Secondary Short-Lasting Unilateral Neuralgiform Headache with Conjunctival Injection and Tearing: A New Case and a Literature Review.

Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) is a primary headache syndrome with an unclear pathogenesis. However, there is increasing evidence in the literature for secondary SUNCT being attributable to certain known lesions. We explored the possible neurobiological mechanism underlying SUNCT based on all reported cases of secondary SUNCT for which detailed information is available. Here we report a case of neuromyelitis optica spectrum disorders that had typical symptoms of SUNCT that might have been attributable to involvement of the spinal nucleus of the trigeminal nerve. We also review cases of secondary SUNCT reported in the English-language literature and analyze them for demographic characteristics, clinical features, response to treatment, and imaging findings. The literature review shows that secondary SUNCT can derive from a neoplasm, vascular disease, trauma, infection, inflammation, or congenital malformation. The pons with involvement of the trigeminal root entry zone was the most commonly affected region for inducing secondary SUNCT. In conclusion, the neurobiology of secondary SUNCT includes structures such as the nucleus and the trigeminal nerve with its branches, suggesting that some cases of primary SUNCT have underlying mechanisms that are related to existing focal damage that cannot be visualized.

INTRODUCTION

Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) is a primary headache syndrome mentioned in the third part [covering trigeminal autonomic cephalalgias (TACs)] of the International Classification of Headache Disorders, third edition, beta version (ICHD-IIIβ), and is characterized by moderate-to-severe strictly unilateral head pain. The condition is typically characterized by the occurrence of at least 20 attacks lasting 1–600 seconds that involve both ipsilateral conjunctival injection and lacrimation.1 However, the increasing number of cases of secondary SUNCT attributed to neoplasms, neurovascular compression, infection, inflammation, trauma, and congenital malformations suggests that SUNCT could be a secondary symptom.

Here we report a patient who had SUNCT attributed to demyelination. We also critically review published secondary SUNCT cases for which detailed information from magnetic resonance imaging (MRI) is available up to April 2017, and analyze their etiology and focus location. Through reviewing our own cases and all previously published cases, we aimed to summarize the location of lesions that are more likely to induce secondary SUNCT and identify the possible pathogenesis of secondary SUNCT.

METHODS

This study was conducted in two parts: 1) an assessment of a single case from our clinic and 2) a literature review. We defined secondary SUNCT as a SUNCT-like symptom with an etiology corresponding to the diagnosis of SUNCT and secondary headache in ICHD-IIIβ. The literature review was conducted using the online database PubMed. All papers published in English were searched using the terms SUNCT, secondary SUNCT, and systematic SUNCT (last performed in April 2017). References in the discovered papers were also systemically reviewed to identify additional cases published in other articles or abstracts. The inclusion criteria for the literature review were as follows: 1) diagnosis of SUNCT in accordance with ICHD-IIIβ1 and 2) detailed description of competing etiologies or secondary forms of SUNCT such as a neoplasm, vascular disease, or infection. The information extracted for each case included the following: 1) etiology, 2) age at onset, 3) sex, 4) duration, 5) frequency, 6) trigger, 7) pain side, 8) focus location in MRI/CT, and 9) effective treatment.

Some of the cases identified in the literature review might have been included multiple times due to the presence of repeated reports on them without this being indicated.

RESULTS

Case report

A previously healthy 29-year-old male developed paroxysmal vomiting lasting for 2 months, headache, and right-sided visual loss, and began walking unsteadily for approximately 15 days prior to his admission on October 13, 2016. More details of the medical history are provided in Figs. 1, 2, 3, 4.

Fig. 1

Medical history. AQP4-ab: aquaporin-4 antibody, CSF: cerebrospinal fluid, MBP-ab: myelin basic protein antibody, MRI: magnetic resonance imaging.

Fig. 2

MRI performed on August 9 showed slightly long T1-weighted (A), and T2-weighted (B) values for the splenium of the corpus callosum (arrowheads) with a high diffusion-weighted-imaging signal (C), and equal T1 signal (D), slightly high T2 (E), and T2 Flair values (F) for the right middle cerebellar peduncle (arrowheads).

Fig. 3

Enhanced lesion on October 16 located near the left ventral medulla (arrowhead) in axis (A) and extended from the dorsolateral of lower medulla oblongata to the C1 level (arrowhead) in the sagittal position (B).

Fig. 4

MRI in May showed the enhanced lesion in the optic nerve (arrowheads) of the right eye (A and B), while the left side was normal (C).

His white blood cell count was 11.17×109/L (normal: 3.5– 10×109/L) and the neutrophil count was 0.736% (normal: 0.50–0.70%), which may have been due to the taking of corticosteroids. A lumbar puncture was performed on October 15. The pressure of the cerebrospinal fluid and its white blood cell count and protein level were 125 mmH2O, 12×106/L (normal: 0–10×106/L), and 628.9 mg/dL (normal: 150–400 mg/dL), respectively. The IgG level was 3.89 mg/dL (normal: 0.0–3.4 mg/dL), and no oligoclonal band was detected.

Treatment with 75 mg of oral indomethacin twice daily upon admission to our hospital had little effect. The treatment frequency was reduced slightly to less than once per hour without alleviation of the headache. After excluding tubercular and other infectious diseases, the patient was treated with 1 g of methylprednisolone daily for 3 days and 60 mg of oral prednisolone thereafter. The patient was ultimately diagnosed with SUNCT attributable to demyelination. The paroxysmal hemicranial headaches with autonomic features had ceased 2 days after starting steroid treatment, and his visual acuity had improved to 0.6 in the right eye and 0.8 in the left. The intraocular pressure had decreased to 19.2 mm Hg and 19.7 mm Hg in the right and left eyes, respectively.

His headache had disappeared but his vision was decreased again in February 2017. After performing several examinations we diagnosed neuromyelitis optica spectrum disorders (NMOSD)2 based on a positive test for serum aquaporin-4 antibody and the presence of standard clinical features of optic neuritis, and attributed his SUNCT-like condition to NMOSD.

Literature review

We summarized 69 cases of SUNCT-like conditions associated with certain etiologies in 62 English-language studies reported on from 1991 to 2017 and for which there were detailed descriptions of the clinical features and imaging results of the patients. These cases comprised 17 with neoplasm,3456789101112131415161718 35 with neurovascular disease,19202122232425262728293031323334353637383940414243 2 with trauma,4445 10 with infection,464748495051525354 3 with inflammatory disease,555657 and 2 with congenital malformation (Table 1, 2, and 3).5859

Table 1

Clinical features of 17 patients with short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing attributed to neoplasm

Disease	Patient no.	Age at onset (years)	Sex	Duration (seconds)	Frequency (per day)	Trigger	Pain side	Focus location in MRI/CT	Effective treatment
Pituitary macroadenoma	17	26	M	20–30	1–6	Yes	R	R cavernous sinus and carotid artery	BCT
	216	33	M	10	1–10	Yes	L	L cavernous sinus	DA
	318	35	F	60–120	40	Yes	R	R cavernous carotid artery	LMT
	43	27	F	15–30	N/A	Yes	L	L cavernous sinus	Radiotherapy
Pituitary adenoma	513	46	M	15–120	3–6	Yes	L	L cavernous sinus	CAB
	612	22	F	<60	5–10	Yes	L	No extension	CAB
	7*10	26	M	60	2–8	N/A	L	No extension	Surgery
	814	18	F	30	5–10	No	B	No extension	LMT
Pituitary microadenoma	93	24	F	15–30	10–30	Yes	L	No extension	Surgery
	109	28	M	20–30	100–200	N/A	R	No extension	Surgery
	1111	33	M	60–120	30	N/A	L	No extension	Surgery
Leiomyosarcoma	125	45	M	60–120	10–15	Yes	L	L cavernous sinus	N/A
Pilocytic astrocytoma	134	11	F	30–60	20	No	R	R pons–CPA	Surgery
Epidermoid tumor	1417	33	M	30–60	240	Yes	L	L pons–CPA	Surgery
Cyst	156	23	F	10–60	20–30	Yes	R	R ocular region	Surgery
Pulmonary metastases	168	69	F	60–120	50–70	Yes	R	R ocular region	Radiotherapy
Meningioma	1715	81	F	N/A	60	No	L	L frontotemporal infiltrative growing	GBP

*Nonfunctioning adenoma.

BCT: bromocriptine, CAB: cabergoline, CPA: cerebellopontine angle, CT: computed tomography, DA: dopamine, GBP: gabapentin, LMT: lamotrigine, MRI: magnetic resonance imaging, N/A: not applicable.

Table 2

Clinical features of 35 patients with short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing attributed to vascular disease

Disease	Patient no.	Age at onset (years)	Sex	Duration (seconds)	Frequency (per day)	Trigger	Pain side	Focus location in MRI/CT	Effective treatment
Neurovascular compression	1819	33	M	30	360	No	L	L pons–CPA–arteriovenous malformation	CBZ
	1920	55	M	30	280–360	Yes	R	R pons–CPA–vascular malformation	CBZ, AMT
	2022	43	F	30–45	6–7	Yes	R	R pons–PCC–SCA	MVD
	2125	54	F	60–120	N/A	Yes	L	L pons–PCC–SCA	MVD
	2226	47	M	60	30–40	Yes	R	R pons–PCC–SCA	MVD
	2333	67	M	1–60	<720	Yes	R	R pons–PCC–SCA	DBS
	2434	45	F	Seconds	20–60	Yes	L	L pons–PCC–SCA	MVD
	2536	44	M	30–60	>20	Yes	R	R pons–PCC–SCA	OXA, LMT
	2630	57	M	30–120	120–240	N/A	L	L pons–PCC–SCA VL	MVD
	2731	54	M	5–10	3–10	Yes	L	L pons–PCC–SCA VL	MVD
	2832,40	65	F	60–180	30–200	Yes	R	R pons–PCC–SCA VL	MVD
	2932	65	M	60–120	30–200	Yes	R	R pons–SCA	N/A
	3032,40	43	M	30–120	20–30	No	L	L pons–AICA	LMT, lignocaine
	3132,40	46	F	3–10	90–120	Yes	R	R pons–SCA	LMT, lignocaine
	3232	44	F	30–120	100–300	Yes	N/A	Pons–SCA	N/A
	3332,40	19	M	20–180	8–10	Yes	L	L pons–SCA	LMT
	3435	60	M	20–30	20–50	Yes	R	R pons–PCC–SCA VL	OXA, LMT
	3535	55	M	10–90	25–30	Yes	R	R pons–SCA VL	LMT
	3635	64	M	10–30	5–30	Yes	R	B pons–SCA VL	CBZ
	3736	46	M	30–60	1–6	Yes	R	R pons–SCA VL	CBZ, IM
	3836	50	F	2–180	>100	Yes	R	R pons–SCA VL	MVD
	3924	48	M	20–30	15–20	Yes	L	L pons–AICA	None
	4027	68	M	60–120	3–7	N/A	L	L pons–BA VL	GBP
	4128	55	M	30	20–30	No	L	L pons–vertebrobasilar	None
	4239	52	M	360	N/A	Yes	R	R pons–PCC–VA	MVD
	4339	65	M	Seconds	N/A	N/A	R	R pons–PCC–SCA, AICA	MVD
	4441	46	F	60–120	N/A	Yes	R	R pons–PCC–SCA	MVD
	4541	69	F	120–180	N/A	Yes	R	R pons–PCC–SCA	CBZ
	4642	43	F	30–45	6–7	Yes	R	R pons–SCA	MVD
	4743	40	F	<300	2–30	Yes	R	R pons–SCA	LMT, GBP, amitriptyline
Cerebellar infarction	4823	63	M	20–180	8	Yes	L	L pons–ischemic–penumbra of cerebellar	N/A
	4929	54	M	20	10	No	R	R dorsolateral medulla	None
	5037	64	M	3–10	1–4	No	L	L dorsolateral medulla	N/A
	5138	58	M	20	12–15	Yes	R	R dorsolateral medulla	CBZ, GBP
Cavernous angioma	5221	60	M	60	15–23	N/A	L	L pons	CBZ

AICA: anterior inferior cerebellar artery, AMT: amitriptyline, BA: basilar artery, CBZ: carbamazepine, CPA: cerebellopontine angle, CT: computed tomography, DBS: deep brain stimulation, GBP: gabapentin, IM: indomethacin, LMT: lamotrigine, MRI: magnetic resonance imaging, MVD: microvascular decompression, N/A: not applicable, OXA: oxcarbazepine, PCC: pontocerebellar cistern, SCA: superior cerebellar artery, VA: vertebral artery, VL: vascular loop.

Table 3

Clinical features of 17 patients with short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing attributed to other etiologies

Disease	Patient no.	Age at onset (years)	Sex	Duration (seconds)	Frequency (per day)	Trigger	Pain side	Focus location in MRI/CT	Effective treatment
Head injury	5344	20	M	20–60	160	Yes	R	None	CBZ
Whiplash injury	5445	62	F	120–240	40–50	Yes	R	None	GON blocks
Sinusitis	5547	53	M	5–10	144	Yes	L>R	B maxillary sinuses	FESS
Ethmoid sinusitis	5649	71	M	3–5	>100	N/A	R	R ocular region	FESS
Sphenoiditis	5752	62	F	60–240	>20	N/A	R	R sphenoid sinus	AMX–clavulanate
Orbital venous vasculitis	5846	49	M	300–600	1–180	Yes	R	None*	Steroids, AZA
Viral meningitis	5950	49	M	10	100–200	N/A	R	None†	Sumatriptan
VZV meningoencephalitis	6048	46	F	30–60	240	No	R	None‡	VPA
	6153	72	M	10–60	20–40	Yes	R	None‡	GBP
VZV	6254	58	M	20	96–120	Yes	R	None	Pregabalin, LMT
	6354	60	M	10–60	120	N/A	L	None	Pregabalin
	6451	57	F	5–30	50–100	No	L	Cervical spinal cord (C2/C3, C5/C6)	GBP
NMO	6555	41	F	10–15	20	N/A	L>R	Medulla to cervical spinal cord (C6); ocular region	MP, IVIg
MS	6656	18	M	5–30	20	N/A	R	R medulla; pons; cervical spinal cord.	N/A
	6757	59	F	Seconds	720	N/A	L	L pons	Steroids, CMZ, IM
Osteogenesis imperfecta	6858	42	M	120–180	1–5	Yes	L	Basilar impression; L pons	CBZ
Craniosynostosis brachycephaly	6959	14	F	60	50	Yes	R	Foreshortened posterior fossa; more notable in the R pons–CPA	CBZ, PDN, lithium carbonate

*Narrowing of superior ophthalmic vein, †Thermogram showed that the skin temperature was higher around the orbital region than around the left side, suggesting decreased right sympathetic nerve function, ‡CT scans were normal when headache started. The author considered them to be a peripheral mechanism.

AMX: amoxicillin, AZA: azathioprine, CBZ: carbamazepine, CMZ: carbimazole, CPA: cerebellopontine angle, CT: computed tomography, FESS: functional endoscopic sinus surgery, GBP: gabapentin, GON: greater occipital nerve, IM: indomethacin, IVIg: intravenous immunoglobulin, MP: methylprednisolone, MRI: magnetic resonance, MS: multiple sclerosis, N/A: not applicable, NMO: neuromyelitis optica, PDN: prednisone, VPA: valproic acid, VZV: varicella-zoster virus.

SUNCT secondary to neoplasm

Eleven of the cases were secondary to pituitary adenoma,37910111213141618 of which four were macroadenoma371618 and three were pituitary microadenoma.3911 The other six cases comprised leiomyosarcoma,5 pilocytic astrocytoma,4 epidermoid tumor,17 cyst,6 pulmonary metastases,8 and meningioma.15 MRI findings showed that five cases were located in the cavernous sinus, two in the pons, two in the ocular region, two in the carotid artery, and one in the frontotemporal area. Another six cases comprising three pituitary microadenomas and three pituitary adenomas showed no extension in MRI.

SUNCT secondary to neurovascular disease

Thirty cases were caused by neurovascular compression,192022 2425262728303132333435363940414243 four cases were due to cerebral infarction,23293738 and one case was due to cavernous angioma.21 MRI findings showed that 32 cases were at the pons level, including a case of left cerebellar infarction, while its ischemic penumbra was considered to involve the ascending spinothalamic tract and descending trigeminal fibers at or below their site of entry (and subsequent caudal passage) into the lateral pontine tegmentum. Three cases were located in the unilateral dorsolateral medulla with the possible involvement of the spinal nucleus of the trigeminal nerve.

SUNCT secondary to other etiologies

The cases with other etiologies showed scattered focus locations. The trauma areas included head and whiplash injuries. The infection areas covered the chronic sinusitis, ethmoid sinusitis, sphenoiditis, and orbital venous vasculitis, and included two cases of viral meningitis/meningoencephalitis and three of varicella-zoster virus infection. Inflammation included one case of neuromyelitis optica and two cases of multiple sclerosis, both of which were due to congenital malformation with skull abnormalities.

Focus location

According to the etiology classification (Table 4), the most common location of the neoplasm was the cavernous sinus (5/18), followed by the pons, ocular region, and carotid artery (each 2/18), and then the frontotemporal area (1/18). Moreover, another six cases of pituitary adenoma showed no extension out of the sellar space, one of which was a nonfunctioning adenoma associated with headaches that ceased after surgery or administering cabergoline. In cases with vascular disease, the pons (32/35) and medulla (3/35) were common locations at which SUNCT was induced. Six of the ten cases of infectious disease and both traumatic cases showed no abnormalities in imaging, while the focus in the other four cases of infection was in the cervical spinal cord, ocular region, maxillary sinus, and sphenoid sinus. Since the focal lesions were scattered throughout demyelinated areas, we only focused on the most likely locations such as the pons, medulla, and cervical spinal cord (two cases), and the ocular region (one case). The focal lesions were difficult to locate in the two cases of congenital malformation due to skull abnormalities, but the most likely location was the pons in both cases.

Table 4

Distribution of lesion locations according to the etiology classification

Variable	n (%)
Neoplasm (n=18)
No extension	6 (33.33)
Cavernous sinus	5 (27.78)
Pons	2 (11.11)
Ocular region	2 (11.11)
Carotid artery	2 (11.11)
Frontotemporal area	1 (5.56)
Vascular disease (n=35)
Pons	32 (91.43)
Medulla	3 (8.57)
Trauma (n=2)
None	2 (100)
Infection (n=10)
None	6 (60)
Maxillary sinus	1 (10)
Ocular region	1 (10)
Sphenoid sinus	1 (10)
Cervical spinal cord	1 (10)
Demyelination* (n=3)
Pons	2 (66.67)
Medulla	2 (66.67)
Cervical spinal cord	2 (66.67)
Ocular region	1 (33.33)
Congenital malformation (n=2)
Pons	2 (100)

*Demyelination had multiple focuses, each of which could be the lesion responsible for inducing short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing.

According to the classification of focus location (Table 5), the pons was the most common location where SUNCT-like syndrome was induced, and 32 cases were vascular diseases while 6 involved neoplasms, demyelination, and congenital malformations. The second most common locations were the medulla and cavernous sinus, each comprising five cases. The medulla accounted for three cases of vascular disease and two cases of demyelination, and the cavernous sinus was only involved in cases of neoplasm. The third and fourth most common locations were the ocular region (two cases with neoplasm and two with infection or demyelination) and cervical spinal cord (two cases with demyelination and one with infection), respectively. The carotid artery (two cases of neoplasm), frontotemporal area (one case of neoplasm), maxillary sinus (one case of infection), and sphenoid sinus (one case of infection) were less common locations. In addition, no lesions were detected in imaging investigations in six cases of infection and two of trauma, but two cases of infection showed narrowing of the superior ophthalmic vein and a higher temperature around the ipsilateral orbital region. Finally, the tumor did not extend to adjacent tissues in six cases of pituitary adenoma.

Table 5

Distribution of etiology according to the classification of lesion location

Location	n (%)
Pons (n=38)
Vascular disease	32 (84.22)
Neoplasm	2 (5.26)
Demyelination	2 (5.26)
Congenital malformation	2 (5.26)
Medulla (n=5)
Vascular disease	3 (60)
Demyelination	2 (40)
Cavernous sinus (n=5)
Neoplasm	5 (100)
Ocular region (n=4)
Neoplasm	2 (50)
Infection	1 (25)
Demyelination	1 (25)
Cervical spinal cord (n=3)
Demyelination	2 (66.67)
Infection	1 (33.33)
Carotid artery (n=2)
Neoplasm	2 (100)
Frontotemporal area (n=1)
Neoplasm	1 (100)
Maxillary sinus (n=1)
Infection	1 (100)
Sphenoid sinus (n=1)
Infection	1 (100)
None (n=8)
Infection	6 (75)
Trauma	2 (25)
No extension (n=6)
Neoplasm	6 (100)

DISCUSSION

SUNCT is a primary headache classified as a TAC.1 However, increasing numbers of SUNCT cases with known etiology have been reported. The case included in the present study was diagnosed as secondary SUNCT since it fulfilled the ICHD-IIIβ diagnostic criteria for SUNCT and was attributable to NMOSD,2 which is a rare cause that has seldom been reported previously. The case with a left-sided headache had lesions on the contralateral cerebellopontine angle (CPA) and ipsilateral medulla. However, the lesion on the CPA appeared at least 2 months before the onset of the headache, and so we considered the lesion on the dorsolateral medullar to be the one responsible. Moreover, we summarized the focus locations of 69 cases that met the ICHD-IIIβ diagnosis criteria for SUNCT and were attributed to neoplasms, vascular disease, trauma, infection, inflammation, and congenital malformations, indicating that secondary SUNCT indeed exists. The exact pathogenesis of secondary SUNCT has not yet been well established, but our findings have revealed that there are certain main areas where SUNCT is induced.

The probable SUNCT-related trigeminal nerve conduction pathway60 is illustrated as follows (Fig. 5): First, the afferent pathways (sensory fibers) comprising the primary neurons of the trigeminal nerve are located in the trigeminal ganglion, with peripheral processes distributed among the head and facial, skin, oral, and nasal mucosa receptors. After entering the pons, nociceptive afferents of the central process terminate in subnuclei of the trigeminal brainstem nuclear complex. Some of the fibers of the secondary neurons in the nuclear complex and the gray matter of upper cervical spinal cord segments (C1 to C2) form the trigeminohypothalamic tract61 and then project to or go through the hypothalamus. The other fibers from the sensory and spinal nucleus of the trigeminal nerve cross upward, and the composite trigeminal lemniscus terminates in the ventral posteromedial nucleus of the thalamus, passing the posterior limb of the internal capsule and ending at the postcentral gyrus. Second, the efferent pathways (motor fibers) in the hypothalamus regulate lachrymal gland secretion. Parasympathetic fibers of the facial nerve are sent out by the superior salivatory nucleus and terminate in the pterygopalatine ganglion via the greater petrosal nerve. Postganglionic fibers of the pterygopalatine ganglion are distributed to the mucous membrane in the lachrymal gland, palate, and nosepiece, controlling the exudation of the mucous membrane and gland body.

Fig. 5

Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing-related pathways and structures. Shadow A represents the dorsolateral medulla and upper cervical spinal cord where the spinal nucleus of the trigeminal nerve was located, which was often affected by cerebral infarction and demyelination. Vascular compression was likely to occur in the area of Shadow B. The neoplasm and infection had a widespread focus, and were mostly located at the preganglionic fibers of the trigeminal nerve (Shadow C).

Based on the conduction pathway and images in the literature, we assumed that three areas were mainly responsible for the induction of secondary SUNCT (Fig. 5): 1) the dorsolateral medulla and upper cervical spinal cord where the spinal nucleus of the trigeminal nerve is located (Shadow A in the Fig. 5), 2) the pons (Shadow B) in which vascular compression was likely to occur, and 3) the preganglionic fibers of the trigeminal nerve (Shadow C) that was the focus of neoplasm and widespread infection. Cases with cerebral infarction,23293738 infection,51 and demyelination5556 explicitly manifested in the Shadow-A area because they mainly exhibited lesions in the pons, dorsolateral medulla, and cervical spinal cord (C1 to C2) where the trigeminal divisions, trigeminal nucleus, spinothalamic tract, and trigeminohypothalamic tract are present and thus induce SUNCT. Neurovascular compression1920222425262728303132333435363940414243 was the most common reason in cases in the Shadow-B area, which could be clearly visualized using MRI and could accurately indicate vascular malformation in the CPA cistern that involves the trigeminal root entry zone and mostly irritates fibers of the first division (V1) of the trigeminal nerve and the greater petrosal nerve; thus, patients would present with accompanying conjunctival injection and tearing. However, there were more than 35 cases of neurovascular compression in our review. Williams and Broadley,40 Sebastian et al.60 and Favoni et al.36 reported other cases of SUNCT secondary to neurovascular compression that were excluded from our review due to a lack of detailed information.

In addition, there were focuses in the lateral cavernous sinus, frontotemporal region, maxillary sinus, sphenoid sinus, ocular region, and carotid sinus, and six cases of infection showed no abnormities on MRI/CT, while two of the cases exhibited narrowing of the superior ophthalmic vein46 and a higher temperature around the ipsilateral orbital region.50 These cases also have a high probability of developing invasion into the divisions of the trigeminal nerve because the focus of the neoplasm and infection can sometimes invade the intracranial and extracranial structures associated with pain sensitivity. These include the endocranium and divisions of the trigeminal nerve (frontal, lachrymal, and nasociliary nerves of the ophthalmic, maxillary, and mandibular nerves) that cannot be seen clearly in images, which was inevitably the actual causal lesion for secondary SUNCT. However, six cases of pituitary adenoma showed a focus in the sellar region without extending to the adjacent tissue. These cases comprised three of microadenoma, another three for which the tumor size was not stated explicitly, and one that was a nonfunctioning tumor. Although the pathophysiology of pituitary-associated headache is not well understood, and most authors have suspected it to be related to abnormalities in the hypothalamic-pituitary endocrine system, we still primarily attributed the effect to unseen cadaverous sinus invasion, dural stretching, or local pressure effects because the nonsecreting tumor case10 represented negative evidence that SUNCT-like headaches can also occur when hormone levels are normal. In other words, pain in the V1 area may to some extent arise from pressure or stretching of the first division of the trigeminal nerve adjacent to the cavernous sinus, whereas other nerves such as the oculomotor, trochlear, and abducent nerves will be not involved due to the limitations of the pressure.

Regarding the associated symptoms such as conjunctival injection and tearing, we inferred that the lesions indicated by Shadows B and C in Fig. 5 had mostly invaded the first division of the trigeminal nerve with distribution of the parasympathetic nerve fiber in the mucous membrane in the lachrymal gland. However, due to the conduction pathway being unknown, we only determined that the trigeminal autonomic symptoms were related to the salivary nucleus and could not elucidate how lesions in Shadow-A areas could induce conjunctival injection and tearing.

Our search of the references revealed that the secondary causes for SUNCT can also reportedly cause trigeminal neuralgia and other TACs. For example, vascular compression can induce short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms-like headache36 that is associated with conjunctival injection or lacrimation. Chiari malformation type I,62 focal cervical myelitis,63 diffuse large-B-cell lymphoma of the nasopharynx,64 and upper cervical meningioma65 can induce cluster-like headache, whose lesions were similar to those of SUNCT. Although our extensive literature search did not reveal a feasible mechanism to indicate the difference, we speculate that affected anatomical structures are the main reason.

Secondary SUNCT will occur with damage to the nucleus, tracts, and peripheral nerves, and the possibility of secondary symptoms cannot be excluded in primary cases with normal imaging findings because some focal damage cannot be visualized using current imaging methods. We have illustrated that certain aspects of SUNCT might be a secondary symptom. When encountering patients with SUNCT in the clinical situation, the best option for physicians is to perform MRI scans with high-resolution sequences of basal cisterna and pituitary fossa sections.

CONCLUSION

We have presented a special case of secondary SUNCT with demyelination. We also reviewed all reported cases of secondary SUNCT in the English-language literature since this condition was first reported in 1991, and analyzed its etiology, focus location, and pain laterality. Finally, we hypothesized three mechanisms for secondary SUNCT and assumed that some aspects of this condition might be a secondary symptom, although some lesions cannot be visualized.