Serial Changes in Image Findings of Herniation Pits from the First Appearance

Abstract

Backgroud: Herniation pits (HPs) have been considered to be an incidental finding, but recently femoroacetabular impingement (FAI) has been proposed as a possible cause of their formation. The findings on bone scans of HPs are variable in the literature: some showed increased uptake; the majority did not. We hypothesized that serial changes in image findings of HPs would explain the reason for the variable bone scan findings.

Methods: Four patients (5 hips) were followed up for more than 7 years. All patients were women and regularly underwent bone scintigraphy after the diagnosis of breast cancer. Small lesions with increased uptake were first detected on bone scintigraphy at the age of 44 to 64 years. In all cases, the lesions were confirmed by magnetic resonance imaging and follow-up bone scintigrams were taken regularly. Four lesions were also evaluated by computed tomography. Changes in the size of the pits and the intensity of the increased uptake on bone scintigraphy were evaluated.

Results: On the bone scintigrams, the lesions with increased uptake were detected in the femoral neck at 5-20 months after previous negative bone scintigraphy. There had been no events or symptoms associated with the newly detected increased uptake. On follow-up scans, the intensity of the uptake decreased gradually and the areas of increased uptake disappeared completely at 14-50 months after their first appearance. In 3 cases (2 patients), the pit size increased during follow-up.

Conclusions: The areas of increased uptake on bone scintigraphy gradually disappeared in all cases and the increase in pit size was frequent. There was no case in which signs or symptoms suggestive of FAI were noticed.

Keywords: Bone scintigram; Herniation pit; Size change; Uptake change.

Fig. 1. Image findings of a herniation pit in a 43-year-old woman. (A) No increased uptake was identified on the first bone scan taken in August 2006. There was a preexisting herniation pit (black arrow) in the right hip on the plain radiograph. However, there was no increased uptake in the right hip. Approximately 1 year later, the increased uptake area was detected in the left hip on the bone scan and an oval lucent lesion with sclerotic margin was observed in the upper lateral quadrant of the left femoral neck. The size of the left herniation pit increased (white arrow) on the follow-up radiograph and the intensity of the uptake decreased gradually. (B) The increased uptake in the left hip disappeared completely approximately 2 years after first appearance (June 2009). An opening hole (arrow) and a septum (arrowhead) were identified in the herniation pit on computed tomographic images. On magnetic resonance images taken 6 months after the first detection of the increased uptake in the left hip, the interior of the herniation pit demonstrated low signal intensity on T1-weighted image and high signal intensity on T2-weighted image (dagger). The signal intensity of the interior part of the preexisting right herniation pit was low on both T1- and T2-weighted images (asterisk).

Fig. 2. Image findings of a herniation pit in a 59-year-old woman. (A) Increased uptake was detected in the right hip in July 2006 and in the left hip in July 2007. The intensity of increase in uptake decreased gradually in both hips and the areas of uptake disappeared completely in September 2009. (B) A gradual increase in the size of both herniation pits was observed. (C) On computed tomographic images, an opening hole (arrow), septation (arrowhead), and flattening of the outer wall (asterisk) were observed. (D) On magnetic resonance images, the interior part of both herniation pits demonstrated low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Bone marrow edema pattern (arrow) was observed around the newly developed herniation pit in the left hip.