**5.1 Imaging tests**

Specific features have been described for these bone tumors on radiographs, CT, and MRI scans.

The effort in the evaluation of HNOS imaging should focus on searching for specific radiological features that may point to the diagnosis of HNOS, assessing bone involvement and destruction, evaluating the extent of adjacent soft tissue involvement, and ensuring the resectability of the tumor. And finally, but most importantly, looking for possible distant disease, especially pulmonary metastases. An initial diagnosis of HNOS should be considered when tumors with matrix mineralization are present early in the fourth decade of life.

The radiologic appearance of HNOS depends on the interplay of three processes: bone formation and mineralization, bone destruction, and periosteal bone formation. On plain radiography, an ill-defined radiolucent lesion is usually seen. Early tumors may show a symmetrical widening of the periodontal membrane space about one or more teeth (**Figure 4**). Indeed, Lindquist et al. reported that the widening of periodontal ligament space and inferior dental canal, together with sunburst effect, is almost pathognomonic of osteosarcoma of jaw bone [17]. **Figure 4** shows X-rays of the patient presented in **Figure 1**.

CT and MRI both have their own superiorities in detecting osteosarcoma, and the combination of CT and MRI has proven to improve the diagnostic accuracy for patients suffering from HNOS. Key points that are important when analyzing a CT and MRI scan for a possible HNOS are summarized below.

On CT, key points include assessing:


*Perspective Chapter: Osteosarcomas of the Head and Neck DOI: http://dx.doi.org/10.5772/intechopen.107456*

**Figure 4.** *Radiographic imaging of patient showed in* **Figure 1***, a 35-year-old female with a maxillary osteosarcoma.*

HNOS primarily exhibits osteolysis and/or osteoblastic destruction, as well as having an irregular tumor margin on CT imaging. According to Luo et al. [18], in CT, more than 97% of patients have some degree of bone destruction, presenting lytic (43%), sclerotic (19%), or mixed lytic-sclerotic (35%) lesions, with or without soft tissue involvement (**Figure 5**). The mixed and sclerotic radiological pattern in the head and neck region is highly suggestive of osteosarcoma, with differential diagnosis of metastasis, lymphoma, and chondrosarcoma (**Figure 5**). In purely lytic lesions, the diagnosis can be difficult, as osteosarcomas that mimic hollow areas without new bone formation cannot be differentiated from metastatic disease radiographically. For HNOS, primary features are local or patchy high-density shadows in the medullary cavity with varying degrees of bone destruction and matrix mineralization. In the series of Luo et al., matrix mineralization was present in (86.5%), and high-density osteoid matrix is found in 86% of lesions [15].

It is important to evaluate the cortical, as it can be invaded and eroded by the tumor, which extends into the soft tissues, frequently eliciting a periosteal reaction. The pattern of periosteal reaction can be classified as aggressive or non-aggressive according to Rana et al. [19]. Aggressive reactions include laminated, spiculated (hair-on end, sunburst), disorganized, or Codman triangle reaction patterns, while non-aggressive periosteal reactions include thin, solid, thickly irregular, or septated patterns. Up to 70–87% of the cases have an aggressive periostic reaction [1, 15]. However, sometimes, the tumor grows expanding the bone but without violating the cortex, or it can have a homogeneously radiodense surface, well demarcated from the soft tissues, resembling an osteoma, which may hinder diagnostic suspicion. In the extremities, the Codman triangle signifies subperiosteal bone formation. This feature is less frequent in the head and neck, where the classic "sunburst" appearance of malignant osteoid formation is observed, forming radiopaque striations arising from the tumor.

**Figure 5.**

*Computed tomography of patient showed in* **Figure 1***, a 35-year-old female with a maxillary osteosarcoma.*

The rest of the regional bone structure should be examined as previous bone diseases are found in up to 8% cases [15].

**Figure 5** shows CT imaging of the patient presented in **Figure 1**. On MRI, key points include assessing:


MRI allows a better evaluation of possible soft tissue involvement and relationship with anatomical structures, including the skull base, being crucial to determine the resectability of a tumor in some subsites.

MRI depicts soft tissues and bone marrow infiltration (medulla) better than CT imaging, showing cortical destruction and expansive masses. HNOS tumors may present with low or heterogeneous signal intensities on T1-weighted images and high or heterogeneous signal intensities on T2-weighted images**.** However, features of osteoblastic HNOS on MRI scans are nonspecific and often indistinguishable from those of other types of sarcoma with T2 hyperintense signals and heterogeneous postcontrast enhancement. Nevertheless, the peripheral rim enhancement observed on Gd-enhanced MR images supports the diagnosis of chondroblastic HNOS [16].

Also, non-enhanced and Gd-DTPA-enhanced MR also allows to evaluate intramedullary involvement and to differentiate osteoid matrix and necrotic, hemorrhagic or mucosal content, especially useful in sinonasal subsites. And of course, it also allows to determine the possible neural invasion.

All these features make MRI an important tool that should be considered for the assessment of biopsy taking, preoperative surgical planning, and eventually for adjuvant radiotherapy planning.

Imaging also plays an important role in the evaluation of possible distant metastases, for which the best tool remains PET CT, followed perhaps by a combination of CT + bone scintigraphy. It is important to note that in HNOS distant disease is less frequent than that observed for OS of long bones, occurring in about 5% of patients at diagnosis and affecting mainly the lung [11].

## **5.2 Histology, subtypes, and histological grade**

The varied radiographic appearance of this lesion highlights the importance of histopathologic analysis in the diagnosis of osteosarcomas.
