A case-control study evaluating CT signs of xiphoid process associated with xiphodynia

Objectives：To investigate whether CT signs of the xiphoid process, such as xiphisternal angle and evidence of soft tissue compression, are useful for diagnosing xiphodynia.

Design：A case-control study within a cohort.

Setting/Participants：Participants included 1560 individuals who visited a small urban hospital in Japan for chest or abdominal pain between January 2021 and September 2023. Those who underwent CT examinations including the xiphoid process were selected. Nine individuals diagnosed with xiphodynia were assigned to the study group, while 321 individuals diagnosed with other causes of pain were assigned to the control group.

Interventions：The xiphisternal angle, evidence of soft tissue compression anterior to the xiphoid process, anatomical features at the tip of the xiphoid process, and anatomical morphology of the xiphoid process were compared between the two groups.

Results：There was no significant difference in the xiphisternal angle between the two groups. No significant differences were observed in evidence of soft tissue compression anterior to the xiphoid process or anatomical features at the tip of the xiphoid process. New anatomical signs reveal that in approximately 70% of cases, the xiphoid process curves forward and then backward.Xi

Conclusions：The xiphoid process sternal angle is not useful for diagnosing xiphodynia. The curvature of the xiphoid process is frequently observed regardless of the presence of xiphodynia.

Methods
Population 

This study targeted patients who visited the internal medicine outpatient department of Kameyama Municipal Medical Center between January 2021 and September 2023 with complaints of chest pain or abdominal pain. Case group were defined as patients diagnosed with xiphodynia who underwent CT scans including the xiphoid process. Diagnosis of xiphodynia was defined as meeting all of the following criteria: (1) presence of chest or upper abdominal pain, (2) reproducible tenderness upon palpation of the xiphoid process, (3) absence of other conditions more likely than xiphodynia as the cause of pain, and (4) improvement of pain with local injection of anesthetic agents onto the xiphoid process or xiphoid process excision surgery. Control groups were defined as patients who underwent CT scans including the xiphoid process and were diagnosed with other conditions than xiphodynia as the cause of pain. Patients with unknown causes of pain were excluded from the control group.

Data collection

Patient data were accessed for research purposes from 01/10/2023 to 31/03/2024.　Medical records were reviewed to extract demographic information including age, gender, site of pain, and underlying cause of pain.

Measurement of CT signs

CT examinations were utilized to measure signs of interest. Sagittal images were created, incorporating the xiphoid process from the thinnest axial section.

The xiphisternal angle was measured using a method that we defined due to its absence in previous literature. We identified two patterns for measurement: one between the xiphoid process and the sternal body angle, and the other between the xiphoid process and the base of the xiphoid process. Additionally, variations in the xiphoid process, such as bending midway or inversion, were considered, leading to the definition and measurement of four angles: the xiphoid-sternal body angle (XSBA), xiphoid to xiphoid base angle (XXBA), xiphoid tip to sternal body angle (XTSBA), and tip to base angle of the xiphoid process (TBAXP), as illustrated in Fig2.

The definition of the xiphisternal angle.

A: A line connecting the midpoint of the cranial end and the midpoint of the caudal end of the sternal body.

B: A tangent line to the midline of the base of the xiphoid process (excluding the xiphisternal joint).

C: A tangent line to the midline at the maximum ventral curvature of the xiphoid process.

D: A tangent line at the tip of the xiphoid process.

XSBA: The angle between line A and line C, with line A as the baseline.

XXBA: The angle between line B and line C, with line B as the baseline.

XTSBA: The angle between line A and line D, with line A as the baseline.

TBAXP: The angle between line B and line D, with line B as the baseline.

Regarding compression signs caused by the xiphoid process, we assumed and measured the anterior shift of the rectus abdominis (ASRA), anterior shift of the skin surface (ASSS), and thinness of the subcutaneous tissue (TST) as useful indicators. As for anatomical signs at the tip of the xiphoid process, we measured the penetration of the xiphoid tip into the rectus abdominis (PXTRA), calcification of the xiphoid tip (CXT), and hypertrophy of the rectus abdominis (HRA) in contact with the tip of the xiphoid process. The definitions for each sign are as follows:　(1) ASRA: At the most ventral projection of the xiphoid process, the rectus abdominis shifts anteriorly. (2) ASSS: At the most ventral projection of the xiphoid process, the skin surface line shifts anteriorly. (3) TST: Subcutaneous tissue compressed by the xiphoid process is thinner than surrounding tissue. (4) PXTRA: The tip of the xiphoid process contacts the rectus abdominis, and the tip and rectus abdominis are not parallel. (5) CXT: In CT abdominal conditions, there is calcification at the tip of the xiphoid process. (6) HRA: At the point of contact with the xiphoid process, the rectus abdominis is thicker than the surrounding rectus abdominis. For cases with multiple tips of the xiphoid process, measurements for each sign were taken at the tip with a positive PXTRA. In cases where this criterion was not applicable, measurements were taken at the longest tip.

As additional items for CT signs, we recorded the imaging range of the CT, the slice thickness of the original CT images, and anatomical features of the xiphoid process (shape, number of tips, xiphoid foramen, fractures). Regarding the shape of the xiphoid process, forward curvature was denoted as "F", backward curvature as "B", and the curvature sequence from the base of the xiphoid process was represented (e.g., if the sequence is F→B→F, it is labeled as "FBF type"), defining it based on the number and direction of curvatures. All observations were assessed by the same evaluator.