HR Beaks and peaks in adult skeleton, Part I: Bony excrescences in skull base and upper extremity, p. 28-37 J VOLUME 5 | ISSUE 1 PICTORIAL ESSAY MSK Imaging Beaks and peaks in adult skeleton, Part I: Bony excrescences in skull base and upper extremity Zehra Akkaya, Ayşegül Gürsoy Çoruh, Gülden Şahin Ankara University, School of Medicine, Department of Radiology, Ankara, Turkey Submission: 12/12/2019 | Acceptance: 8/3/2020 Abstract Bony protrusions which may be part of normal or vari- lesions are detected incidentally, to being associated ant anatomy or de novo pathologic conditions can have with severe pain and limited range of motion due to im- particular imaging and clinical findings. They can arise pingement and mass effect on the surrounding tissues. as a result of overuse injuries and trauma. Additionally, The purpose of this pictorial review is to overview some some bony spurs may have an evolutionary base. Some common and some infrequent but important bony ex- of them can result from a previous injury whereas some crescences, by emphasising on their clinical importance others are the reason for the injury of neighbouring and differential diagnoses based on their imaging find- structures themselves. Presenting symptoms may also ings. This first part of the review covers the skull base vary accordingly, from being asymptomatic, where the and upper extremity with emphasis on the latter. Key words Imaging/diagnosis; Bone spur; Exostoses; Skull; Radiography; Upper extremity Corresponding Zehra Akkaya, Author, Ankara University, School of Medicine, Department of Radiology, Keklikpinari Guarantor mahallesi Dikmen caddesi 913. Sokak Turtaş Sitesi A-8 Blok No:14 Çankaya-Ankara, Turkey, Email: [email protected] 28 Beaks and peaks in adult skeleton, Part I: Bony excrescences in skull base and upper extremity, p. 28-37 HR VOLUME 5 | ISSUE 1 J Introduction Adult human skeleton has numerous bony protrusions, ridges, crests and tubercles which are common sites of apophyses and entheses. These sites might be involved in various degenerative, inflammatory or overuse trau- ma related disorders, where they undergo hypertrophic changes. Moreover, acquired or congenital exophytic bony le- sions, variations of normal anatomic bony excrescenc- Fig. 1. Sagittal oblique reformatted (a) and coronal volume es in particular locations may be of clinical relevance, rendered (b) CT images of a 77-year-old female patient with which can shed light to the diagnosis in the right clinical dysphagia reveal bilateral abnormally long styloid processes context. and ossification of stylohyoid ligaments (arrows), compatible Radiologists are often quite familiar with these struc- with "Eagle" syndrome. Note that the calcified ligament ends tures. However in some cases, distinguishing between a at the upper border of hyoid bone (asterisk in a) on the left normal bony excrescence and a pathologic condition can side. be difficult for inexperienced eyes. A classic example is the “pseudotumour deltoideus”, which refers to the spec- trum of anatomic variants at the level of deltoid tubercle of humerus [1]. Furthermore in some cases, these bony excrescences may appear subtle, thus may be missed on standard radiographs unless special projections or cross sectional imaging modalities are used [2-4]. The purpose of this review is to make radiologists fa- miliar with imaging findings related to various benign bony excrescences in the adult skull base and upper ex- Fig. 2. Axial (a) and sagittal reformatted (b) cranial CT im- tremity, with special attention to those associated with ages of a 74-year-old male patient with a painless hard lump clinical relevance or those posing a challenge in the diag- at the back of his head are shown. The images depict an os- nostic workup with emphasis on appendicular skeleton. teoma (open arrow) arising from the posterior table of the oc- cipitoparietal bones at the site of external occipital protuber- 1. Skull base ance. Note the associated posterior table thickening around 1.1. Eagle syndrome the lesion (arrows). At the four-year follow up, the lesions Eagle syndrome is associated with an abnormally long remained stable and the patient pain free. (more than 3 cm) styloid process or ossification of sty- lohyoid ligament (Fig. 1). It is more common in women and uncommon before 30 years of age [5]. Depending on tion in the periosteum. They predominate in the cranio- the anatomical structure the elongated styloid process facial bones, especially in the ethmoid and frontal sinus- impinges on, a wide range of clinical findings have been es. In addition, they can arise from the inner and outer reported, such as glossopharyngeal neuralgia, kinking tables of the cranial vault, mandible and maxilla. They and compression of internal carotid arteries, Horner are commonly encountered in the fourth or fifth decades syndrome and syncope [5-8]. Computed tomography of life and are asymptomatic, unless they encroach on (CT), particularly 3D volume rendered and reformatted nearby structures, causing mass effect. On imaging they images, is the most robust diagnostic modality, where appear as smoothly contoured, homogeneous, densely additional surgical planning and precise measurements sclerotic nodular bone lesions without soft tissue com- can be performed with high accuracy [8]. ponent, on the surface of a parent bone or within crani- ofacial sinuses (Fig. 2). On follow up they usually remain 1.2. Calvarial osteomas unchanged. Differential diagnosis includes parosteal Osteomas represent abnormally dense new bone forma- osteosarcoma, ossifying parosteal lipoma and myositis 29 HR Beaks and peaks in adult skeleton, Part I: Bony excrescences in skull base and upper extremity, p. 28-37 J VOLUME 5 | ISSUE 1 Fig. 4. 20-year-old professional male volleyball player who complains of posterior right shoulder pain during spiking. Ax- ial (a) and oblique sagittal reformated (b) CT images and cor- responding axial fat suppressed proton density (c) and oblique sagittal T1-weighted (d) images of his right shoulder reveal a bony spur (arrows) and associated capsular oedema (open ar- row in c) on the posterior rim of the glenoid, compatible with Fig. 3. Lateral cervical radiograph of a 24-year-old male pa- a Bennett lesion. tient who was referred for imaging after a fall. Note the en- larged external occipital protuberance (arrow) in this young gested that increased forward head protraction could be patient. Unlike an osteoma (Fig. 2), an enthesophyte is pointy related to higher mechanical loading on posterior crani- in appearance and is not associated with outer table thick- ocervical soft tissues [10, 12]. ening. 2. Upper Extremity 2.1. Scapula ossificans [9]. 2.1.1. Bennett Lesion Bennett lesion, originally described in baseball players 1.3. Enlarged external occipital protuberance as an extraarticular exostosis at the posteroinferior bor- External occipital protuberance or the “inion” can be a der of the glenoid, in the proximity of posterior inferior site of enthesophyte formation [10]. Unlike most enthe- glenohumeral ligament, is now accepted to be associated sophytes or ligament ossifications, which are commonly with several overhead activities [4, 13, 14]. Radiographi- considered to be associated with ageing, enlarged exter- cally, it can be diagnosed on axillary, Bennett, or Stryker nal occipital protuberance (longer than 1 cm on lateral notch views [4]. radiographs) (Fig. 3) has been reported to occur more On plain films and CT it appears as a crescent shaped commonly in patients between the ages of 18-30, par- mineralisation at the posterior inferior rim of the gle- ticularly in males [10, 11]. Additionally, forward head noid process where posterior capsule and posterior bun- protraction was found to be associated with enlarged dle of inferior glenohumeral ligament attach [15]. CT is external occipital protuberance, where with increased more sensitive for the detection of the capsular miner- degrees of protraction, the likelihood of having an en- alisation. However, magnetic resonance imaging (MRI) larged external occipital protuberance increases [10]. can detect symptomatic or early Bennett lesion with soft Forward head protraction was lower in patients imaged tissue oedema at the non-mineralised posterior glenoid prior to hand-held technology revolution, thus it is sug- process or periosteal enthesopathic change (Fig. 4) [16]. 30 Beaks and peaks in adult skeleton, Part I: Bony excrescences in skull base and upper extremity, p. 28-37 HR VOLUME 5 | ISSUE 1 J Fig. 5. Anteroposterior cervical (a) and lateral scapular (b) radiographs of a 33-year-old female patient with pain and crepitation upon abduction of the left shoulder reveal an ex- Fig. 6. Axial (a) and coronal oblique reformatted CT images ostotic bony mass (dashed line) originating from the ventral (b) of the left scapula of the same patient as in Fig. 3 demon- surface of the upper scapula. strate the close relationship of ventral scapular osteochon- droma (arrows) with the posterior aspect of the second rib (open arrow) and its origin from the medial ventral surface Although, according to recent literature, Bennett le- of the scapular body. On axial T2-weighted MR image (c) and sion has been only associated with higher incidence of corresponding fat suppressed contrast enhanced T1-weight- posterior glenoid cartilage injuries, a high index of sus- ed image (d), the adventitial bursitis around its tip is seen picion regarding the presence of concomitant abnor- as a fluid-filled sac with thin septal