Sternal Foramina in Patient with Hepatocellular Carcinoma: A Diagnostic Dilemma on Bone Scan.

Presenting known treated case of hepatocellular carcinoma, complaining of non specific backache. 99mTc methylene diphosphonate bone scan showed photopenic area in sternal body, which could be easily thought of osteolytic metastasis from hepatocellular carcinoma; however CT scan revealed it to be sternal foramina- a normal variant of sternum. The possibility of a sternal foramen should be mentioned to the clinician because infiltration, biopsy or acupuncture of this area may lead to fatal cardiac complications. Knowledge of the existence of such anatomic variants is important to avoid misdiagnosis as an osteolytic process.

Introduction

A 37-year-old male, known case of hepatocellular carcinoma presented with mild upper backache was referred to the Department of Nuclear Medicine for bone scan. Bone scintigraphy using Tc-99m methylene diphosphonate (MDP) was performed including single-photon emission computed tomography (SPECT-CT). A small rounded photopenic area was seen in the sternal body. The possibility of an osteolytic lesion or an anatomic variation was considered, and noncontrast CT scan of the involved region was performed. CT confirmed the presence of a large bony defect at the level of the sternal body. Knowledge of the existence of such anatomic variants is important to avoid misdiagnosis as an osteolytic process. The possibility of a sternal foramen should be mentioned to the clinician because infiltration, biopsy, or acupuncture of this area may lead to fatal cardiac complications.

Case Report

A 37-year-old male, known case of hepatocellular carcinoma, post liver resection on follow-up visits complained of upper backache and pain in small joints of hand and feet. He was referred to the Department of Nuclear Medicine for Tc-99m MDP bone scan. Physical examination was unremarkable, and no focal tender area could be elicited. Whole-body bone scintigraphy was performed (Infinia Hawkeye with SPECT-CT). Scan showed rounded area of photopenia in the sternal body [Figures 1 and 2]. CT scan was done which showed defect in the sternum in lower one-third [Figures 3 and 4]. Volume rendered images clearly show sternal foramina [Figure 5]. The differential diagnosis of such a lesion consists of an osteolytic lesion, superposition of a necklace, or a congenital variation. CT scan of the sternum was performed, showing a midline circular defect of the sternal body-sternal foramen. Thus while reporting oncology bone scans, it should be noted that photopenic defects might attribute to congenital variations also, not just osteolytic lesions.

Figure 1

Tc-99m whole body bone scan showed photopenic area in sternum

Figure 2

Oblique spot view image also showed photopenic lesion

Figure 3

Computed tomography scan sagittal view also suggested sternal defect with no lytic/sclerotic component

Figure 4

Volume rendered image from computed tomography scan beautifully demonstrates the defect to be normal variant- sternal foramina

Figure 5

Axial view in computed tomography scan shows sternal defect with no lytic component

Discussion

The embryologic development of the sternum starts from a pair of a long linear cluster of mesenchymal cells on each side of the midline. These structures convert into precartilage and fuse at the midline in a cephalocaudal direction. The cartilage matures as sternum after undergoing multiple transverse divisions into a series of cartilaginous segments, called sternebrae. The ossification nuclei form in the centers of the separate cartilages, and it is not uncommon for these to be paired in all or some of the sternebrae. The failure of fusion will result in cleft sternum or sternal foramen.[1] The location of it is usually in the lower portion of the sternal body[2] and are solitary in most of the cases. Variants such as multiple mesosternal foramina and a manubrial foramen also have been described.[3] In fact, size and appearance of the cleft or foramen may show considerable variation. Sternal foramen is asymptomatic, and it is unlikely to cause pain, although few data in the literature address this possibility. Tc-99m bone scan was very important to prevent useless biopsy in the case. The clinical importance is defect being potential hazard when a puncture is performed in this region. Unfortunately, some cases of fatal cardiac tamponade have been reported after needle insertion at the level of the sternum.[4] The differential diagnosis of this type of abnormality includes osteolytic lesion, superposition by metallic pendant or other material, and sternal foramen. In summary, a sternal foramen as demonstrated on scintigraphy may erroneously suggest the presence of an osteolytic lesion.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.