population. 1 This accessory ossicle may appear not worth mentioning, however, due to its unique anatomical position in the foot and the biomechanics of gait it can cause significant pain, morbidity and even deformity leading to flat foot. It is inappropriately diagnosed when evaluating foot pain and often confused with an ankle sprain. Tibialis posterior is a large muscle that assists in plantar flexion of the foot and ankle and locks the tarsal bones during gait. Tibialis posterior tendon has multiple insertions in the foot with the most significant on the medial navicular bone. In advanced cases of symptomatic ANB, damage to the tibialis posterior tendon can occur.

Three distinct types of accessory naviculars are known in the literature. Type 1 accessory navicular is a sesamoid bone in posterior tibial tendon. It accounts for 30% of cases. Type 2 is an accessory ossification center in the tubercle of the navicular bone which accounts for 70% of cases. Cornuate navicular is an anomaly related to the presence of an osseous bridge connecting the navicular bone and the accessory navicular. Type 2 and cornuate navicular are mostly symptomatic and associated with clinical manifestations particularly pain.

What Is Accessory Navicular Syndrome?

People who have an accessory navicular often are unaware of the condition if it causes no problems. However, some people with this extra bone develop a painful condition known as accessory navicular syndrome when the bone and/or posterior tibial tendon are aggravated. This can result from any of the following:

Trauma, as in a foot or ankle sprain Chronic irritation from shoes or other footwear rubbing against the extra bone Excessive activity or overuse

Many people with accessory navicular syndrome also have flat feet (fallen arches). Having a flat foot puts more strain on the posterior tibial tendon, which can produce inflammation or irritation of the accessory navicular.

Signs and symptoms of accessory navicular may appear during adolescence, when the bones are maturing, and the growth cartilage is developing into bone. However, sometimes symptoms do not occur until adulthood. Signs and symptoms of accessory navicular syndrome include: a visible bony prominence on the inner side of the foot, local hyperemia, swelling, and vague bone pain, usually occurring during or after activity periods. Diagnosis is commonly suggested by medical history and painful sensitivity within the area of the head of the navicular bone.

Radiological examination is needed to allow the surgeon to visualize the accessory navicular. If there is ongoing pain or inflammation, an MRI or other advanced imaging tests may be used to further evaluate the condition.

CASE

19 years old female patient who complained of pain in the medial area of left foot for 2 years, and the pain getting worse in the last 2 weeks.

X rays’ foot- Plain X-ray did not reveal any abnormality

Referred for the 99mTc MDP BONE SPECT CT SCINTIGRAPHY OF THE FOOT

99mTc MDP SPECT CT IMAGES OF FOOT

CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah 01 CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah 02 CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah 03 CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah 04

Computed tomography (CT) images show a small bony structure medial to navicular bone on both sides with sclerosis (Type II- well-formed accessory navicular bones, which are forming a pseudo joint).

CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah 05 CASE OF THE WEEK – “Quiescent and Accessory Navicular Syndrome in the same patient” by Dr Shekhar Shikare, HOD & Consultant, Nuclear Medicine, NMC Royal Hospital Sharjah 06

Hybrid Bone SPECT/CT fused images show focally increased MDP tracer uptake tracer uptakes in the adjoining region of Type II accessory navicular bones & navicular bone of the LEFT FOOT favoring accessory navicular syndrome.

While in asymptomatic RIGHT FOOT, there is minimal to mildly increased tracer uptakes in the adjoining region of Type II accessory navicular bones & navicular bone favoring quiescent pattern.

The indication 99mTc MDP bone scan is to see if the accessory navicular bone is the cause of symptoms. Radiograph is non-diagnostic except for showing its presence in symptomatic cases. 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.

MRI findings of painful accessory navicular bone usually include persistent edema pattern in the accessory navicular bone and within the synchondrosis.

Development of multimodality SPECT/CT has allowed the high sensitivity of SPECT to be combined with the specificity of CT allows assessment of both morphology and physiology in a single study. CT images provide a precise anatomical localization of the site (s) of radiotracer uptakes. As in this case has shown focal increased tracer uptakes in the symptomatic left foot accessory navicular bone reflecting ongoing bony metabolism and remodeling. CT images also provide additional structural detail about anatomical structures within the imaged volume in which there is no active uptake of radiotracer as seen in right foot accessory navicular bone region and therefore, likely to be quiescent.