Congenital lesions include thyroglossal duct cyst, dermoid and epidermoid cysts, first and second branchial cleft cysts, Tornwaldt cyst, and ranula.
Thyroglossal duct cyst is the most common congenital neck mass, resulting of failure of involution of thyroglossal duct and persistent secretion of cells duct [6]. It presents as a compressible painless mass in child or young adult. It is an anterior midline suprahyoid or midline/paramidline infrahyoid lesion, which elevates when tongue protrudes if is located around hyoid bone [1, 6]. CT shows low attenuation and thin rim enhancement. Paramidline infrahyoid embedded in strap muscles may show claw sign [6]. T1WI is usually hypointense and T2WI is hyperintense, with rim enhancement if infected. Calcification within this cyst is a specific finding of thyroid carcinoma [2, 6].
Epidermoid and dermoid cysts are congenital inclusion of ectodermal or dermal elements. Epidermoid cyst is a well-delineated mass with fluid contents only, presenting as fluid density or signal and restricted diffusion [6]. Dermoid cyst is well-demarcated mass with fatty, fluid, or mixed intensity or signal [5, 6]. Both present as painless mass in floor of mouth, anterior neck, orbit or nasoglabellar region [3, 6]. Scalloping or remodelling of adjacent bone is common, best evaluated at CT [6].
First branchial cleft cyst is a remnant of first branchial apparatus. It presents as a soft, painless, compressible mass in or adjacent to parotid gland, external auditory canal, or pinna [6]. Must be suspected in a patient with chronic unexplained otorrhea or recurrent parotid space abscess [6]. CT shows well-circumscribed nonenhancing low-density mass. T1WI shows hyposignal and T2WI shows hypersignal cyst. Previous or concurrent infection may present thickened wall and rim enhancement.
Second branchial cleft cyst is a remnant of cervical sinus of His [6]. It is posterolateral to submandibular gland, lateral to carotid space, anterior to sternocleidomastoid muscle [3, 6]. It presents as a painless, compressible lateral neck mass in child or young adult, and may enlarge during upper respiratory tract infection. CT shows nonenhancing low-density cyst. MRI shows nonenhancing cyst whose signal intensity follows cerebrospinal fluid. If infected, may present thickened wall and rim enhancement.
Tornwaldt cyst is a notochordal remnant that presents as midline lesion on posterior nasopharyngeal wall between prevertebral muscles [6]. It is usually asymptomatic and incidental, but may present with postnasal discharge, occipital headache, and halitosis [4, 6]. CT shows a well-circumscribed low-density cyst with wall enhancement. T1WI shows intermediate to high signal, T2WI shows high signal and minimal wall enhancement on post-contrast.
Thoracic duct lymphocele can be congenital or acquired, presenting as a well-circumscribed nonenhancing fluid density/signal cyst in supraclavicular fossa [6].
Ranula is a congenital or acquired retention cyst resulting from trauma or inflammation of sublingual gland or sublingual space minor salivary gland [3-6]. Congenital form is rare. Simple ranula is the most common, confined to sublingual space. Usually presents as 30-year-old with painless swelling of floor of mouth. Diving ranula is a comet-shaped cyst, whose “body” is at submandibular space and “tail” is at sublingual space [6]. Typically presents as submandibular mass, which displaces the submandibular gland. Tail sign represents collapsed sublingual space portion [6]. At MRI, signal intensity follows cerebrospinal fluid. CT shows fluid-density cyst with thin wall enhancement. Current or recent infection may present thickened wall and modify enhancement, T1WI and T2WI signal.
Vascular lesions encompass lymphangioma, venous and venolymphatic malformations.
Lymphangioma is a congenital soft mass in the submandibular space, that may present with airway obstruction [1, 6]. CT shows a low-density mass, where macrocystic form appears well-delineated multiloculated cyst with imperceptible wall and thin septations, and microcystic form appears ill-defined, infiltrative, with minimal rim enhancement. Fluid-fluid levels indicate prior haemorrhage. T1WI shows hyposignal, but high signal indicates prior haemorrhage. T2WI shows hyperintense septated cystic lesions, often transspatial, crossing midline, with mild rim enhancement.
Venous malformation is the most common vascular malformation of head and neck [6]. It is a congenital slow-flow serpiginous vessels [6], presented as lobulated soft tissue mass with fluid attenuation or signal. Phleboliths are pathognomonic [2, 6]. Mass expands with Valsalva maneuver, bending over, crying, haemorrhage, thrombosis, or hormonal changes [6].
Venolymphatic malformation has a nonenhancing lymphatic portion with enhancing venous elements that may have phleboliths. It presents as multilocular cystic spaces with high T2WI signal intensity, with fluid levels, without perceptible wall.
Inflammatory/infectious lesions are mostly represented by reactive lymphadenopathy, more frequent in children [6]. It may present suppurative change or early abscess formation [6]. It is also a common incidental finding in young patients under 30 years old. Consider metastatic disease in adults over 30 years old with prominent node in retropharyngeal space [6]. T1W1 shows low to intermediate signal, T2WI shows intermediate signal intensity. At CT tends to be isodense to muscle, with mild enhancement.
Neoplastic cysts comprise metastatic nodal HPV-related squamous cells carcinoma and thyroid carcinoma [3, 6].
Metastatic nodal squamous cells carcinoma is most commonly ipsilateral to the tumour, along internal jugular nodal chain, and may be heterogeneous, cystic, or solid, rarely calcified [6].
Metastatic nodal thyroid carcinoma is frequently a solid-cystic enlarged node, hypointense at T1WI, with focal calcifications (best seen at CT), most usual in lower neck [6].
Traumatic injuries could be exemplified by ranula, sialocele and lymphocele.
Sialocele presents as a fluctuant, soft, painless sublingual mass. It can be related to penetrating trauma, which causes submandibular duct injury with leakage of saliva into sublingual space [6]. It can also be associated to submandibular duct calculus, which is more frequent [6]. In this case, there is a sublingual space fluid density lesion with rim enhancement, accompanied by dilated submandibular duct. CT best delineates calculus if present.
Lymphocele must be considered in post operative patients with low posterior cervical space supraclavicular cyst pointing toward confluence of internal jugular and subclavian veins [6]. It is a well-circumscribed cyst with fluid density or signal, without visible wall, enhancement, or septa. It may present thickened wall and rim enhancement if complicated by infection.